THE EFFECTS OF ESSENTIAL OIL OF MENTHA X VILLOSA ON SKELETAL-MUSCLE OF THE TOAD

The effects of the essential oil of Mentha x villosa (EOMV) was invest igated in saponin-permeabilized fibres and in intact sartorius muscle of the toad, in intact muscle EOMV at concentrations From 1 to 100 mu g/mL blocked the contraction induced by high (80 mM) potassium and ind uced potentiation of caffeine-induced muscle contraction, From 1 to 6 mg/mL EOMV elicited contraction in both depolarized (by 110 mM K+) and non-depolarized (4 mM K+) muscle fibres. This contraction was blocked by procaine, At 3 mg/mL EOMV depolarized the normal resting potential from -80.77 to -71.21 mV, but did not alter the transmembrane potenti al in the presence of 60 mM K+. EOMV (1 mg/mL) induced contraction of saponin-permeabilized muscle fibres with an intact sarcoplasmic reticu lum (SW), These data suggest that EOMV: (i) induces muscle contraction by releasing Ca2+ from SR; (ii) impairs the excitation-contraction co upling at a step before Ca2+ release from the SR. (C) 1997 John Wiley & Sons, Ltd.