부산대학교 도서관

Isolated muscle bags from the parasitic nematode Ascaris suum were prepared by collagenase treatment and dissection. Single bags were mounted in a V‐shaped plastic pipette for voltage clamp application and intra‐ and extracellular perfusion. With ‘physiological’ intra‐ and extracellular solutions, depolarizing voltage steps from near the normal resting membrane potential, ‐40 mV, produced in leak‐corrected currents, a slowly activating outward current at potentials more positive than ‐20mV. At the end of the depolarizing pulse there was a slow inward tail current with a reversal potential near ‐20mV. Hyperpolarizing voltage steps produced an outward current relaxation and an outward tail current with the same reversal potential. The observations can be explained by the presence in the bag of a non‐selective cation channel current, Ibcat, that activates spontaneously at the holding potential; depolarization increases opening of the channel and hyperpolarization decreases opening. Bath‐applied acetylcholine in concentrations greater than 10(−7) M produced an increase in the amplitude of Ibcat. The effect of acetylcholine was not antagonized or prevented by 100 microM tubocurarine, suggesting the presence of a non‐nicotinic acetylcholine receptor. Atropine (100 microM) had no detectable influence on the effect of acetylcholine but the FMRFamide peptide, PF1, in concentrations > 1 microM, reduced the amplitude of Ibcat. Ibcat was maintained when Cs+ was used to replace intra‐ and extracellular cations, showing that the channels were permeable to Cs+. It is concluded that the bag membrane possesses a slow voltage‐activated non‐selective cation channel current, Ibcat. The effect of acetylcholine in the presence of nicotinic antagonist indicates the presence of non‐nicotinic acetylcholine receptors on the bag membrane. The effect of PF1 indicated the presence of PF1 receptors on the bag membrane.