Regulation of goby intestinal ion absorption by the calcium messenger system

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.