Organic anion permeation at the proximal tubule of necturus: an electrophysiological study of the peritubular membrane.

Abstract

This study deals with the electrical responses of the peritubular membrane of the Necturus proximal tubule to 8 organic anions, in NaHCO3-free (trismaleate-buffered) and NaHCO3-containing solutions. The anions glutamate and gluconate brought about a small depolarization, but only in NaHCO3-free media. Benzene sulfonate did not alter significantly membrane p.d. The 5 other test-anions produced hyperpolarization. The magnitude of membrane depolarization elicited by high-K media was proportionally larger in the presence of the test-anions propionate, lactate, pyruvate, acetate and formate than with chloride: it is inferred that these anions increasedTK. The same 5 anions shifted in the negative direction the p.d. achieved at peak K-depolarization; according to a previous analysis (Anagnostopoulos, 1977), this observation suggests that their permeabilities (PA) are greater thanPCl, at least during the substitution. The association ofPA>PCl with an increase ofTK, upon exposure of the kidney to test-anions, is at best accounted for by a decrease ofPCl. The pattern of voltage attenuation along the epithelial cable during anionic substitutions is also consistent with an increase ofTK via a decrease ofPCl. In conclusion, the apparent sequence of relative anionic permeabilities, as obtained from the responses of the tissue to a single anion, irrespective of buffering procedures, is:Pacet,Plact,Ppyruv,Pprop,Pform>PCl≃Pgluc,Pglut. The test-anions propionate, lactate, pyruvate, acetate and formate tend to increaseTK, mainly by reducingPCl. The effect of glutamate and gluconate on physiologic ion permeabilities is too small to be specified with accuracy: it depends to some extent on the buffer used in the solutions.