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

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.