Electrogenic Na-K pump in denervated mouse soleus muscles: Prolonged activation by briefly applied acetylcholine

Abstract

Thin preparations of mouse soleus muscles denervated for 3–11 days were bathed in Cl-free solutions. The membrane potential (microelectrode technique) was an average of −65.6 mV. On application of 10 μM acetylcholine (ACh) the membrane potential fell to −2 to −8 mV. Following the washout of ACh it returned to values 9–24 mV more negative than before ACh. The membrane potential gradually returned toward the initial level during the ensuing 40–60 min. No hyperpolarization occurred when Na ions were absent during the application and washout of ACh or in the presence of 0.1 mM ouabain. The hyperpolarization was enhanced by replacing the Na ions by Li or Tris ions following an application of ACh in the presence of Na +. The hyperpolarization was suppressed by ouabain irrespective of whether the drug was applied in the presence or absence of Na +. The membrane potential was diminished by reducing [K +] from 4 to 1 mM in the absence of Na + before ACh, but it was increased by the same procedure by up to 20 mV following the application of ACh. This indicates that the hyperpolarization was not entirely due to a K-depleting action of the Na-K pump at the membrane surface.