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Calcium mediation of the pig jejunal secretory response



Calcium mediation of the pig jejunal secretory response



Canadian Journal of Comparative Medicine 49(2): 179-185



The involvement of Ca2+ ions as secretory mediators in pig jejunal epithelia was investigated with an in vitro system. Omission of Ca2+ from the Ringer-HCO3 bathing media on both sides of the tissue had minor effects on the basal electrical activity of pig jejunal mucosa. There were only slight decreases in transepithelial potential difference and increases in conductance with Ca2+ free media. Low EGTA [ethylene glycol bis(.beta.-aminoethyl ether)N,N,N',N'-tetraacetic acid] concentrations which reversibly blocked potential difference responses to secretory agents also had minimal effects on basal electrical activity. The in vitro secretory responses to A23187 [calcimycin], to theophylline, and to Escherichia coli heat-stable enterotoxin were all eliminated by Ca2+ depletion and restored by replacing normal Ca2+ concentrations in the bathing media. Dantrolene prevented the secretory response but not the potential difference increases caused by heat-stable enterotoxin and A23187, suggesting that intracellular Ca2+ stores may be reservoirs of secretory signal agent. Verapamil only blocked the secretory response to heat-stable enterotoxin. Chlorpromazine had negligible effects on basal conditions, but totally blocked both the secretory response and the Ca2+-dependent effects of A23187 and heat-stable enterotoxin on potential difference. The response to theophylline was only partially inhibited by chlorpromazine, implying some involvement of both cAMP and Ca2+ as secretory signals for theophylline. Cytoplasmic Ca2+ concentrations appear to be at least as important as cyclic nucleotides in regulating the secretory effects of pig jejunum.

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Accession: 001311558

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PMID: 2410089


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