Hormone-responsive Ca2+ entry in distal convoluted tubules.

This editorial review focuses on recent observations regarding the mechanism and regulation of calcium transport in hormone-sensitive distal convoluted tubules. Parathyroid hormone (PTH) and calcitonin increase active calcium absorption by distal convoluted tubules. Occupancy of these peptide hormone receptors results in the activation of both protein kinase A and protein kinase C. The inhibition of either kinase blocks calcium transport. The time course of stimulation of calcium entry in distal convoluted tubules by PTH is slow compared with that by calcitonin. The latency associated with PTH action may be due to the induction of protein synthesis. PTH and calcitonin hyperpolarize membrane voltage, which in turn increases calcium entry. Calcium entry is mediated by calcium channels. These channels exhibit a low, single-channel conductance and are sensitive to dihydropyridine-type calcium channel blockers. Unlike L-type calcium channels, the channel open probability of distal convoluted tubule calcium entry channels is increased upon hyperpolarization. This novel combination of properties suggests that the underlying structure of these calcium entry channels may be unique.