Alpha 2-adrenergic receptors activate phospholipase C in renal epithelial cells

The effects of alpha 2-adrenergic receptors are usually attributed to inhibition of adenylyl cyclase through pertussis toxin-sensitive Gi coupling. In kidney distal convoluted tubule (DCT) cells, stimulation of Na+/K(+)-ATPase by alpha 2 receptors involves activation of protein kinase C (PKC). To identify the signal pathways coupled to alpha 2 receptors, we measured cAMP production and show that the alpha 2 agonist B-HT 933 had no effect on basal or stimulated (forskolin, parathyroid hormone) cAMP accumulation in DCT cells but inhibited parathyroid hormone-stimulated cAMP accumulation in proximal tubule cells. I tested whether alpha 2 receptors on DCT cells stimulate PKC through second messengers generated from phospholipase C (PLC) activation. In DCT cells, B-HT 933 increased inositol-1,4,5-trisphosphate formation by 4-6-fold over control and increased diacylglycerol formation by 46%. Basal intracellular calcium concentration in single DCT cells averaged 114 nM and increased within 2 min to 196 nM with B-HT 933. Treatment with the PLC inhibitor U-73122 but not pertussis toxin blocked B-HT 933-induced rises in inositol-1,4,5-trisphosphate and intracellular calcium concentration. B-HT 933 increased PKC activity by 45% over control in DCT cells. These findings provide evidence that alpha 2-adrenergic receptors activate PLC in DCT cells through a pertussis toxin-insensitive mechanism.