Actin cytoskeletons regulate the stretch-induced increase of Ca2+ current in human gastric myocytes

Using the whole-cell and single channel recording techniques, the influence of actin cytoskeletons on L-type Ca2+ current was investigated in human gastric smooth muscle cells. In isotonic condition, an actin depolymerizer cytochalasin D (Cyt-D) markedly decreased the whole-cell current (IBa) without changing steady-state voltage dependency and single channel conductance. Intracellular dialysis of phalloidin, an actin polymerizer, significantly increased the IBa. Hypotonic stretch (222 mOsm/L) of the myocytes increased the IBa, and Cyt-D significantly inhibited the IBa increase by the stretch. Phalloidin was without effect on the IBa increase by the stretch. Phalloidin antagonized the Cyt-D inhibition of the stretch-induced IBa increase. Neither heterotrimeric G protein modifiers (GTPγS and GDPβS) nor rho GTPase inhibitor (C3 exoenzyme) influenced the stretch-induced responses. These results reveal that the integrity of the actin cytoskeleton is an important factor which determines the activity of L-type Ca2+ channels and a response to stretch.