Rapid-scanning confocal microscopy shows ventricular Ca2+ concentration becomes uniform within 10 ms via T-tubules, whereas atrial myocytes exhibit sequential subsarcolemmal to central Ca2+ release.
The study highlights fundamental atrio-ventricular differences in excitation-contraction coupling, explaining variations in their response to physiological and pharmacological stimuli.
Rapid-scanning cofocal microscopy has been applied to the analysis of early phase Ca2+ transients in ventricular and atrial cardiomyocytes. On electrical stimulation of ventricular myocytes, Ca2+ concentration begins to rise earliest at the Z-line level and becames uniform throughout the cytoplasm within about 10 ms after the onset of the action potential; transsarcolemmal Ca2+ influx triggers Ca2+ release from release sites on the junctional sarcoplasmic reticulum (SR) coupled to T-tubules at the Z-line throughout the cytoplasm. In atrial myocytes lacking the T-tubular network, transsarcolemmal Ca2+ influx during an action potential triggers SR Ca2+ release only at subsarcolemmal region. SR Ca2+ release then spreads towards the central region of the cell thourgh a propagated Ca2+-induced-Ca2+ release mechanism. The atrio-ventricular difference in excitation-contraction coupling mechanisms underlies some of the atrio-ventricular difference in response to physiological and pharmacological stimuli.
Tanaka et al. (Wed,) conducted a other in Myocardial Excitation-Contraction Coupling. Rapid-scanning confocal microscopy vs. Atrial vs ventricular cardiomyocytes was evaluated on Ca2+ transients and SR Ca2+ release mechanisms. Rapid-scanning confocal microscopy shows ventricular Ca2+ concentration becomes uniform within 10 ms via T-tubules, whereas atrial myocytes exhibit sequential subsarcolemmal to central Ca2+ release.