Adaptive changes of H⁺ secreting cells in the epidermis of the leopard frog RANA PIPIENS

1. Mitochondria-rich (MR) cells in the integument of the southern leopard frog, Rana pipiens, berlandieri, were stained with AgNO₃ under a variety of environmental and metabolic treatment conditions known to increase H⁺ excretion rates across the skin. In this tissue AgNO₃ proved to be a good stain for discriminating the MR cell populations from the granular cells. 2. High salinity adapted southern frogs showed no change in the MR cell population. The inability of the MR cell number to significantly increase suggested that the increased H⁺ excretion rates previously seen in these animals were not due to increased MR cell proliferation. 3. The MR cell population was found to increase in the NaNO₃ adapted frogs, demonstrating the contribution of altered extracellular Cl^- concentrations on the regulation of MR cell density. 4. Animals that were placed in chronic metabolic acidosis or pre-treated with ibuprofen demonstrated an increased MR cell population. The current observations are consistent with previous findings that these treatment regimes increase H⁺ excretion, suggesting that one of the cellular adaptive mechanisms responsible for increasing H⁺ excretion involves increasing the MR cell density. 5. The results further suggest that prostaglandins may play a role in regulating H⁺ excretion in MR cells, and that either changes in intracellular pH or prostaglandin formation regulates cell proliferation.