Control of phosphate transport in flounder renal proximal tubule primary cultures

Unidirectional mucosal-to-serosal (Jm----s) and serosal-to-mucosal (Js----m) transepithelial phosphate fluxes across monolayers of flounder (Pseudopleuronectes americanus) renal proximal tubule cells in primary culture were examined for effects of diacylglycerols, phorbol ester, A23187, forskolin, and extracellular phosphate availability. Tissues were cultured on floating collagen rafts and studied short circuited in Ussing chambers. Transepithelial electrical properties were continuously monitored and were unaffected by any of the treatments compared with paired controls. Under usual conditions (phosphate = 0.4 mM) tissues invariably displayed net phosphate reabsorption [Js----m = 2.3 +/- 0.52; Jm----a = 7.1 +/- 1.77; Jnet = 4.9 +/- 1.45 (SE) nmol.cm-2.h-1]. Acute elevation of bath phosphate concentration above 0.5 mM stimulated net secretion. Exposure to 100 microM 1,2-dihexanoyl-sn-glycerol stimulated net phosphate secretion within 30 min, the result of a fivefold increase in Js----m. Phorbol-12,13-didecanoate stimulated net phosphate secretion by increasing Js----m and decreasing Jm----s. The inactive diacylglycerol, 1,3-didecanoyl-rac-glycerol (100 microM), had no effect on phosphate fluxes. A23187 stimulated net phosphate secretion; Jm----s was reduced almost fourfold while Js----m was increased threefold. Forskolin (10 microM) stimulated net reabsorption more than threefold after a long latency (2 h). These data indicate that renal phosphate secretion and reabsorption may be regulated by several putative intracellular messengers. In addition, extracellular phosphate availability may modulate renal phosphate handling.