Properties of human atrial ICa at physiological temperatures and relevance to action potential.

There are no published characterizations of Ca2+ current (ICa) at physiological temperatures in human atrium. Depolarization of human atrial myocytes at 36 degrees C elicited ICa that peaked at +10 mV, with a mean maximum current density of 10.8 +/- 1.1 pA/pF and no evidence for T-type current. Overlap between activation and inactivation curves and incomplete inactivation during pulses comparable to normal action potential duration (APD) were compatible with the observed role of ICa in maintaining the plateau. ICa was frequency dependent between 0.1 and 2 Hz and ICa blockade with 0.2 mM Cd2+ reduced rate-dependent changes in APD: under control, APD at 90% repolarization was 230 +/- 15 ms at 0.1 Hz and 178 +/- 14 ms at 2 Hz (decrease of 52 +/- 5 ms); with Cd2+, values were 121 +/- 7 ms at 0.1 H2 and 115 +/- 6 ms at 2 Hz (decrease of 6 +/- 3 ms, P < 0.01) Isoproterenol (1 microM) increased ICa and prolonged APD from 138 +/- 13 to 199 +/- 15 ms (P < 0.01). These results indicate that, in human atrial cells at 36 degrees C, the properties of L-type ICa contribute importantly to the rate-dependent and autonomic control of APD.