The effects of S4 segments on the voltage-dependence of inactivation for Cav3.1 calcium channels

T-type calcium channels exhibit fast voltage-dependent inactivation, for which the underlying structure-function relationship still remains unclear. To investigate the roles of S4 segments in voltage-dependent inactivation of T-type calcium channels, we created S4 replacement chimeras between Cav3.1 calcium channels (fast voltage-dependent inactivation) and Cav1.2 calcium channels (little voltage-dependent inactivation) by replacing S4s in Cav3.1 with the corresponding regions in Cav1.2. Wild type and chimeric channels were expressed in Xenopus oocytes and channel currents were recorded with two-electrode voltage-clamp. We showed that replacing S4 region in domain I shifted voltage-dependence for inactivation of Cav3.1 to the left, and the V-0.5inact and k(inact) value were significantly changed. However replacing Sits in domains II-IV had no effects on the voltage-dependent inactivation properties. These results suggest that the roles of S4 segments in domains I-IV are different, and S4 in domain I is likely to be involved in voltage-dependent inactivation process. Its movement during membrane depolarization may trigger a conformational change in the inactivation gate.