Actin filament disruption inhibits L-type Ca2+ channel current in culturedvascular smooth muscle cells

To clarify interactions between the cytoskeleton and activity of L-type Ca2 + (Ca-L) channels in vascular smooth muscle (VSM) cells, we investigated th e effect of disruption of actin filaments and microtubules on the L type Ca 2+ current [I-Ba( L)] of cultured VSM cells (A7r5 cell line) using whole ce ll voltage clamp. The cells were exposed to each disrupter for 1 h and then examined electrophysiologically and morphologically. Results of immunostai ning using anti-alpha-actin and anti-alpha-tubulin antibodies showed that c olchicine disrupted both actin filaments and microtubules, cytochalasin D d isrupted only actin filaments, and nocodazole disrupted only microtubules. I-Ba(L) was greatly reduced in cells that were exposed to colchicine or cyt ochalasin D but not to nocodazole. Colchicine even inhibited I-Ba(L) by abo ut 40% when the actin filaments were stabilized by phalloidin or when the c ells were treated with phalloidin plus taxol to stabilize both cytoskeletal components. These results suggest that colchicine must also cause some inh ibition of I-Ba(L) due to another unknown mechanism, e.g., a direct block o f Ca-L channels. In summary, actin filament disruption of VSM cells inhibit s Ca-L channel activity, whereas disrupting the microtubules does not.