Modulation of cardiac gap junctions: The mode of action of arachidonic acid

Myocytes isolated from neonatal rat hearts were grown in culture dishes. Cell pairs were selected to examine the mode of action of arachidonic acid (AA) on gap junctions. The dual voltage-clamp method was used to measure intercellular currents and determine the gap junction conductance, g(j). Exposure of cell pairs to 10 mu M AA produced reversible uncoupling, Pretreatment with 10 mu M POCA (sodium-2-15-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate; which inhibits mitochondrial beta-oxidation) did not prevent AA-dependent uncoupling. Thus, it seems that metabolites of beta-oxidation are not involved in AA-induced impairment of g(j). Pre-exposure to 10 mu M indomethacin (which blocks the cyclooxygenase pathway of the AA-cascade) had no effect on AA-dependent uncoupling. This suggests that cyclooxygenase products such as prostaglandins or thromboxanes play no role in g(j) modulation. Exposure to 5 mu M NDGA (nordihydroguaiaretic acid; which inhibits the 5-lipoxygenase pathway) or 10 mu M ETYA (5,8,11,14-eicosatetrynoic acid; which inhibits the 12- and 15-lipoxygenase pathway) led to a reversible decrease in gi. Pre-treatment with 4-BPB (4-bromophenacyl bromide; which inhibits phospholipase A(2)) did not prevent the effects on g(j) by NDGA or ETYA. This renders it unlikely that g(j) is regulated by eicosanoids. Also, accumulation of endogenous AA cannot be responsible for NDGA- and ETYA-dependent uncoupling. Exposure to 75 mu M SKF-525A (inhibits the epoxygenase pathway) reversibly impaired g(j). This is consistent with a direct action of SKF-525(A) on g(j), but leaves open the possibility of an involvement of epoxides, The data gathered will be discussed in terms of molecular mechanisms. Due to their amphipathic character, AA, NDGA, ETYA and SKF-525A may interfere with g(j) by disturbing the lipid-protein interface of the cell membranes and thereby impair gap junction channels. (C) 1997 Academic Press Limited.