HeLa cells express cAMP-inhibitable sodium-dependent phosphate uptake.
Receptor-mediated regulation of the sodium-phosphate symporter, and hence sodium-dependent phosphate uptake, typically relates to epithelial cells of renal origin. In this study we have characterized sodium-dependent phosphate uptake and aspects of its receptor-mediated regulation in the HeLa cell line, a cell line derived from a human epithelioid carcinoma. Phosphate uptake (greater than 90% sodium dependent; Vmax = 4.02 +/- 0.24 nmol.mg and Km = 0.11 +/- 0.02 mM phosphate at 140 mM sodium) was kinetically similar to that observed in opossum kidney cells. Incubation with vasoactive intestinal peptide (VIP) resulted in a dose-dependent (50% maximal dose of 8.8 +/- 3.6 nM) approximately fivefold increase in basal adenosine 3',5'-cyclic monophosphate (cAMP) levels (basal = 14.6 +/- 1.7 pmol.mg protein-1.15 min-1; VIP stimulated = 72.7 +/- 13.2 pmol.mg protein-1.15 min-1), as well as a dose-dependent maximal 32.6 +/- 5.5% decrease in sodium-dependent phosphate uptake (50% maximal decrease of 46.2 +/- 21.2 nM). The VIP-induced decrease in phosphate uptake was due to decrease in maximal transport (VmaxVIP = 2.78 +/- 0.16 nmol.mg protein-1.3 min-1) and not to a change in the affinity of the transporter for phosphate (KmVIP = 0.11 +/- 0.01 mM phosphate). Preincubation of HeLa cells with forskolin and cholera toxin, which stimulate adenylate cyclase, resulted in dose-dependent decreases in sodium-dependent phosphate uptake. Incubation with 8-bromo-cAMP and dibutyryl cAMP, permeant analogues of cAMP, similarly resulted in a dose-dependent decrease in sodium-dependent phosphate uptake.(ABSTRACT TRUNCATED AT 250 WORDS)
Raymond, JR; Middleton, JP; Dennis, VW
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