Effect of channel blockers on potassium efflux from metabolically exhausted frog skeletal muscle

1. 86Rb and 42K have been used to assess potassium exchange in frog skeletal muscle which had been metabolically exhausted by electrical stimulation (1 Hz) after treatment with 2 mM-cyanide and 1 mM-iodoacetate. These conditions led to the development of rigor. 2. Poisoning by itself induced a small but variable increase in tracer efflux. Complete mechanical exhaustion subsequent to electrical stimulation was, however, accompanied by a 5-6 fold increase in the rate coefficient for both 86Rb and 42K efflux. In the case of rubidium this was maintained for at least 20 min and often for up to 1 h. 3. The increase in tracer efflux induced by metabolic exhaustion was inhibited by barium (0.03-5 mM) in a reversible and concentration-dependent manner. Inhibition was also observed with glibenclamide (3-100 microM), tolbutamide (0.3-2 mM), TEA (5-100 mM) and the local anaesthetics lignocaine (1-3 mM) and tetracaine (1 mM). Quinine produced a dual response consisting of an inhibitory component which was most clearly seen at low concentrations (0.3 mM) and an enhancement of tracer efflux that became increasingly dominant at higher concentrations (1-10 mM). 4. Both apamin (30 and 100 nM) and Israeli scorpion (Leiurus quinquestriatus) venom (16 micrograms ml-1) produced little or no block of the tracer efflux activated by metabolic exhaustion. Similarly 4-aminopyridine (3 mM) and decamethonium (0.3 mM) were without obvious effect. 5. It is concluded that metabolic exhaustion of frog skeletal muscle leads to an increased permeability to both 42K and 86Rb. Our results with channel blockers suggest that this K+ permeability can be attributed neither to the delayed rectifier nor to an apamin- or charybdotoxin-sensitive calcium-activated K+ permeability (PK(Ca) but may be predominantly due to activation of ATP-sensitive channels similar to those found in the beta-cells of pancreatic islets.