Repolarizing potassium currents in working myocardium of Japanese quail: a novel translational model for cardiac electrophysiology

Catecholamines are key modulators of ventricular repolarization patterns in the ball python (Python regius)

“…For ventricular repolarization of pythons to be similar to that of mammals, our study suggests that at least three conditions have to be met. First, there should be evolutionary conservation of the electrophysiological processes, and our RNA sequencing demonstrates a substantial evolutionary conservation on the transcript level, including of the major ion-handling channels, in agreement with previous studies ( Olson, 2006 ; Castoe et al, 2013 ; Duan et al, 2017 ; Filatova et al, 2021 ; Offerhaus et al, 2021 ). Second, catecholamines should augment differences in repolarization time between regions within the ventricle, and we find this to be the case in pythons.…”

Avian cardiomyocyte architecture and what it reveals about the evolution of the vertebrate heart

“…Excitation-contraction coupling in all vertebrate myocytes proceeds from the action potential. Atrial and ventricular action potential waveform and the corresponding repolarizing currents (I Kr , I Ks , I to ) have recently been characterized together for the first time in an adult bird (Japanese quail) [16]. Resting heart rates for these birds range between 318 and 530 beats min −1 [45,46] which is comparable to small rodents (mice/rats) and clearly depends on rapid/ early ventricular repolarization [17].…”

“…The large surface-area-to-volume ratio of the bird cardiomyocyte (table 1, figure 2 and [16,32]) means transsarcolemmal Ca 2+ influx can rapidly raise intracellular Ca 2+ levels in the periphery of the thin cardiomyocyte, in-line with observations from ectothermic vertebrates [39,53]. However, unlike most ectothermic vertebrates, excitation-contraction coupling in birds also relies heavily on SR Ca 2+ release [16,32] which amplifies the transsarcolemmal Ca 2+ signal through CICR leading to stronger faster contractions [32]. Ca 2+ diffusion is too slow to activate a coordinated and synchronized release of SR Ca 2+ across the wider mammalian myocyte [54].…”

“…The anatomical separation of left and right ventricles in birds and mammals allows the elevation of systemic pressure significantly above pulmonary pressure thereby providing the necessary convection for highly aerobic tissues, whilst avoiding the rupture of thin respiratory surfaces [12][13][14]. The presence of a specialized conduction system [15] and a compact atrial and ventricular wall architecture is important for the fast atrioventricular conduction and rapid ventricular repolarization [16,17] of avian and mammalian hearts compared with those of ectothermic vertebrates (independent of temperature) [14,15,18]. Indeed, the convergent evolution of rapid/ early repolarization in birds (zebrafinch) and mammals (mouse) is undoubtably important for achieving the fast heart rates typical of endotherms [17].…”

“… l Derived from cell length and width assuming an elliptical cross-sectional area. m Derived from cell capacitance (pF) following method of Vornanen [35]. n Coturnix japonica [16].

Figure 2Images of freshly isolated ventricular myocytes from ( a ) Japanese quail Coturnix japonica as light microscope image (top) [32] and an immunofluorescent image with sarcomeres delineated with a green probe to α-actinin and nucleus in red (bottom) [16], ( b ) varanid lizard Varanus exanthematicus light microscope image, arrow is pointing to sarcomeric striations (top) and confocal image with the sarcolemmal membrane visible in red (bottom) [30], ( c ) yellow-bellied turtle Trachemys scripta scripta light microscope image (top) and confocal image with the sarcolemmal membrane visible in red (bottom) [29].

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