Parathyroid hormone receptors in control of proximal tubule function

Parathyroid hormone action on renal proximal tubule function involves phospholipase C/protein kinase C as well as adenylate cyclase/protein kinase A mediated regulatory pathways. Tissue culture experiments suggest that low concentrations of PTH affect preferentially the phospholipase C/protein kinase C pathway. In vivo, both regulatory cascades are probably involved in the regulation of proximal tubule function. It is not clear at present whether the two intracellular pathways are linked to one or two PTH receptors. A polarized distribution of PTH receptor(s) involving different second messengers appears possible in proximal tubule epithelial cells. High-affinity (Kd 10(-11)-10(-12) M) PTH receptors in the range of circulating PTH concentrations in vivo remain to be identified. Structural and functional characterization of PTH receptors as well as of the PTH-sensitive intracellular mediators and transport systems form the basis for a better understanding of PTH-dependent regulation of proximal tubule function.