Cl^- channels in basolateral renal medullary vesicles IX. Channels from mouse MTAL cell patches and medullary vesicles

The experiments reported herein compared Cl^- channels fused into bilayers from rabbit outer medullary vesicles with Cl^- channels in excised patches of basolateral membranes from cultured mouse medullary thick ascending limb (MTAL) cells and evaluated whether the latter were plausible candidates for the Cl^- channels mediating net NaCl absorption in microperfused mouse MTAL segments. The unique signature characteristics of Cl^- channels incorporated into lipid bilayers from outer medullary vesicles include activation of open probability (P_o) by increases in the Cl^- concentrations bathing intracellular faces; activation of P_o by protein kinase A (PKA) + ATP, when the Cl^- concentrations bathing intracellular faces are low; and no effect of PKA + ATP on P_o with high cytoplasmicface Cl^- concentrations. These same properties were observed in Cl^- channels studied using excised patches of basolateral membranes from mouse MTAL cells. Moreover, in both bilayers and in excised patches, the sharpest fractional increase in Cl^- channel P_o occurred with cytosolic-face Cl^- concentration increases to values similar to the antidiuretic hormone (ADH)-dependent values of intracellular Cl^- activity in microperfused mouse MTAL segments, and these fractional P_o increases were adequate to account quantitatively for the ADH-dependent increase in basolateral membrane Cl^- conductance in microperfused mouse MTAL segments. Thus the excised-patch basolateral Cl^- channels reported here are reasonable candidates for those mediating net Cl^- absorption in the MTAL.