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

Submucosal interstitial cells of Cajal (ICCSM) produce plateau potentials comprised of initial fast and subsequent plateau components. The possible involvement of voltage-dependent Ca2+ channels in plateau potentials was examined in ICCSM 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 15.3 mM [K+]o and a decrease in 20.0 mM [K+]o. The rise rate of plateau potentials was significantly reduced by the application of 3 μM mibefradil or 100 μM Ni2+ but not by 0.3 μM nifedipine. The inhibitory effect of mibefradil on the rise rate of plateau potentials was concentration-dependent with an IC50 value of 1.0 μM. In conclusion, the initial phase of plateau potentials is partly due to the activation of T-type Ca2+ channel in ICCSM from the murine proximal colon.