Section-specific H+ flux in renal tubules of fasted and fed goldfish [RESEARCH ARTICLE]

Sandra Fehsenfeld, Dennis Kolosov, Chris M. Wood, and Michael J. O'Donnell A recent study demonstrated that in response to a feeding-induced metabolic acidosis, goldfish (Carassius auratus) adjust epithelial protein and/or mRNA expression in their kidney tubules for multiple transporters known to be relevant for acid–base regulation. These include Na+/H+ exchanger (NHE), V-type H+-ATPase (V-ATPase), cytoplasmic carbonic anhydrase, HCO3– transporters and Rhesus proteins. Consequently, renal acid output in the form of protons and NH4+ increases. However, little is known about the mechanistic details of renal acid–base regulation in C. auratus and teleost fishes in general. The present study applied the scanning ion-selective electrode technique (SIET) to measure proton flux in proximal, distal and connecting tubules of goldfish. We detected increased H+ efflux into the extracellular fluid from the tubule in fed animals, resulting from paracellular back-flux of H+ through the tight junction. By applying inhibitors for selected acid–base regulatory epithelial transporters, we found that cytosolic carbonic anhydrase and HCO3– transporters were important in mediating H+ flux in all three tubule segments of fed goldfish. Contrastingly, V-ATPase seemed to play a role in H+ flux only in proximal and distal tubules, and NHE in proximal and connecting tubules. We developed working models for transport of acid–base relevant equivalents (H+, HCO3&ndash...
Source: Journal of Experimental Biology - Category: Biology Authors: Tags: RESEARCH ARTICLE Source Type: research