Chloride conductance of denervated gastrocnemius fibers from normal goats

Abstract

Membrane potentials, cable parameters, and component resting ionic conductances of gastrocnemius fibers from normal goats were measured in vitro at six to 32 days following denervation by section of the tibial nerve. Denervated fibers were depolarized an average of 11.6 +/- 1.5 mV (six preparations) from the control mean of 62.1 +/- 1.0 mV (124 fibers) over the period studied. Fibrillation, tetrodotoxin-resistant action potentials, and anode-break excitation were present in the denervated preparations after 13 days. The control cable parameters from 124 fibers (13 preparations) were membrane resistance, 1052 +/- 70 omega-cm2 and membrane capacitance, 6.2 muF/cm2. In denervated fibers membrane resistance increased two to three times in the 13 to 32 day period; membrane capacitance increased about 50% in normal solution at eight to nine, 27-28, and 32 days. Myoplasmic resistivity was assumed to be 112 omega-cm. Measurements were made at 38 degrees C. Component resting conductances were determined from the cable parameters in normal and chloride-free solution. Mean chloride conducantance GC1 and mean potassium conductance GK of control fibers were 776 +/- 49 mumhos/cm2 and 175 +/- 15 mumhos/cm2 (92 fibers), respectively. Following denervation GC1 increased slightly at six to nine days then fell to low values at 16 to 32 days that were close to or indistinguishable from zero. GK increased significantly to 372 +/- 40 mumhos/cm2 and 499 +/- 90 mumhos/cm2 at 16 to 20 and 32 days, respectively. It was concluded from these findings that GC1 and GK of mammalian skeletal muscle are controlled by factors from the nerve and/or muscle action potentials. Goat muscle is different from frog muscle in which GC1 does not change and GK decreases during denervation.