Elevated extracellular K+ enhances arachidonic acid release in MDCK-D1 cells

Depolarization can alter the expression of membrane receptors and change certain receptor-mediated events, but previous studies have not assessed the impact of depolarization on generation of arachidonic acid and its metabolites (AA) in nonexcitable tissues. We assessed AA generation in Madin-Darby canine kidney (MDCK) cells grown for 3 days in increased extracellular [K+], which is known to acutely depolarize these cells. Growth under these conditions resulted in decreases in the number of alpha 1-adrenergic receptors (alpha 1 AR), a small decrease in receptor-mediated phosphoinositide hydrolysis, but increases in alpha 1 AR-mediated prostaglandin E2 formation and AA release. Calcium ionophore (A23187)-, melittin-, and bradykinin-stimulated AA release were also enhanced. The reduction in alpha 1 AR number and increased AA release were substantially reduced or eliminated when K(+)-treated cells were grown in the absence of extracellular calcium. The results provide evidence that hormone-stimulated AA release and prostaglandin production can be enhanced by chronic exposure to elevated extracellular K+ concentration, perhaps as a consequence of a depolarization-induced enhancement in phospholipase A2 activity. The results provide evidence for the parallel and independent regulation of the pathways for receptor-mediated phosphoinositide hydrolysis (phospholipase C activation) and AA release (phospholipase A2 activation) in MDCK cells.