Role of sodium on H⁺ excretion in the integument of the leopard frog Rana pipiens

1. 1. The northern leopard frog, Rana pipiens, pipiens, in contrast to the southern leopard frog, Rana pipiens, berlandieri, did not demonstrate any significant H⁺ excretion across its integument even during a challenge of chronic metabolic acidosis. Likewise, no increase in the number of H⁺ secreting mitochondria-rich cells were observed in the northern frogs. 2. 2. Under normal acid-base conditions in the southern frogs, H⁺ excretion was found to be dependent on mucosal sodium concentrations, whereas during chronic metabolic acidosis, H⁺ excretion was independent of mucosal sodium concentrations, but was amiloride sensitive. 3. 3. High salinity adapted southern frogs, under normal and acidotic conditions, had enhanced H4⁺ excretion rates as compared to the control non-salt adapted frogs. 4. 4. Blood analyses demonstrated that significant acid-base changes were the result of systemic acidosis and not due to salt adaptations. Blood Na⁺ and K⁺ concentrations were also efficiently maintained during salt adaptations or chronic metabolic acidosis. 5. 5. The results suggest that H⁺ excretion in epithelia can be influenced by the sodium transport state of the cell and the systemic acid-base profile. Models are proposed explaining these relationships.