Effects of the anesthetics heptanol, halothane and isoflurane on gap junction conductance in crayfish septate axons: A calcium- and hydrogen-independent phenomenon potentiated by caffeine and theophylline, and inhibited by 4-aminopyridine

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Abstract
Summary This study has monitored junctional and nonjunctional resistance. [Ca2+] i and [H−] i , and the effects of various drugs in crayfish septate axons exposed to neutral anesthetics. The uncoupling efficiency of heptanol and halothane is significantly potentiated by caffeine and theophylline. The modest uncoupling effects of isoflurane, described here for the first time, are also enhanced by caffeine. Heptanol causes a decrease in [Ca2+] i and [H+] i both in the presence and absence of either caffeine or theophylline. A similar but transient effect on [Ca2+] i is observed with halothane. 4-Aminopyridine strongly inhibits the uncoupling effects of heptanol. The observed decrease in [Ca2−] i with heptanol and halothane and negative results obtained with different [Ca2+] o , Ca2+-channel blockers (nisoldipine and Cd2+) and ryanodine speak against a Ca2+ participation. Negative results obtained with 3-isobutyl-l-methylxanthine, forskolin, CPT-cAMP, 8Br-cGMP, adenosine, phorbol ester and H7, superfused in the presence and absence of caffeine and/or heptanol. indicate that neither the heptanol effects nor their potentiation by caffeine are mediated by cyclic nucleotides, adenosine receptors and kinase C. The data suggest a direct effect of anesthetics. possibly involving both polar and hydrophobic interactions with channel proteins. Xanthines and 4-aminopyridine may participate by influencing polar interactions. The potentiating effect of xanthines on cell-to-cell uncoupling by anesthetics may provide some clues on the nature of cardiac arrhythmias in patients treated with theophylline during halothane anesthesia.