Slow inactivation of cardiac L-type Ca21 channel induced by cold acclimation of guinea pig

Takagi, Shuichi, Yasuki Kihara, Shigetake Sasayama, and Tamotsu Mitsuiye. Slow inactivation of cardiac L-type Ca21 channel induced by cold acclimation of guinea pig. Am. J. Physiol. 274 (Regulatory Integrative Comp. Physiol. 43): R348–R356, 1998.—Whole cell L-type Ca21 current was recorded in ventricular myocytes dissociated from guinea pigs that were bred at ambient temperatures ranging between daily averages of 4 and 29°C. The dynamic voltage range of inactivation, as measured using 400-ms conditioning pulses and a holding potential of 240 mV, extended from 250 to 220 mV in myocytes prepared in summer. In winter, the inactivation curve was shifted to more negative potentials than in summer. Double-pulse experiments revealed that the negative shift was due to slow-inactivation kinetics. The negative shift of inactivation could be induced in myocytes prepared from animals that had been kept at 5°C for .3 wk in the summer. The negative shift in Ca21 current inactivation could be abolished by adding guanosine 58-O-(2-thiodiphosphate) (5 mM) to the pipette solution, but not by adding staurosporine (2 μM) or 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (100 μM) to the bath. The cold acclimation may introduce the slow inactivation of the cardiac L-type Ca21 channel through an unknown pertussis toxin-insensitive G protein.