Modes of Cl- transport across the mucosal and serosal membranes of urodele intestinal cells.

Abstract

The characteristics of Cl- movement across luminal and basolateral membranes of Amphiuma intestinal absorptive cells were studied using Cl(-)-sensitive microelectrodes and tracer 36Cl techniques. Intracellular Cl- activity (aiCl) was unchanged when serosal Cl- was replaced; when luminal Cl- was replaced cell Cl- was rapidly lost. Accordingly, the steady state aiCl could be varied by changing the luminal [Cl]. As luminal [Cl] was raised from 1 to 86 mM, aiCl rose in a linear manner, the mucosal membrane hyperpolarized, and the transepithelial voltage became serosa negative. In contrast, the rate of Cl- transport from the cell into the serosal medium, measured as the SITS-inhibitable portion of the Cl- absorptive flux, attained a maximum when aiCl reached an apparent value of 17 mM, indicating the presence of a saturable, serosal transport step. The stilbene-insensitive absorptive flux was linear with luminal [Cl], suggestive of a paracellular route of movement. Intracellular aCl was near electrochemical equilibrium at all but the lowest values of luminal [Cl] after interference produced by other anions was taken into account. aiCl was unaffected by Na replacement, removal of medium K, or elevation of medium HCO-3. Mucosae labeled with 36Cl lost isotope into both luminal and serosal media at the same rate and from compartments of equal capacity. Lowering luminal [Cl] or addition of theophylline enhanced luminal Cl- efflux. It is concluded that a conductive Cl leak pathway is present in the luminal membrane. Serosal transfer is by a saturable, stilbene-inhibitable pathway. Luminal Cl- entry appears to be passive, but an electrogenic uptake cannot be discounted.