Effects of arachidonic acid on the gap junctions of neonatal rat heart cells.

Myocytes were isolated from neonatal rat hearts and grown in tissue-culture dishes for 1-2 days. Spontaneously formed cell pairs were used to study the conductance of gap junctions. The experiments involved a double voltage-clamp approach and whole-cell, tight-seal recording. Exposure to arachidonic acid (AA) produced a quasi dose-dependent decrease in junctional conductance, gi (binding constant, Kd = 4 microM; Hill coefficient, n = 0.75). AA-dependent uncoupling was reversible. Addition of 1 mg/ml albumin to the bath solution accelerated the recovery. During control, cell pairs exhibited a gradual decrease in gi (16.4% in 6 min). Exposure to 20 microM 4-bromophenacyl bromide, a phospholipase inhibitor, suppressed the decay in gi (1.8% in 6 min), suggesting that endogenous AA may be involved in spontaneous uncoupling. The effect of AA on gi was specific. Arachidic acid (100 microM) and arachidonamide (10 microM), structural analogues of AA, had no effect on gi. Currents recorded shortly before complete uncoupling caused by AA, or early during recovery from uncoupling, revealed random opening and closing of single channels. The single channel conductance, gamma i, was not affected by the concentration of AA (1 microM - 100 microM). The mean gamma i turned out to be 33.5 pS. The results suggest that AA-dependent uncoupling was caused via decrease in open channel probability, presumably mediated by a direct action on channel proteins.