Ionic Nature of the Outward-Going Rectification in Crab Skeletal Muscle Fibres

The outward-going rectification was examined in crab muscle fibres under current clamp and voltage clamp conditions. Experiments were performed on large diameter crab muscle fibres; these generate all-or-none responses. Under current clamp conditions, the outward-going rectification can be elicited in the muscle membrane in a choline chloride solution; it however disappears in CT free artificial sea water (ASW). Under voltage clamp conditions, in the absence of the inward Ca current (ASW plus Mn + + ions), step depolarizations produce an outward current with a single tail-current component, which is well separated from the initial capacity current. Shifts of the apparent reversal potential of the outward current produced by modifications in O or K concentration suggest that this current is not exclusively carried by Kions, but ď ions as well.