ION-CHANNEL ACTIVITY IN LOBSTER SKELETAL-MUSCLE MEMBRANE

Ion channel activity in the sarcolemmal membrane of muscle fibers is c ritical for regulating the excitability, and therefore the contractili ty, of muscle. To begin the characterization of the biophysical proper ties of the sarcolemmal membrane of lobster exoskeletal muscle fibers, recordings were made from excised patches of membrane from enzymatica lly induced muscle fiber blebs. Blebs formed as evaginations of the mu scle sarcolemmal membrane and were sufficiently free of extracellular debris to allow the formation of gigaohm seals. Under simple experimen tal conditions using bi-ionic symmetrical recording solutions and main tained holding potentials, a variety of single channel types with cond uctances in the range 32-380 pS were detected. Two of these ion channe l species are described in detail, both are cation channels selective for potassium. They can be distinguished from each other on the basis of their single-channel conductance and gating properties. The results suggest that current flows through a large number of ion channels tha t open spontaneously in bleb membranes in the absence of exogenous met abolites or hormones.