Calcium dependence of basal electrolyte transport in rabbit ileum

Abstract

The effect on active electrolyte transport of altering the Ca concentration in the fluid bathing the mucosal and serosal surfaces of rabbit ileum was studied in vitro using the Ussing chamber voltage-clamp technique. Ca-deprived (no-Ca) bathing solutions simultaneously placed on both the mucosal and the serosal surfaces decreased short-circuit current and potential difference, increased conductance, equally increased net Na and Cl- absorption, and decreased the residual ion flux. There was no effect on glucose-dependent Na absorption. These changes were constant for 150 min and, except for conductance, were reversed by replacing the bathing solutions with standard Ringer-HCO3 containing 1.2 mM Ca. These changes in transport were associated with a decrease in total ileal Ca content as measured by atomic absorption spectrometry. Adding the Ca channel blocker verapamil (10-4 M) to the solutions bathing the serosal plus mucosal surfaces of rabbit ileum or to the serosal surface alone duplicated these effects. The effect of the Ca deprived mucosal plus serosal bathing solutions on Na transport was prevented by removing Cl- from the bathing solutions; similarly, the effect on Cl- transport was abolished by removing Na from the bathing solutions. Evidently, lowering intracellular Ca is associated with stimulation of active ileal Na and Cl- absorption. This information must be combined with the previous demonstration that increasing intracellular Ca with agents such as serotonin inhibits Na and Cl- absorption. Ca may be a physiological regulator of active Na and Cl- transport in the ileum.