CA-MEDIATED AND INDEPENDENT EFFECTS OF ARACHIDONIC-ACID ON GAP-JUNCTIONS AND CA-INDEPENDENT EFFECTS OF OLEIC-ACID AND HALOTHANE

In Novikoff hepatoma cell pairs studied by double perforated patch cla mp (DPPC), brief (20 s) exposure to 20 mu M arachidonic acid (AA) indu ced a rapid and reversible uncoupling. In pairs studied by double whol e-cell clamp (DWCC), uncoupling was completely prevented by effective buffering of Ca-i(2+) with BAPTA. Similarly, AA (20 s) had no effect o n coupling in cells perfused with solutions containing no added Ca2+ ( SES-no-Ca) and studied by DPPC, suggesting that Ca2+ influx plays an i mportant role. Parallel experiments monitoring [Ca2+](i) with fura-2 s howed that [Ca2+](i) increases with AA to 0.7-1.5 mu M in normal [Ca2](0), and to similar to 400 nM in SES-no-Ca solutions. The rate of [Ca 2+](i) increase matched that of G(j) decrease, but [Ca(2+)](i) recover y was faster. In cells studied by DWCC with 2 mM BAPTA in the pipette solution and superfused with SES-no-Ca, long exposure (1 min) to 20 mu M AA caused a slow and virtually irreversible uncoupling. This result suggests that AA has a dual mechanism of uncoupling: one dominant, fa st, reversible, and Ca2+-dependent, the other slow, poorly reversible, and Ca2+-independent. In contrast, uncoupling by oleic acid (OA) or h alothane was insensitive to internal buffering with BAPTA, suggesting a Ca2+-independent mechanism only.