平滑筋における受容体作動性チャネル電流の特性とその制御機構

抄録

Stimulation of excitatory receptors in smooth muscle often leads to the opening of ROCC. These channels exhibit considerable permeability to Ca²⁺, and they have been regarded as the most probable candidate for the “receptor-operated Ca²⁺ entry” pathway. The muscarinic receptor ROCC in guinea pig ileum (mROCC) have a unitary conductance of ?? 25pS and are activated through a pertusis toxin-sensitive G protein. mROCC permeate Ca²⁺ and Ba²⁺ several fold more preferably than monovalent cations, and they are inhibited by various types of K channel blockers, diphenylamine-2-carboxylate derivatives and even by nicardipine and D-600 at high concentrations. mROCC are efficiently regulated by various physiological factors including the membrane potential, intracellular Ca²⁺ concentration, external pH and osmolarity. The effective ranges of these factors span their dynamic ranges under physiological conditions. In addition to these properties, mROCC have several sites sensitive to external polyvalent cations. The α₁-adrenergic receptor ROCC in rabbit portal vein resemble mROCC in many respects, e.g., the unitary conductance, ionic selectivity, activation kinetics, sensitivity to polyvalent cations and voltage-dependence. These complex characteristics of ROCC suggest that they play other roles in addition to being just a passive cation permeable pore in agonist-mediated Ca²⁺ mobilization in smooth muscle.