Apical plasma membrane vesicles were isolated from cultures of immortalized thick ascending limb of Henle's loop (TALH) cells and sorbitol uptake was investigated using a rapid filtration technique. In the presence of Mg2+, Ca2+, ATP, and GTP sorbitol equilibrated within three minutes with the intravesicular space; this uptake was reduced by 75% when the incubation temperature was decreased from 37°C to 4°C. A lower level of uptake was also observed in the presence of 100 μm quinidine and when Ca2+ or ATP were omitted from the medium. Membranes preincubated with Mg2+, Ca2+, ATP, and GTP showed, however, a high sorbitol uptake in ATP-free medium. Staurosporine, but only at high concentrations of 200 nm, inhibited sorbitol uptake when present during the transport experiments or during the preincubation with ATP. Similar results were obtained with 1 μm trifluoperazine. Protein kinase C inhibitory peptide was ineffective whereas 20 nm KT 5926, at low concentrations a specific inhibitor of Ca2+/calmodulin-dependent kinase, attenuated the activation. On the basis of these data we suggest that a Ca2+/calmodulin-dependent kinase is a mediator of regulation of sorbitol plasma membrane permeability in renal medullary cells.
The Journal of Membrane Biology – Springer Journals
Published: Oct 1, 1997
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