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

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Abstract
Summary The characteristics of Cl− movement across luminal and basolateral membranes ofAmphiuma intestinal absorptive cells were studied using Cl−-sensitive microelectrodes and tracer36Cl techniques. Intracellular Cl− activity (a iCl ) was unchanged when serosal Cl− was replaced; when luminal Cl− was replaced cell Cl− was rapidly lost. Accordingly, the steady statea iCl could be varied by changing the luminal [Cl]. As luminal [Cl] was raised from 1 to 86mM,a iCl 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 whena iCl reached an apparent value of 17mm, indicating the presence of a saturable, serosal transport step. The stilbeneinsensitive absorptive flux was linear with luminal [Cl], suggestive of a paracellular route of movement. Intracellulara Cl was near electrochemical equilibrium at all but the lowest values of luminal [Cl] after interference produced by other anions was taken into account.a iCl was unaffected by Na replacement, removal of medium K, or elevation of medium HCO −3 . Mucosae labeled with36Cl 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.