ANALYSIS OF SUBSYNAPTIC SITE OF ACTION OF THEOPHYLLINE ON ISOLATED CAT TENUISSIMUS MUSCLE

  • 1 January 1976
    • journal article
    • research article
    • Vol. 197  (3) , 647-652
Abstract
The subsynaptic actions of theophylline were studied by employing intracellular recording techniques in the isolated cat tenuissimus muscle. Theophylline produced a dose-dependent increase in miniature end-plate potential (MEPP) amplitude. The maximal increase (30%) in MEPP amplitude occurred at the 1.8 mM concentration of theophylline with a concomitant depolarization of the resting membrane potential. Depolarizations induced by acetylcholine were potentiated by 1.8 mM theophylline. This effect was less evident with a carbachol-induced depolarization, which indicates a possible anticholinesterase action. Input resistance decreased significantly; this effect correlated with the decline in resting membrane potential produced by theophylline. The equilibrium potential of the EPP [end-plate potential] was shifted to a more positive value in a reversible manner. The conductance change due to MEPPs, acetylcholine and carbachol was increased by theophylline treatment. The shift in equilibrium potential of the EPP coupled with a slight anticholinesterase action may account for the increase in MEPP amplitude observed with theophylline treatment.