AJP - Cell Physiology, Vol 248, Issue 3 219-C227, Copyright © 1985 by American Physiological Society
Potassium movements in denervated frog sartorius muscle
R. A. Venosa and B. A. Kotsias
The movement of 42K+ across the sarcolemma and the resting membrane
potential (VM) of normal and denervated frog sartorius muscle were studied
under several experimental conditions in preparations initially
equilibrated in 100 mM K+ and 219 mM Cl-. The results can be summarized as
follows. In the absence of any driving force on K+, i.e., when the
difference between VM and the K+ equilibrium potential (EK) is zero (VM -
EK = 0), the K+ conductance (gK) was 368 microseconds . cm-2 in control and
282 microseconds. in denervated muscle. The reduced gK of denervated
muscles results from the addition of the opposite changes in the
conductances of a Rb+-sensitive inward rectifying pathway (gIR), which
decreases, and a Rb+-insensitive linear channel (gL), which increases. Thus
in control muscles gK (368 microseconds . cm-2) equals gIR (359
microseconds . cm-2) plus gL (9 microseconds . cm-2), while in denervated
muscles gK (282 microseconds . cm-2) equals gIR (198 microsecond . cm-2)
plus gL (84 microseconds . cm-2). Denervation significantly reduces the
inward rectifying properties of the resting K+ permeability system. In the
presence of outward driving forces on K+ (VM - EK greater than 0) of 35-50
mV, the Rb+-sensitive inward rectifier channel appears to close completely
in both control and denervated muscles. In the latter, however, the effect
was not as well maintained as in the former, suggesting that its closing
mechanism might be altered by denervation. No changes were observed during
the first 2 wk after denervation.
