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Original Article

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

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Pages 787-792 | Received 24 Apr 1990, Accepted 13 Jul 1990, Published online: 02 Jul 2009
 

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 PDI was comparable with 10 and 15 mM succinate, it was more sustained at the latter two concentrations. Succinate also elicited comparable hyperpolarizations of PDI 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 PDI 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 PDI which also suggests a metabolically mediated effect on PDI. An isosmotic substitution of Na+ with NMDG Ringers depolarized PDI, whereas PDI 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 PDI 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.

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