Blockade by lobeline of potassium exchange in skeletal muscle

Summary

Lobeline (0.05 to 2.5 mM) caused depolarization of muscle fibers in frog sartorius muscle bathed in chloride-free solution. When the extent of depolarization was plotted against the log of the concentration of lobeline, the relationship was described by a straight line with a slope of 57 mV for a 10-fold change in the concentration of lobeline (0.2 to 2.0 mM). Like lobeline, butacaine (0.1 to 0.5 mM) caused muscle depolarization with a 57 mV change in membrane potential for a 10-fold change in the concentration of the local anesthetic. Lobeline (0.05 to 0.15 mM) depressed the depolarization of the muscle fibers caused by the elevation of (K⁺]₀ over a range of 2.5 to 50 mM. ⁴²K-exchange in resting muscle was also depressed by lobeline (0.05 to 0.25 mM). The blockade by lobeline of ⁴²K-efflux followed a typical dose-response relationship with 0.06 mM lobeline required to cause a 50% decrease of ⁴²K-efflux. These findings show that lobeline in concentrations not much greater than those required to block neuromuscular transmission, has a direct action on ion exchange in skeletal muscle. These actions on electrogenic mechanisms may contribute to the anti-nicotinic action of lobeline and to the desensitization of endplate acetylcholine receptors caused by lobeline.