Ca2+ utilization in guinea pig ileal longitudinal smooth muscle in response to a series of muscarinic agonists

Abstract

45Ca uptake associated with the mechanical responses to a series of muscarinic agonists including carbachol, cis-2-methyl-4-dimethylaminomethyl-1,3-dioxolane methiodide, and three related 1,3-dioxolanes, including full and partial agonists, has been measured. Generally good agreement is found between the dose–response curves for 45Ca uptake and mechanical response, indicating that the processes of 45Ca entry, believed to be mediated through Ca2+ channels, and contractile response are closely linked. Consistent with this, partial agonists show (relative to full agonists) a reduced 45Ca uptake. The dose–response curves for carbachol-mediated contractile response and 45Ca uptake are compared with available literature data for carbachol action in the guinea pig ileal smooth muscle including binding, depolarization, and phosphatidylinositol turnover.