CL- CHANNELS IN BASOLATERAL RENAL MEDULLARY VESICLES .9. 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 cytoplasmic-face 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.