Cell cycle-dependent expression of L- and T-Type Ca2+ currents in rat aortic smooth muscle cells in primary culture

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 G(0) (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 G(1) 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 G(1) phase than in the G(0) and M phases. However, either the voltage-dependent properties or the dose-response relationships of Bay K 8641- and second messenger-induced modulations of L- type Ca2+ current did not differ in the four phases of the tell cycle. These findings thus indicate that the expression of L- and T-type Ca2+ channels depends on the cell cycle, whereas the characteristics of L-type Ca2+ channels do not differ between the phases of the cell cycle.