Roles of molecular regions in determining differences between voltage dependence of activation of CaV3.1 and CaV1.2 calcium channels

Abstract

Voltage-dependent calcium channels are classified into low voltage-activated and high voltage-activated channels. We have investigated the molecular basis for this difference in voltage dependence of activation by constructing chimeras between a low voltage-activated channel (Ca V3.1) and a high voltage-activated channel (CaV1.2), focusing on steady-state activation properties. Wild type and chimeras were expressed in oocytes, and two-electrode voltage clamp recordings were made of calcium channel currents. Replacement of domains I, III, or IV of the Ca V3.1 channel with the corresponding domain of CaV1.2 led to high voltage-activated channels; for these constructs the current/voltage (I/V) curves were similar to those for CaV1.2 wild type. However, replacement of domain II gave only a small shift to the right of the I/V curve and modulation of the activation kinetics but did not lead to a high voltage-activating channel with an I/V curve like CaV1.2. We also investigated the role of the voltage sensor S4 by replacing the S4 segment of CaV3.1 with that of CaV1.2. For domain I, there was no shift in the I/V curve as compared with CaV3.1, and there were relatively small shifts to the right for domains III and IV. Taken together, these results suggest that domains I, III, and IV (rather than domain II) are apparently critical for channel opening and, therefore, contribute strongly to the difference in voltage dependence of activation between CaV3.1 and CaV1.2. However, the S4 segments in domains I, III, and IV did not account for this difference in voltage dependence.