Effects of Ca2+ on ileal transport and electrically induced secretion

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Abstract
Ca2+ affects nerves and target cells in stimulus-secretion coupling. In flux-chamber studies of full-thickness rabbit ileum, the effects of ethylene glycol bis(.beta.-aminoethylether)-N,N''-tetraacetic acid (EGTA) 1.25 mM, verapamil 0.1 mM and nifedipine 0.1 mM and trifluoperazine 0.1 mM on ion transport and its response to electrical field stimulation (EFS) were determined. EGTA increased .**GRAPHIC**. [unidirectional movement of Cl from mucosal to serosal fluid] .**GRAPHIC**. Cl absorption, and conductivity (G) and reduced Isc [short circuit current]. In the absence of EGTA, EFS increased transmural PD [potential difference] and Isc and caused secretion of Na and Cl. EGTA prevented the responses to EFS, but the Isc responses to aminophylline and to glucose were normal. Verapamil reduced the response of Isc and Cl transport to EFS. Nifedipine-reduced Isc but not the Isc response to EFS. Trifluoperazine reduced Isc and almost eliminated the Isc response to EFS. EFS did not increase the tissue concentration of cAMP. Low extracellular [Ca2+] enhances net Cl absorption; extracellular Ca2+ is required for the response of ion transport to EFS; cAMP does not mediate Isc response to EFS and Isc response to EFS is blocked by trifluoperazine were concluded. EFS stimulates secretion by apparently increasing Ca entry into the epithelial cells, directly or indirectly.