Interaction between aluminum and calcium ions in potassium chloride depolarized gastrointestinal smooth muscle

Aluminum chloride (5 times 10-minus 4 M) abolished the inhibitory effects of papaverine chloride (1.5 times 10- minus 5 M) on contractions of guinea-pig ileum and rat colon evoked by calcium in Tyrode's solution containing high KC1. The inhibitory effects of cocaine hydrochloride (10- minus 3 M) and MgSO4 (2 times 10- minus 2 M) were not antagonized. In isolated rat colon depolarized by partial exchange of NaCl by 40 mM KC1, AlC13 decreased the phasic contractions, slowed the onset of tonic contraction while increasing maximal tone and induced superimposed spontaneous activity during the tonic phase. Similar changes were evoked by increasing the CaCl2 concentration from 1.8 times 10- minus 3 M to 7.2 times 10- minus 3 M. The increase in spontaneous activity was not blocked by atropine sulfate (10- minus 7 minus 10- minus 4 M) but was partially antagonized by 10- minus 3 M caffeine and completely blocked by papaverine chloride (5 times 10- minus 4 M). More than one aluminum site of action is proposed for effects of aluminum on the gastro-intestinal smooth muscle.