The dissociation between renal HCO3- reabsorption and H+ secretion in the skate, Raja erinacea.

Abstract

The rate of H+ secretion from cell to lumen was studied in the proximal nephron segment of the skate,Raja erinacea. The split drop technique was used, and the rate of acidification (from pH 7.5 to 5.8) was estimated by the time of the color change of the buffer dye, bromcresol purple (pK 6.2). The secretory cells (in each liter of their volume) produced 40·10−6 mol H+/min; calculated for the whole fish the rate of H+ excretion is about 0.15·10−6 mol/min. This rate is about the same as observed in vivo in the free swimming elasmobranch; and about 1/5 to 1/10 that calculated for the production of H+ from the uncatalyzed hydration of CO2, since elasmobranchs have no renal carbonic anhydrase. Addition of large amounts of NaHCO3 (17 fold) to the bromcresol purple did not change the time requested for the color change of this buffer dye; addition of phosphate prolonged the time significantly. It is concluded that luminal HCO3− in this species is very rapidly reabsorbed by a process not involving proton production by tubular cells.