AJP - Cell Physiology, Vol 248, C217-C227, Copyright © 1985 by the American Physiological Society

Potassium movements in denervated frog sartorius muscle

¹ Cátedra de Fisiología con Biofísica, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, 1900, Argentina; and Instituto de Investigaciones Médicas, Universidad Nacional de Buenos Aires, Buenos Aires 1427, Argentina

The movement of ⁴²K⁺ across the sarcolemma and the resting membrane potential (V_M) 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. 1) In the absence of any driving force on K⁺, i.e., when the difference between V_M and the K⁺ equilibrium potential (E_K) is zero (V_M – E_K = 0), the K⁺ conductance (g_K) was 368 µS·cm^–2 in control and 282 µS·cm^–2 in denervated muscle. 2) The reduced g_K of denervated muscles results from the addition of the opposite changes in the conductances of a Rb⁺-sensitive inward rectifying pathway (g_IR), which decreases, and a Rb⁺-insensitive linear channel (g_L), which increases. Thus in control muscles g_K (368 µS·cm^–2) equals g_IR (359 µS·cm^–2) plus g_L (9 µS·cm^–2), while in denervated muscles g_K (282 µS·cm^–2) equals g_IR (198 µS·cm^–2) plus g_L (84 µS·cm^–2). 3) Denervation significantly reduces the inward rectifying properties of the resting K⁺ permeability system. In the presence of outward driving forces on K⁺ (V_M – E_K > 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. 4) No changes were observed during the first 2 wk after denervation.

Submitted on July 25, 1983
Accepted on July 11, 1984