Electrical properties of obliquely striated muscle fibre membrane ofAnodonta glochidium

Abstract

(1) Electrical properties of the obliquely striated fibers of the adductor muscle of glochidium larvae ofAnodonta implicata were studied by means of intracellular recording and polarization techniques. (2) The muscle fiber lacks transverse tubules and a large fraction (60–85%) of the surface membrane is involved in dyadic junctions with cisternae of the sarcoplasmic reticulum. (3) The resting potential and the overshoot of the action potential in the normal saline are −42.4±6.6 mV and 3.8±4.2 mV, respectively. (4) The overshoot is not altered by the total removal of external Na or by the addition of the 3 μM tetrodotoxin. (5) The overshoot is decreased by reducing the external Ca, and the action potential is eliminated by 1 mM LaCl3 in normal saline. (6) The action potential is produced by an increase in Ca permeability. (7) The specific membrane resistance and capacitance are 9.8±3.6 kΩ·cm2 and 2.1±0.4 μF/cm2, respectively. (8) The fiber membrane shows a marked delayed rectification but no significant inward-going or anomalous rectification. (9) After the suppression of action potentials by La, electronmicroscopy reveals an accumulation of La on the surface membrane including at the dyadic junctions.