Direct stimulation by succinate of Na⁺:K⁺ pump in rabbit ciliary epithelium

Abstract

The effects of succinate on the intracellular potential difference, PD, were measured in isolated rabbit ciliary processes. Concentrationdependent increases in the hyperpolarization of PD occurred between 1 and 15 mM succinate in NaC1 Ringers. With 5 mM succinate, there was a 6 mV hyperpolarization. Even though the hyperpolarization of PD_I was comparable with 10 and 15 mM succinate, it was more sustained at the latter two concentrations. Succinate also elicited comparable hyperpolarizations of PD_I in either Cl^--free or HCO₃^- -free Ringers. Similarly, following incubation with either 0.1 mM DIDS or 3 mM BaCl₂ the effect of succinate on PD_I was unchanged. Five mM succinate had no effect if it was added after 5 mM malonate. Malonate (5 mM) rapidly reversed a 5 mM succinate-induced hyperpolarization of PD_I which also suggests a metabolically mediated effect on PD_I. An isosmotic substitution of Na⁺ with NMDG Ringers depolarized PD_I, whereas PD_I depolarized biphasically during exposure to 0.1 mM ouabain. The addition of 5 mM succinate had no effect on either the time course or the magnitude of the depolarization of PD_I during blocking of the Na⁺ :K⁺ pump with either Na⁺ -free Ringers or ouabain. Taken together, these results show that succinate selectively stimulates the Na⁺ :K⁺ pump, but has no effect on any Cl^-, HCO₃^- or a Ba²⁺-sensitive K⁺ conductance.