Generation of action potentials in single nodes of Ranvier of isolated frog nerve fibers under the influence of nickel and cadmium ions
Tóm tắt
By experiments on single nodes of Ranvier of isolated nerve fibers of the frog we showed that in addition to a marked increase in the duration of repolarization after an action potential Ni and Cd ions also caused a rise in the critical level of membrane depolarization, an increased action potential level, an increase of amplitude of action potential, and a somewhat reduced steepness of its rising phase. Ni and Cd ions restored the ability to generate action potentials in nodes of Ranvier which had been modified by a 0.01% procaine solution, by an excess of potassium ions (30 mM/l KCl) or slightly injured mechanically during dissection. It was only when the Na concentration in the medium was reduced that the action potential could be restored. Ni and Cd ions greatly slowed and reduced the cathodic rise in the critical level and reduced the amplitude of action potentials. Cysteine (10−2–10−3 M) eliminated all the effects of the ions we have mentioned. We suggest that by binding the SH-groups of the proteins of the nerve fiber, nickel and cadmium reduce the rate of inactivation and the increase of potassium permeability during polarization, and, in addition, weaken the initial inactivation of the membrane (I-h), whenever this was brough about by modifying influences.
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