Abstract
Rate-dependent alterations of action potential duration (APD) in rat ventricular myocytes were investigated. Action potentials of the isolated myocytes were recorded with patch electrodes containing EGTA (11 mM), and showed a marked rate-dependent prolongation in the APD (0.2–5 Hz). This prolongation was significantly inhibited in the presence of 4-aminopyridine (4-AP), a blocker of the transient outward K+ current (Ito). Thus, the rate-dependent decrease in Ito may underlie the change in APD. In contrast, the action potentials recorded from rat ventricular papillary muscles with conventional microelectrodes did not show rate-dependent alterations in the APD, i.e., the APD remained practically unaltered at the frequency range of 0.2–5 Hz. These results suggest that the rate-dependent prolongation of APD (due to rate-dependent blockade of Ito) becomes evident when the intracellular Ca2+ was chelated by the internal application of EGTA via patch pipette. We speculate that the rate-dependent prolongation of APD (via decreases in Ito) is masked in the ventricular papillary muscles, probably due to rate-dependent decreases in the inward current (e.g., electrogenic Na+−Ca2+ exchange current) that is regulated by the intracellular calcium.
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Shigematsu, S., Kiyosue, T., Sato, T. et al. Rate-dependent prolongation of action potential duration in isolated rat ventricular myocytes. Basic Res Cardiol 92, 123–128 (1997). https://doi.org/10.1007/BF00788629
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DOI: https://doi.org/10.1007/BF00788629