Abstract
Rb + influx was used to assess NaKCl cotransport and Na,K-ATPase activities in cultured monkey retinal pigment epithelium. Bumetanide-sensitive (NaKCl cotransport-mediated) Rb + influx exceeds ouabain-sensitive (Na,K-ATPase-mediated) Rb + influx, with these two transporters accounting for ∼ 95% of total Rb + uptake. Half-maximal inhibition of Rb + influx by bumetanide is attained at 75 n m bumetanide. The bumetanide-sensitive Rb + influx depends on both extracellular Na + and Cl −, and is activated by extracellular Rb + with a relatively high affinity. NaKCl cotransport activity is stimulated (2·5-fold) by increased extracellular osmolarity. Elevated cAMP content and glycolytic inhibition both depress cotransport activity. Cyanide application, however, had very little effect on NaKCl cotransport activity. Monkey retinal pigment epithelial cells, maintained in culture, provide a system in which the activity and regulation of cation transport mechanisms can be examined.
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