منصة إيفاد العلمية

د/ أحمد بدر محمد عثمان

إرسال رسالة

التخصص: Animal Physiology

الجامعة: Sohag University

النقاط:

معامل الإنتاج البحثي

الخبرات العلمية

B.Sc. of Science (Zoology), Faculty of Science, Sohag University, Sohag, Egypt.
M.Sc. of Zoology (Animal Physiology), Sohag University, Sohag, Egypt.
Ph.D. of Animal Physiology, University of Eastern Finland, Joensuu, Finland.

الأبحاث المنشورة

Effects of seasonal acclimatization on temperature dependence of cardiac excitability in the roach, R

المجلة: Journal of Experimental Biology

سنة النشر: 2016

تاريخ النشر: 2016-05-15

Temperature sensitivity of electrical excitability is a potential limiting factor for performance level and thermal tolerance of excitable tissues in ectothermic animals. To test whether the rate and rhythm of the heart acclimatize to seasonal temperature changes, thermal sensitivity of cardiac excitation in a eurythermal teleost, the roach (Rutilus rutilus), was examined. Excitability of the heart was determined from in vivo electrocardiograms and in vitro microelectrode recordings of action potentials (APs) from winter and summer roach acclimatized to 4 and 18°C, respectively. Under heat ramps (3°C h−1), starting from the acclimatization temperatures of the fish, heart rate increased to maximum values of 78±5 beats min−1 (at 19.8±0.5°C) and 150±7 beats min−1 (at 28.1±0.5°C) for winter and summer roach, respectively, and then declined in both groups. Below 20°C, heart rate was significantly higher in winter than in summer roach (P<0.05), indicating positive thermal compensation. Cardiac arrhythmias appeared with rising temperature as missing QRS complexes, increase in variability of heart rate, episodes of atrial tachycardia, ventricular bradycardia and complete cessation of the heartbeat (asystole) in both winter and summer roach. Unlike winter roach, atrial APs of summer roach had a distinct early repolarization phase, which appeared as shorter durations of atrial AP at 10% and 20% repolarization levels in comparison to winter roach (P<0.05). In contrast, seasonal acclimatization had only subtle effects on ventricular AP characteristics. Plasticity of cardiac excitation appears to be necessary for seasonal improvements in performance level and thermal resilience of the roach heart.

Spatial uniformity of action potentials indicates base-to-apex depolarization and repolarization of rainbow trout (Oncorhynchus mykiss) ventricle

المجلة: Journal of Experimental Biology

سنة النشر: 2022

تاريخ النشر: 2022-09-02

The spatial pattern of electrical activation is crucial for a full understanding of fish heart function. However, it remains unclear whether there is regional variation in action potential (AP) morphologies and underlying ion currents. Because the direction of depolarization and spatial differences in the durations of ventricular APs set limits to potential patterns of ventricular repolarization, we determined AP morphologies, underlying ion currents and ion channel expression in four different ventricular regions (spongy myocardium; and apex, base and middle of the compact myocardium), and correlated them with in vivo electrocardiograms (ECGs) in rainbow trout (Oncorhynchus mykiss). ECGs recorded from three leads indicated that the depolarization and repolarization of APs propagate from base to apex, and the main depolarization axis of the ventricle is between +90 and +120 deg. AP shape was uniform across the whole ventricle, and little regional differences were found in the density of repolarizing K+ currents or depolarizing Ca2+ and Na+ currents and the underlying transcripts of ion channels, providing compelling evidence for the suggested excitation pattern. The spatial uniformity of AP durations and base-to-apex propagation of activation with a relatively slow velocity of propagation indicates no special ventricular conduction pathway in the trout ventricle such as the His–Purkinje system of mammalian hearts. The sequence of repolarization is solely determined by activation time without being affected by regional differences in AP duration.

Effects of seasonal acclimatization on thermal tolerance of inward currents in roach (Rutilus rutilus) cardiac myocytes

المجلة: Journal of Comparative Physiology B

سنة النشر: 2017

تاريخ النشر: 2017-09-23

To test the hypothesis of temperature-dependent deterioration of electrical excitability (TDEE) (Vornanen, J Exp Biol 219:1941–1952, 2016), the role of sodium (I Na) and calcium (I Ca) currents in heat tolerance of cardiac excitability was examined in a eurythermic fish, the roach (Rutilus rutilus). Densities of cardiac I Ca and I Na and their acute heat tolerance were measured in winter-acclimatized (WiR) and summer-acclimatized (SuR) fish maintained in the laboratory at 4 ± 1 and 18 ± 1 °C, respectively. A robust L-type Ca2+ current (I CaL), but no T-type Ca2+ current, was present in roach atrial and ventricular myocytes. Peak density of I CaL was smaller in atrial (− 1.97 ± 0.14 and − 1.75 ± 0.19 pA/pF for WiR and SuR, respectively) than ventricular myocytes (− 4.00 ± 0.59 and − 2.88 ± 0.47 pA/pF for WiR and SuR, respectively) (p < 0.05), but current density and heat tolerance of I CaL did not change between seasons in either cell type. In contrast to I Ca, marked differences appeared in I Na between WiR and SuR. I Na density was 38% higher in WiR than SuR atrial myocytes (− 80.03 ± 5.92 vs. − 49.77 ± 4.72 pA/pF; p < 0.05) and 48% higher in WiR than SuR ventricular myocytes (− 39.25 ± 3.06 vs. − 20.03 ± 1.79 pA/pF; p < 0.05). The winter increase in I Na density was associated with 55% (1.70 ± 0.27 vs. 0.77 ± 0.12) and 54% (1.08 ± 0.19 vs. 0.50 ± 0.10) up-regulation of the total Na+ channel (scn4 + scn5 + scn8) transcripts in atrium and ventricle, respectively (p < 0.05). Heat tolerance of atrial I Na was lower in WiR with a breakpoint temperature of 20.3 ± 1.2 °C than in SuR (23.8 ± 0.7 °C) (p < 0.05). The response of I Na to seasonal acclimatization conforms to the TDEE hypothesis. The lower heat tolerance of I Na in WiR is consistent with the lower heat tolerance of in vivo heart rate in WiR in comparison to SuR, but the match is not quantitatively perfect, suggesting that other factors in addition to I Na may be involved.

Tissue-specific differences and temperature-dependent changes in Na, K-ATPase of the roach (Rutilus rutilus)

المجلة: Aquaculture

سنة النشر: 2023

تاريخ النشر: 2023-01-30

Na,K-ATPase activity is vital for virtually all cells of the animal body and the major consumer of cellular energy. However, Na,K-ATPase activity, the number of Na+ pump units, the catalytic rate of the pump, and their responses to thermal acclimation in different tissues of the same fish species have been seldom measured. Therefore, roach (Rutilus rutilus), eurythermal freshwater fish, was acclimated at 4 °C (cold-acclimated, CA) and 18 °C (warm-acclimated, WA), and the Na+ pump density and the temperature-dependence of Na,K-ATPase activity were determined in the heart, gills, kidney and brain. There were prominent tissues specific differences in Na,K-ATPase activity. The activity was highest in the brain (100%), whereas the activity of renal, branchial and cardiac enzymes was 55%, 9%, and 4% of the brain activity in the WA roach at 25 °C. The corresponding values for brain, kidney, gills and heart of the CA fish at 25 °C were 100%, 56%, 5% and 4%, respectively. The number of Na,K-ATPase α-subunits, determined by [3H]ouabain binding, strongly correlated with the Na,K-ATPase activity at R2 values of 0.99 and 0.85 for WA and CA fish, respectively. Acclimation to cold, increased the number of Na,K-ATPase α-subunits in the heart, kidney and brain (P < 0.05), but this did not appear as an increase in Na,K-ATPase activity. In the gills, Na,K-ATPase α-subunits did not change in cold-acclimation, but Na,K-ATPase activity was depressed. Although tissue-specific differences in Na,K-ATPase activity are largely determined by the density of α-subunits, differences in Na,K-ATPase activity within the same tissue due to temperature acclimation involve also other factors in addition to the number of Na+ pump units.

Effects of seasonal acclimatization on action potentials and sarcolemmal K+ currents in roach (Rutilus rutilus) cardiac myocytes

المجلة: Comparative Biochemistry and Physiology Part A

سنة النشر: 2017

تاريخ النشر: 2017-03-01

Temperature sensitivity of electrical excitability is a potential limiting factor for high temperature tolerance of ectotherms. The present study examines whether heat resistance of electrical excitability of cardiac myocytes is modified by seasonal thermal acclimatization in roach (Rutilus rutilus), a eurythermal teleost species. To this end, temperature dependencies of ventricular action potentials (APs), and atrial and ventricular K+ currents were measured from winter-acclimatized (WiR) and summer-acclimatized (SuR) roach. Under patch-clamp recording conditions, ventricular APs could be triggered over a wide range of temperatures (4–43 °C) with prominent changes in resting membrane potential (RMP), AP duration and amplitude. In general, APs of SuR were slightly more tolerant to high temperatures than those of WiR, e.g. the break point temperature (TBP) of RMP was 37.6 ± 0.4 °C in WiR and 41 ± 1 °C in SuR (p < 0.05). Of the two major cardiac K+ currents, the inward rectifier K+ current (IK1) was particularly heat resistant in both SuR (TBP 39.4 ± 0.4 °C) and WiR (TBP 40.0 ± 0.4 °C) ventricular myocytes. The delayed rectifier K+ current (IKr) was not as heat resistant as IK1. Surprisingly, IKr of WiR tolerated heat better (TBP 31.9 ± 0.8 °C) than IKr of SuR (TBP 24.1 ± 0.5 °C) (p < 0.05). IKr (Erg2) channel transcripts of both atrial and ventricular myocytes were up-regulated in WiR. IK1 (Kir2) channel transcripts were not affected by seasonal acclimatization, although ventricular IK1 current was up-regulated in summer. Collectively, these findings show that thermal tolerance limits of K+ currents in isolated myocytes between seasonally acclimatized roach are much less pronounced than the heat sensitivity of ECG variables in intact fish.

Cardiac toxicity of cadmium involves complex interactions among multiple ion currents in rainbow trout (Oncorhynchus mykiss) ventricular myocytes

المجلة: Environmental Toxicology and Chemistry

سنة النشر: 2021

تاريخ النشر: 2021-07-13

Cadmium (Cd2+) is cardiotoxic to fish, but its effect on the electrical excitability of cardiac myocytes is largely unknown. To this end, we used the whole-cell patch-clamp method to investigate the effects of Cd2+ on ventricular action potentials (APs) and major ion currents in rainbow trout (Oncorhynchus mykiss) ventricular myocytes. Trout were acclimated to +4 °C, and APs were measured at the acclimated temperature and elevated temperature (+18 °C). Cd2+ (10, 20, and 100 µM) altered the shape of the ventricular AP in a complex manner. The early plateau fell to less positive membrane voltages, and the total duration of AP prolonged. These effects were obvious at both +4 °C and +18 °C. The depression of the early plateau is due to the strong Cd2+-induced inhibition of the L-type calcium (Ca2+) current (ICaL), whereas the prolongation of the AP is an indirect consequence of the ICaL inhibition: at low voltages of the early plateau, the delayed rectifier potassium (K+) current (IKr) remains small, delaying repolarization of AP. Cd2+ reduced the density and slowed the kinetics of the Na+ current (INa) but left the inward rectifier K+ current (IK1) intact. These altered cellular and molecular functions can explain several Cd2+-induced changes in impulse conduction of the fish heart, for example, slowed propagation of the AP in atrial and ventricular myocardia (inhibition of INa), delayed relaxation of the ventricle (prolongation of ventricular AP duration), bradycardia, and atrioventricular block (inhibition of ICaL). These findings indicate that the cardiotoxicity of Cd2+ in fish involves multiple ion currents that are directly and indirectly altered by Cd2+. Through these mechanisms, Cd2+ may trigger cardiac arrhythmias and impair myocardial contraction. Elevated temperature (+18 °C) slightly increases Cd2+ toxicity in trout ventricular myocytes.

Deltamethrin and retene toxicity to excitability of ventricular myocytes in rainbow trout (Oncorhynchus mykiss)

المجلة: Sohag Journal of Sciences

سنة النشر: 2023

تاريخ النشر: 2023-05-01

Pyrethroids such as deltamethrin are widely used to control insect pests. Due to their selective toxicity to insects, they are considered harmless to birds and mammals. On the other hand, polycyclic aromatic hydrocarbons (PAHs) such as retene are widespread contaminants in aquatic ecosystems and more problematic to endothermic vertebrates. Both pyrethroids and PAHs might affect the developmental and functional processes in the cardiovascular system of fish. Therefore, deltamethrin and retene toxicity to the electrical excitability of ventricular myocytes were examined in the Oncorhynchus mykiss (rainbow trout) heart. Micromolar concentrations of deltamethrin and retene modified the action potential (AP) morphology in a time-dependent manner. After 5 min of application, both compounds strongly prolonged AP duration (APD) compared to control AP. However, deltamethrin prolonged APD by 42% and 25% more than retene at APD50 and APD90, respectively. In contrast, retene reduced APD10 and the AP depolarization rate (+dV dt-1) by 61% and 12% more than deltamethrin, respectively. Although deltamethrin and retene changed the ventricular AP shape in rainbow trout in the same way, their mechanism of action seems to be different. The findings revealed that deltamethrin mainly affects the outward potassium currents, while retene mainly affects the inward sodium and calcium currents. Further studies are needed to reveal the underlying ion currents/channels that might be involved in the AP attenuation of rainbow trout under the effect of deltamethrin and retene.

Electrical excitability of roach (Rutilus rutilus) ventricular myocytes: effects of extracellular K+, temperature, and pacing frequency

المجلة: American Journal of Physiology

سنة النشر: 2018

تاريخ النشر: 2018-08-20

Exercise, capture, and handling stress in fish can elevate extracellular K+ concentration ([K+]o) with potential impact on heart function in a temperature- and frequency-dependent manner. To this end, the effects of [K+]o on the excitability of ventricular myocytes of winter-acclimatized roach (Rutilus rutilus) (4 ± 0.5°C) were examined at different test temperatures and varying pacing rates. Frequencies corresponding to in vivo heart rates at 4°C (0.37 Hz), 14°C (1.16 Hz), and 24°C (1.96 Hz) had no significant effect on the excitability of ventricular myocytes. Acute increase of temperature from 4 to 14°C did not affect excitability, but a further rise to 24 markedly decreased excitability: stimulus current and critical depolarization needed to elicit an action potential (AP) were ~25 and 14% higher, respectively, at 24°C than at 4°C and 14°C (P < 0.05). This depression could be due to temperature-related mismatch between inward Na+ and outward K+ currents. In contrast, an increase of [K+]o from 3 to 5.4 or 8 mM at 24°C reduced the stimulus current needed to trigger AP. However, other aspects of excitability were strongly depressed by high [K+]o: maximum rate of AP upstroke and AP duration were drastically (89 and 50%, respectively) reduced at 8 mM [K+]o in comparison with 3 mM (P < 0.05). As an extreme case, some myocytes completely failed to elicit all-or-none AP at 8 mM [K+]o at 24°C. Also, amplitude and overshoot of AP were reduced by elevation of [K+]o (P < 0.05). Although high [K+]o antagonizes the negative effects of high temperature on excitation threshold, the precipitous depression of the rate of AP upstroke and complete loss of excitability in some myocytes suggest that the combination of high temperature and high [K+]o will severely impair ventricular excitability in roach.

Dual effect of polyaromatic hydrocarbons on sarco (endo) plasmic reticulum calcium ATPase (SERCA) activity of a teleost fish (Oncorhynchus mykiss)

المجلة: Comparative Biochemistry and Physiology Part C

سنة النشر: 2024

تاريخ النشر: 2024-02-01

Polycyclic aromatic hydrocarbons (PAHs) are embryo- and cardiotoxic to fish that might be associated with improper intracellular Ca2+ management. Since sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) is a major regulator of intracellular Ca2+, the SERCA activity and the contractile properties of rainbow trout (Oncorhynchus mykiss) ventricle were measured in the presence of 3- and 4-cyclic PAHs. In unfractionated ventricular homogenates, acute exposure of SERCA to 0.1–1.0 μM phenanthrene (Phe), retene (Ret), fluoranthene (Flu), or pyrene (Pyr) resulted in concentration-dependent increase in SERCA activity, except for the Flu exposure, with maximal effects of 49.7–83 % at 1 μM. However, PAH mixture did not affect the contractile parameters of trout ventricular strips. Similarly, all PAHs, except Ret, increased the myotomal SERCA activity, but with lower effect (27.8–40.8 % at 1 μM). To investigate the putative chronic effects of PAHs on SERCA, the atp2a2a gene encoding trout cardiac SERCA was expressed in human embryonic kidney (HEK) cells. Culture of HEK cells in the presence of 0.3–1.0 μM Phe, Ret, Flu, and Pyr for 4 days suppressed SERCA expression in a concentration-dependent manner, with maximal inhibition of 49 %, 65 %, 39 % (P < 0.05), and 18 % (P > 0.05), respectively at 1 μM. Current findings indicate divergent effects of submicromolar PAH concentrations on SERCA: stimulation of SERCA activity in acute exposure and inhibition of SERCA expression in chronic exposure. The depressed expression of SERCA is likely to contribute to the embryo- and cardiotoxicity of PAHs by depressing muscle function and altering gene expression.

Three steps down: metabolic depression in winter-acclimatized crucian carp (Carassius carassius L.)

المجلة: Comparative Biochemistry and Physiology Part A

سنة النشر: 2024

تاريخ النشر: 2024-01-01

Acclimatization of certain ectothermic vertebrates to winter conditions is associated with reduced energy consumption (winter dormancy). Principally, this may be achieved by reducing movement activity, depression of basal cellular functions, or by switching from aerobic to anaerobic energy production to sustain low energy consumption during anoxia. Therefore, we determined standard (SMR), routine (RMR) and anoxic (AMR) metabolic rates in summer- (SumA; 20 °C) and winter-acclimatized (WinA; 2 °C) crucian carp (Carassius carassius), an anoxia-tolerant teleost fish. At 20 °C, RMR was 39% lower in WinA than SumA fish (p < 0.05), indicating reduced movements in winter. SMR, measured for the first time in crucian carp, was 45% lower in WinA than SumA fish at 10 °C (p < 0.05), indicating significant reduction of energy consumption in vital cellular processes. At 2 °C, AMR - measured from ethanol production- was 78% and 97% of the SMR and RMR levels at the same temperature, respectively. The current study revealed that the winter dormancy in anoxia-tolerant crucian carp is achieved in 3 different steps: (1) by active reduction of SMR, possibly in anticipation of seasonal anoxia, (2) acute Arrhenius Q10 effect that slows SMR as well as RMR, and (3) direct response to the absence of oxygen (AMR). Furthermore, the anoxic energy production was strongly dependent on body mass with scaling exponents of −0.335 and − 0.421 for WinA and SumA fish, respectively.

Effect of changes in temperature on the force–frequency relationship in the heart of catfish (Clarias gariepinus)

المجلة: The Journal of Basic & Applied Zoology

سنة النشر: 2012

تاريخ النشر: 2012-10-01

An isometric ventricular preparation was used to investigate the effect of changes in temperature (10, 15, 20, 25 and 30 °C) on the cardiac contractility produced by increasing of frequency in the catfish heart. The ability of the ventricular preparation to develop the cardiac force at 10 °C continued regularly until a frequency of 1.0 Hz, whereas at 15, 20, 25 and 30 °C, it continued developing the cardiac force until 2.0 Hz. The contractile force, the rate of contraction and the rate of relaxation (cardiac contractions) decreased significantly as contraction frequency increased. The decreases in the cardiac contractility with the increasing of the contraction frequency from 0.2 to 2.0 Hz were significantly higher at 15, 20 and 25 °C than that at the same frequency at 30 °C and at 10 °C in the range of frequency between 0.2 and 1.0 Hz. The percentage changes in the contractile force at a contraction frequency of 2.0 Hz at 15, 20 and 25 °C were 42 ± 2.7, 32 ± 2.5 and 32 ± 3.3, respectively; whereas it was 61 ± 1.3 at 30 °C, and at 10 °C, it was 60 ± 1.1 at a frequency of 1.0 Hz. So, it can be concluded that the catfish myocardium, like most fish hearts exhibits a negative force–frequency relationship. But, this relationship is highly affected by the changes in the temperature in a way that the lower temperature (10 °C) and the higher temperature (30 °C), may provide a protective mechanism against the depressive effects of higher stimulation frequency. This may be due to the differences in the handling of the activator Ca2+ to the contractile system via the transsarcolemmal Ca2+ channels and/or Na+–Ca2+ changes, and the sarcoplasmic reticulum Ca2+ release.

Temperature dependence of cardiac sarcoplasmic reticulum and sarcolemma in the ventricle of catfish (Clarias gariepinus)

المجلة: The Journal of Basic & Applied Zoology

سنة النشر: 2015

تاريخ النشر: 2015-10-01

The present study was undertaken to examine the relative contribution of the SR-Ca2+ release and sarcolemmal Ca2+ channels in developing the cardiac force at two different temperatures (20 and 30 °C) in the catfish (Clarias gariepinus). The sarcolemmal Ca2+ contribution of activator Ca2+ was greater at a test temperature of 30 °C as assessed by verapamil. Whereas the SR-Ca2+ contribution was higher at 20 and 30 °C and a frequency rate of 0.2 and 0.4 Hz as assessed by caffeine and adrenaline, respectively. Bradykinin potentiating factor (BPF7) which was isolated from jelly fish (Cassiopea andromeda) decreased the cardiac force developed at a frequency rate of 0.2 Hz and a temperature of 20 °C, whereas it increased the force developed at frequency rates of 0.2 and 0.4 Hz at 30 °C. These results indicate that BPF7 may act like verapamil in reducing the cardiac force through blocking the sarcolemmal Ca2+ channels at low temperature and like adrenaline in an increase of the cardiac force developed at warm temperature and the high frequency rate through stimulation of SR-Ca2+ activator. Therefore, this study indicates that the sarcolemmal Ca2+ influx and the SR-Ca2+ release contributors of activator Ca2+ for cardiac force development in the catfish heart were significantly greater at warm temperature and at the pacing frequency rates of 0.2 and 0.4 Hz as assessed by verapamil, adrenaline, caffeine and BPF7. However, the relative contribution of the sarcolemmal Ca2+ influx in the development of cardiac force in the catfish heart was greater than that of SR-Ca2+ release.