SLOW INACTIVATION OF CARDIAC L-TYPE CA2-ACCLIMATION OF GUINEA-PIG( CHANNEL INDUCED BY COLD)

Whole cell L-type Ca2+ current was recorded in ventricular myocytes di ssociated from guinea pigs that were bred at ambient temperatures rang ing between daily averages of 4 and 29 degrees C. The dynamic voltage range of inactivation, as measured using 400-ms conditioning pulses an d a holding potential of -40 mV, extended from -50 to -20 mV in myocyt es prepared in summer. In winter, the inactivation curve was shifted t o mofe negative potentials than in summer. Double-pulse experiments re vealed that the negative shift was due to slow-inactivation kinetics T he negative shift of inactivation could be induced in myocytes prepare d from animals that had been kept at 5 degrees C for >3 wk in the summ er. The negative shift in Ca2+ current inactivation could be abolished by adding guanosine 5'-O-(2-thiodiphosphate) (5 mM) to the pipette so lution, but not by adding staurosporine (2 mu M) or 1-(5-isoquinolinyl sulfonyl)-2-methylpiperazine (100 mu M) to the bath. The cold acclimat ion may introduce the slow inactivation of the cardiac L-type Ca2+ cha nnel through an unknown pertussis toxin-insensitive CT protein.