Mibefradil-sensitive component involved in the plateau potential in submucosal interstitial cells of the murine proximal colon.

Submucosal interstitial cells of Cajal (ICC(SM)) produce plateau potentials comprised of initial fast and subsequent plateau components. The possible involvement of voltage-dependent Ca(2+) channels in plateau potentials was examined in ICC(SM) of the murine proximal colon. Increases in external K(+) concentration ([K(+)](o)) changed the rise rate of the initial component in a biphasic way, an increase in 10.6 or 15.3mM [K(+)](o) and a decrease in 20.0mM [K(+)](o). The rise rate of plateau potentials was significantly reduced by the application of 3 microM mibefradil or 100 microM Ni(2+) but not by 0.3 microM nifedipine. The inhibitory effect of mibefradil on the rise rate of plateau potentials was concentration-dependent with an IC(50) value of 1.0 microM. In conclusion, the initial phase of plateau potentials is partly due to the activation of T-type Ca(2+) channel in ICC(SM) from the murine proximal colon.