MEMBRANE CURRENTS IN A CALCIUM TYPE MUSCLE MEMBRANE UNDER VOLTAGE CLAMP

  • 1 January 1978
    • journal article
    • research article
    • Vol. 27  (5) , 457-466
Abstract
Ionic current components (4) were identified in the total membrane current recorded under voltage clamp conditions from the muscle membrane of the crayfish (Astacus fluviatilis). The early inward current component is dependent on the presence of Ca2+ ions, disappears in Ca2+ free solutions and is insensitive to variation of external Na+ ion variations and tetrodotoxin. The outward current consists of at least 3 components; an early, late and slow outward current. The outward currents are sensitive to TEA [tetraethylammonium] and their reversal potentials differ. The early K current may be separated in a proportion of fibers by a hump from the late K current. Insufficient space clamp as a cause of the hump was excluded by comparing the size of the clamped membrane area with the distribution of large membrane clefts in the fiber. The early outward current is critically dependent on the presence of Ca2+ ions. It is relatively more sensitive to TEA ions and to conditioning depolarization than the late outward current.