Modulation of membrane potential by an acetylcholine-activated potassium current in trout atrial myocytes

Molina, Cristina E.; Gesser, H.; Llach, Anna; Tort, L.; Hove‐Madsen, Leif

doi:10.1152/ajpregu.00499.2005

Cited by 18 publications

(15 citation statements)

References 33 publications

(46 reference statements)

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“…This, combined with a strong similarity between teleost and human action potential morphology [26], [37], [46] (as opposed to the short and triangular shaped action potentials of murine cardiomyocytes), the robustness of isolated teleost cardiomyocytes, and the availability of morpholino antisense oligonucleotides in zebrafish, proposes the teleost heart as a relevant model to study genetic impact on SR function and cardiac arrhythmogenesis.…”

Section: Discussionmentioning

confidence: 99%

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Detection, Properties, and Frequency of Local Calcium Release from the Sarcoplasmic Reticulum in Teleost Cardiomyocytes

et al. 2011

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Calcium release from the sarcoplasmic reticulum (SR) plays a central role in the regulation of cardiac contraction and rhythm in mammals and humans but its role is controversial in teleosts. Since the zebrafish is an emerging model for studies of cardiovascular function and regeneration we here sought to determine if basic features of SR calcium release are phylogenetically conserved. Confocal calcium imaging was used to detect spontaneous calcium release (calcium sparks and waves) from the SR. Calcium sparks were detected in 16 of 38 trout atrial myocytes and 6 of 15 ventricular cells. The spark amplitude was 1.45±0.03 times the baseline fluorescence and the time to half maximal decay of sparks was 27±3 ms. Spark frequency was 0.88 sparks µm−1 min−1 while calcium waves were 8.5 times less frequent. Inhibition of SR calcium uptake reduced the calcium transient (F/F0) from 1.77±0.17 to 1.12±0.18 (p = 0.002) and abolished calcium sparks and waves. Moreover, elevation of extracellular calcium from 2 to 10 mM promoted early and delayed afterdepolarizations (from 0.6±0.3 min−1 to 8.1±2.0 min−1, p = 0.001), demonstrating the ability of SR calcium release to induce afterdepolarizations in the trout heart. Calcium sparks of similar width and duration were also observed in zebrafish ventricular myocytes. In conclusion, this is the first study to consistently report calcium sparks in teleosts and demonstrate that the basic features of calcium release through the ryanodine receptor are conserved, suggesting that teleost cardiac myocytes is a relevant model to study the functional impact of abnormal SR function.

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Section: Discussionmentioning

confidence: 99%

“…Action potentials and afterdepolarizations were recorded using the current-clamp technique and experimental protocols and conditions previously described [26]. Spontaneous membrane depolarizations were only considered afterdepolarizations if they were associated with a concurrent cell shortening.…”

Section: Methodsmentioning

confidence: 99%

Detection, Properties, and Frequency of Local Calcium Release from the Sarcoplasmic Reticulum in Teleost Cardiomyocytes

et al. 2011

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“…However, it is tempting to speculate that the known suppression of turtle cholinergic cardiac tone with cold acclimation (20) plays an important role. In rainbow trout atrial myocytes, acetylcholine activates inwardly rectifying K ϩ currents and stabilizes RMP at more negative voltages (38). Therefore, if a similar phenomenon exists for turtle cardiomyocytes, it is conceivable that the absence of turtle cardiac cholinergic tone with cold acclimation allows for the decreased I K1 , the less negative RMP, and the potential for control of I K1 by other mechanisms.…”

Section: Modification Of Turtle Heart Electrophysiology With Cold Temmentioning

confidence: 95%

Effect of temperature and prolonged anoxia exposure on electrophysiological properties of the turtle (Trachemys scripta) heart

Stecyk¹,

Paajanen²,

Farrell³

et al. 2007

American Journal of Physiology-Regulatory, Integrative and Comp

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Cardiac activity of the turtle (Trachemys scripta) is greatly depressed with cold acclimation and anoxia. We examined what electrophysiological modifications accompany and perhaps facilitate this depression of cardiac activity. Turtles were first acclimated to 21 degrees C or 5 degrees C and held under either normoxic or anoxic (6 h at 21 degrees C; 14 days at 5 degrees C) conditions. We then measured cardiac action potentials (APs) using spontaneously contracting whole heart preparations and whole cell current densities of sarcolemmal ion channels using isolated ventricular myocytes under appropriate normoxic and anoxic conditions. Compared with 21 degrees C-acclimated turtles, 5 degrees C-acclimated turtles exhibited a less negative resting membrane potential (by 18-29 mV), a 4.7- to 6.8-fold slower AP upstroke rate, and a 4.2- to 4.9-fold greater AP duration. Correspondingly, peak densities of ventricular voltage-gated Na(+) (I(Na)) and L-type Ca(2+) currents and inward slope conductances of inward rectifier K(+) (I(K1)) channel current were approximately 1/7th (Q(10) = 3.4), 1/13th (Q(10) = 5.0), and one-half (Q(10) = 1.4) of those of 21 degrees C-acclimated ventricular myocytes, respectively. With anoxia at 21 degrees C, peak I(Na) density doubled and ventricular AP duration increased by 47%, a change proportional to the reported approximately 30% reduction of intrinsic heart rate. In contrast, with anoxia at 5 degrees C, ventricular AP characteristics were unaffected; of the ion currents investigated, only the inward conductance via I(K1) changed significantly (reduced by 46%). The present findings indicate that cold temperature, more so than prolonged anoxia, results in substantial modifications of cardiac APs and reduction of ventricular ion current densities. These changes likely prepare cardiac muscle for winter anoxia conditions.

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“…T wave A wave of an ECG that is generated by ventricular repolarization. (Talo and Tirri, 1991;Vornanen, 1996;Molina et al, 2007;Haverinen and Vornanen, 2009;Galli et al, 2009;Ballesta et al, 2012). This rapid voltage change is produced by the opening of Na + channels, which generate the inward Na + current (I Na ).…”

Section: Threshold Potentialmentioning

confidence: 99%

The temperature dependence of electrical excitability in fish hearts

Vornanen

2016

Journal of Experimental Biology

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Environmental temperature has pervasive effects on the rate of life processes in ectothermic animals. Animal performance is affected by temperature, but there are finite thermal limits for vital body functions, including contraction of the heart. This Review discusses the electrical excitation that initiates and controls the rate and rhythm of fish cardiac contraction and is therefore a central factor in the temperature-dependent modulation of fish cardiac function. The control of cardiac electrical excitability should be sensitive enough to respond to temperature changes but simultaneously robust enough to protect against cardiac arrhythmia; therefore, the thermal resilience and plasticity of electrical excitation are physiological qualities that may affect the ability of fishes to adjust to climate change. Acute changes in temperature alter the frequency of the heartbeat and the duration of atrial and ventricular action potentials (APs). Prolonged exposure to new thermal conditions induces compensatory changes in ion channel expression and function, which usually partially alleviate the direct effects of temperature on cardiac APs and heart rate. The most heat-sensitive molecular components contributing to the electrical excitation of the fish heart seem to be Na + channels, which may set the upper thermal limit for the cardiac excitability by compromising the initiation of the cardiac AP at high temperatures. In cardiac and other excitable cells, the different temperature dependencies of the outward K + current and inward Na + current may compromise electrical excitability at temperature extremes, a hypothesis termed the temperature-dependent depression of electrical excitation.

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Modulation of membrane potential by an acetylcholine-activated potassium current in trout atrial myocytes

Cited by 18 publications

References 33 publications

Detection, Properties, and Frequency of Local Calcium Release from the Sarcoplasmic Reticulum in Teleost Cardiomyocytes

Detection, Properties, and Frequency of Local Calcium Release from the Sarcoplasmic Reticulum in Teleost Cardiomyocytes

Effect of temperature and prolonged anoxia exposure on electrophysiological properties of the turtle (Trachemys scripta) heart

The temperature dependence of electrical excitability in fish hearts

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