title: Renal basolateral membrane Na-Ca exchange is electrogenic.
abstract: A Na-Ca exchange system is present in highly purified basolateral renal tubular membranes. In the present study we examined the electrogenicity of the system by measuring 45Ca uptake in the presence of favorable electric gradient created by K and valinomycin, by measuring the uptake of the lipophilic cation methytriphenylphosphonium (MTPP+) and by utilizing the voltage-sensitive dye DiS-C3(5). In the presence of an inward directed K gradient, 45Ca uptake in basolateral vesicles loaded with Na and suspended in K was significantly higher in the presence than in the absence of valinomycin. Under conditions favoring the operation of Na-Ca exchange system (i.e. outward directed Na gradient and in presence of external calcium) MTPP+ uptake was significantly higher in the presence than in the absence of a Na. Na-dependent Ca uptake was associated with a decrease in the fluorescence of the voltage-sensitive dye DiS-C3(5), indicating hyperpolarization. Conversely, Na-dependent Ca extrusion was associated with an increase in the fluorescence of the dye indicating depolarization. The fluorescence changes seemed to be specific for Na and Ca since they could not be reproduced when Li replaced Na or when Mg replaced Ca. These data demonstrate that the Na-Ca exchange system in renal basolateral membranes is electrogenic with stoichiometry greater than 2:1 Na:Ca ratio.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D007684:Kidney Tubules / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D014634:Valinomycin; D012964:Sodium; D002118:Calcium