PGE₂ inhibits basolateral 50 pS potassium channels in the thick ascending limb of the rat kidney

To study the inhibition of the inwardly rectifying basolateral 50 pS potassium channels by PGE₂ we performed patch-clamp studies on the basolateral membrane of the rat kidney thick ascending limb. PGE₂'s effect was mimicked by the selective EP1- and EP3-receptor agonist, sulprostone, but was prevented by inhibiting protein kinase-C with calphostin-C. The mitogen-activated protein kinase inhibitor PD98059 (ERK) or SB203580 (p38) increased basal channel activity; however, while neither alone prevented the inhibitory effect of PGE₂, but using both of them together completely abolished PGE₂'s effect on channel activity. Treatment with PGE ₂ stimulated phosphorylation of both p38 and ERK in primary cultures of medullary thick ascending limb cells. The PGE₂-mediated mitogen-activated protein kinase activation was not affected by indomethacin, but was completely blocked by calphostin-C. These studies show that inhibition of basolateral 50 pS potassium channels by PGE₂ is mediated by protein kinase-C, which in turn stimulates mitogen-activated protein kinases in the thick ascending limb of the rat kidney.