Acid–base and electrolyte responses to low pH maintained by phosphate–citrate buffers in the bathing medium of the larval salamander Ambystoma tigrinum

Abstract

Larval Ambystoma tigrinum were exposed to an external pH of 3.5 to 7.5 using phosphate – citrate buffers in the bathing medium. Blood analysis of cannulated Ambystoma tigrinum at pH 5.5, 4.5, and 3.5 indicated their ability to maintain relatively stable arterial pH at the two higher values; however, at pH 3.5, the blood pH diminished over the 12-h period before death. The greater stability of arterial pH at higher external pH is partially due to a reversal of an initial increase in arterial [Formula: see text]. This may not be due entirely to pulmonary excretion of CO2 as it also occurred in animals that were forced to exchange gases solely across the skin – gill unit by being deprived of access to an air space. This result suggests increased skin – gill perfusion and (or) ventilation as a mechanism for lowering arterial [Formula: see text]. Sodium transport across the skin of A. tigrinum was measured over a buffered pH range of 3.5 to 7.5. Na+ influx decreased from 1.0 ± 0.1 μequiv. 10 g−1 h−1 (mean ± SEM) at pH 7.0 to 0.1 ± 0.1 μequiv. 10 g−1 h−1 at pH 3.5. Na+ efflux increased to 38.1 ± 8.7 μequiv. 10 g−1 h−1 from 4.1 ± 0.9 μequiv. 10 g−1 h−1 as pH declined from 7.0 to 3.5. Calcium added to the buffer at pH 4.5 decreased Na+ efflux at that pH. Na+ fluxes measured in nonbuffered, low-pH solutions revealed qualitatively similar patterns with lower efflux rates and lower critical pH values.