Permeability changes associated with the action potential in procaine-treated crayfish abdominal muscle fibers.
Permeability changes associated with prolonged action potentials have been analyzed in procaine-treated crayfish abdominal muscle fibers. The effect of external Ca indicates that the increase in membrane conductance observed during the rising phase of the action potential is primarily due to a permeability increase for Ca. A remnant of the permeability increase may cause the succeeding plateau as shown by its high conductance and by the effect of low Mn. A delayed increase in conductance precedes the termination of the plateau phase. This is due to a delayed increase in permeability, probably for K, that is observed when depolarizing electrogenesis is eliminated. High external Ca reduces the action potential duration, the falling phase starting at a higher depolarization. These changes may be related to an earlier onset of the delayed increase in permeability, induced by a larger inside positivity in the presence of higher Ca. No "anomalous rectification" is seen in early or late I-V curves for small depolarizations. Ba may replace Ca in its role in depolarizing electrogenesis, and the first action potential induced in Ba saline has a large overshoot and a long duration. In higher Ba salines, action potentials are greatly prolonged. Long term soaking in Rb-containing or K-free saline also augments and prolongs the action potential. These changes are assumed to be related to depression of the K permeability of the membrane.
D000009:Abdominal Muscles; D000200:Action Potentials; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002463:Cell Membrane Permeability; D003445:Crustacea; D008345:Manganese / Q000494:pharmacology*; D009132:Muscles / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D011199:Potentiometry; D011343:Procaine / Q000494:pharmacology*; D012413:Rubidium / Q000494:pharmacology
D001464:Barium; D008345:Manganese; D011343:Procaine; D012413:Rubidium; D011188:Potassium; D002118:Calcium