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

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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 3 related 1,3-dioxolanes [2,2-dimethyl-N,N-dimethylaminomethyl-1,3-dioxolane methiodide; 2,2-diethyl-N,N-dimethylaminomethyl-1,3-dioxolane methiodide; 2,2-diisopropyl-N,N-dimethylamino methyl-1,3-dioxolane methiodide], 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 isolated guinea pig ileal smooth muscle including binding, depolarization and phosphatidylinositol turnover.