Regulation of goby intestinal ion absorption by the calcium messenger system

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Abstract
The role of the calcium messenger system in the regulation of ion absorption across the teleost intestine was studied using pharmacological intervention. Radiochloride transport was independent of external Ca2+ over the range 10 μM to 2.5 mM. Treatment with the Ca2+ ionophore A23187 (to elevate intracellular Ca2+) reduced Cl− absorption and produced hyperpolarization of the apical membrane potential of intestinal epithelial cells. The Ca2+‐calmodulin antagonists trifluoperazine (TFP) and calmidazolium (R24571) produced opposite effects, i.e., stimulation of Cl− absorption and cellular depolarization. Treatment with TFP or R24571 will block or override the inhibitory action of A23187. These data suggest a regulatory role for Ca2+ in the control of intestinal NaCl absorption and mediation via calmodulin.