Modulation of Cardiac Gap Junctions: The Mode of Action of Arachidonic Acid

Abstract

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,gj. Exposure of cell pairs to 10μm AA produced reversible uncoupling. Pretreatment with 10μm POCA (sodium-2-[5-(4-chlorophenyl)-pentyl]- oxirane-2-carboxylate; which inhibits mitochondrialβ-oxidation) did not prevent AA-dependent uncoupling. Thus, it seems that metabolites ofβ-oxidation are not involved in AA-induced impairment ofgj. Pre-exposure to 10μm 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 ingjmodulation. Exposure to 5μm NDGA (nordihydroguaiaretic acid; which inhibits the 5-lipoxygenase pathway) or 10μm ETYA (5,8,11,14-eicosatetrynoic acid; which inhibits the 12- and 15-lipoxygenase pathway) led to a reversible decrease ingj. Pre-treatment with 4-BPB (4-bromophenacyl bromide; which inhibits phospholipase A2) did not prevent the effects ongjby NDGA or ETYA. This renders it unlikely thatgjis regulated by eicosanoids. Also, accumulation of endogenous AA cannot be responsible for NDGA- and ETYA-dependent uncoupling. Exposure to 75μm SKF-525A (inhibits the epoxygenase pathway) reversibly impairedgj. This is consistent with a direct action of SKF-525A ongj, 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 withgjby disturbing the lipid-protein interface of the cell membranes and thereby impair gap junction channels.