Calcium participation in ATP and arachidonic acid but not in oleic acid and halothane induced gating of gap junctions in Novikoff cells

Abstract

1. ABSTRACT The effects of ATP and arachidonic acid on junctional conductance (G j ) were studied in Novikoff hepatoma cells, while monitoring either [Ca 2+ ] i , with fura-2, or both membrane and junctional currents, with double whole-cell (DWCC) or double perforated patch clamp (DPPC). ATP (100 μM) increased [Ca 2+ ] i to 400-1200 nM and in most cells decreased G j by 30-40%. Simultaneously, an outward current developed, with a reversal potential of −80 mV at normal [K + ] o that became 0 at 140 mM [K + ] o , indicating that it is a Ca 2+ -activated K-current. Current peaks coincided with G j minima, indicating that both phenomena result from an increase in [Ca 2+ ] i . Arachidonic acid (AA, 20 μM, 20 s) had similar effects on [Ca 2+ ] i and G j . Internal BAPTA prevented G j changes, suggesting Ca 2+ dependence, but long exposures (20 μM AA, 1 min) caused uncoupling even with internal BAPTA, indicating that AA has both a Ca 2+ mediated and a Ca 2+ independent effect on coupling. However, Ca 2+ dependent uncoupling had a much faster time course. BAPTA did not prevent uncoupling by oleic acid (OA) or halothane, suggesting that they act in Ca 2+ independent way.