Comparison has been made between innervated and chronically denervated frog sartorius muscle fibers for resting potentials and a number of features of the action potential. Muscles were obtained from force-fed frogs maintained at room temperature for periods up to one year, and were studied with intracellular microelectrodes. Denervated muscles increased in sensitivity to acetylcholine by 100-400-fold. Studies were made in normal Ringer's solution, and in media in which concentrations of K+, Na+, Ca++, and C1-were altered. The only significant differences noted between the denervated and the innervated fibers were a reduction in the maximum rate of fall of the action potential (ca. 20% ) and an increase in the fall time of the active membrane potential (ca. 25%). These differences were present in normal Ringer's solution and remained when the bathing medium was modified. The resting membrane potential of denervated and innervated muscles varied with log [Kc], in exactly the same manner, and followed the theoretical relation proposed by Hodgkin (Proc. Roy. SOC., B, 148: 1-37, '58), with the term representing the ratio of the sodium to potassium permeabilities assigned a value of 0.01. The results suggest that ( a ) the resting sodium and potassium permeabilities are reduced proportionately after denervation, since it is known that denervated frog muscle has a smaller potassium permeability, and (b) the mechanism controlling the increase in potassium conductance during the action potential is less available after denervation. Data indicate that the system controlling the sodium permeability is capable of activation to the same extent as in innervated muscles. Muscles which had been allowed to reinnervate did not show the differences presented by the denervated muscles. Innervated and denervated muscles did not show any signscant changes in maximum rates of rise or fall of the action potential, nor of the active membrane potential amplitude over a 30 mV range of resting membrane potentials, indicating that the sodium and potassium permeability systems are fully available in frog muscle at membrane potentials larger than -80mV.It was previously reported that neither the resting potential (RP) nor several attributes of the action potential (AP) of frog sartorius muscle was altered by chronic denervation (Levine, '61). This conclusion was based on the finding that no significant mean difference existed for any of the parameters studied, between "denervated-innervated" pairs of muscles from the same frogs. However, when a comparison was run between the overall means of muscles from operated animals and corresponding overall means from a comparable group of unoperated animals, the maximum rate of rise (MRR) and the maximum rate of fall (MRF) of the action potential were significantly slower in both muscles from the operated frogs. These findings thus raise two questions: what factor( s), non-specific to chronic denervation, affected both muscles of the operated animals? (2) did operation of the factors( s) mask d...
