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 increasedT K. 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 (P A) are greater thanP Cl, at least during the substitution. The association ofP A>P Cl with an increase ofT K, upon exposure of the kidney to test-anions, is at best accounted for by a decrease ofP Cl. The pattern of voltage attenuation along the epithelial cable during anionic substitutions is also consistent with an increase ofT K via a decrease ofP Cl. 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:P acet,P lact,P pyruv,P prop,P form>P Cl≃P gluc,P glut. The test-anions propionate, lactate, pyruvate, acetate and formate tend to increaseT K, mainly by reducingP Cl. 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.
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Anagnostopoulos, T., Planelles, G. Organic anion permeation at the proximal tubule of Necturus. Pflugers Arch. 381, 231–239 (1979). https://doi.org/10.1007/BF00583254
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DOI: https://doi.org/10.1007/BF00583254