Activation of Na⁺-Independent Mg²⁺ Efflux by 20-Hydroxyeicosatetraenoic Acid in Rat Renal Epithelial Cells

Abstract

Renal epithelial cells may have Mg²⁺ transport pathways that regulate intracellular free Mg²⁺ concentration ([Mg²⁺]_i) and reabsorption into the body. In mag-fura 2 fluorescent measurement, extracellular Mg²⁺ removal induced a Na⁺-independent [Mg²⁺]_i decrease. The [Mg²⁺]_i decrease was suppressed by methyl arachidonyl fluorophosphonate, a cytosolic and Ca²⁺-independent phospholipase A₂ (iPLA₂) inhibitor, and bromoenol lactone, an iPLA₂ inhibitor, but it was not suppressed by a secretory phospholipase A₂ inhibitor. On the contrary, the [Mg²⁺]_i decrease was enhanced by the addition of exogenous arachidonic acid (AA). Next, we examined the effect of AA metabolite inhibitors on the [Mg²⁺]_i decrease. 17-octadecynoic acid inhibited the [Mg²⁺]_i decrease, but indomethacin and nordihydroguaiaretic acid did not. In the 17-octadecynoic acid-treated cells, 20-hydroxy-(5Z,8Z,11Z,14Z)-eicosatetraenoic acid (20-HETE) recovered the [Mg²⁺]_i decrease. Nicardipine inhibited both the basal and the 20-HETE-enhanced [Mg²⁺]_i decrease. These results suggest that 20-HETE is a key mediator in the activation of Na⁺-independent Mg²⁺ efflux.