Coexpression and stimulation of parathyroid hormone receptor positively regulates slowly activating IsK channels expressed in Xenopus oocytes.

Expression of the IsK protein in Xenopus oocytes induced the characteristically slow, voltage-dependent outward currents. Superfusion with the parathyroid hormone (PTH) peptide 1-34 had no effect on IsK when expressed alone, but increased IsK when IsK was coexpressed with the PTH-receptor. PTH receptor stimulation caused a shift of IsK conductance-voltage relationship to more negative potentials, and a decrease of both the rate of IsK activation and deactivation. IsK regulation by PTH was independent of extracellular Ca2+, and was also present IsK protein mutants lacking the protein kinase C consensus site. However, regulation of IsK by PTH was mimicked by activators of protein kinase A (PKA) and greatly reduced in the presence of the kinase inhibitors staurosporine and H89. These results suggest that PTH regulates IsK by a mechanism involving phosphorylation independent of protein kinase C (PKC). Such regulation may play a role in proximal tubule cells of the kidney, where both PTH receptor and the IsK protein are expressed.