Mobility of voltage-dependent ion channels and lectin receptors in the sarcolemma of frog skeletal muscle.

Abstract

ABSTRACT The mobility of lectin receptors and of two types of ion channels was studied in skeletal muscles of the frog Rana temporaria. Lectin receptors were labeled with fluorescent derivatives of succinyl-concanavalin A (Con A) or wheat germ agglutinin (WGA), and their mobility was measured by fluorescence recovery after photobleaching. Of the receptors for WGA,-53 % were free to diffuse in the plane of the membrane, with an average diffusion coefficient as found in other preparations (D = 6.4 X 10- " cm'/s). Con A receptors were not measurably mobile. The mobility of voltage-dependent Na and K (delayed rectifier) channels was investigated with the loose-patch clamp method, coupled with through-the-pipette photodestruction of channels by ultraviolet (UV) light. Na channels were not measurably mobile (D < _ 10-'2 cm'/s). With K channels, photodestruction was followed by a small but consistent recovery of K current, which suggested that some K channels diffused in the plane of the membrane. Our results with K currents are best ft if 25 % of the K channels diffuse with D = 5 X 10-11 cm2 /s, with the remainder bein