Cell Cycle-Dependent Expression of L- and T-Type Ca 2+ Currents in Rat Aortic Smooth Muscle Cells in Primary Culture

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Abstract
The expression of L- and T-type Ca2+ channels has been reported to change during various biological events, including cellular differentiation and proliferation. The present study aimed to examine whether or not the expression of L- and T-type Ca2+ channels depends on the cell cycle in rat aortic smooth muscle cells in primary culture. Both the phase of the cell cycle and the functional expression of Ca2+ channels were determined in the same single cell, using an immunocytochemical analysis of cell cycle-specific nuclear antigens and a whole-cell voltage-clamp method, respectively. In the G0 (n=130) and M (n=75) phases, all cells showed only L-type Ca2+ currents. The cells showing a T-type Ca2+ current appeared in the G1 phase (37%, n=85) and increased in the S phase (90%, n=21). For L-type Ca2+ channels, the current density was significantly greater in the G1 phase than in the G0 and M phases. However, either the voltage-dependent properties or the dose-response relationships of Bay K 8644- and second me...