Components of resting membrane electrogenesis in Lepidopteran skeletal muscle

Abstract

The partial contributions of K +, Na +, Cl −, Mg 2+ and an electrogenic, metabolic pump to resting membrane electrogenesis in skeletal muscles of Chilo partellus (Lepidoptera) have been quantified. The contributions of the ions were evaluated by ionic substitution experiments, whilst the role of the pump was investigated by cooling and application of ouabain. In response to changes in extracellular K +, Na + and Cl − activities, membrane potentials changed in rapid, graded, sustained and reversible steps. For a 10-fold change in the extracellular activity, the maximal changes in the membrane potentials were 31 mV (K +), 2 mV (Na +) and 17 mV (Cl −). In constrast, changing the extracellular Mg 2+ concentration had no immediate effect on resting potentials. Cooling preparations by 14°C from room temperature resulted in rapid membrane depolarizations of some 12 mV. However, application of 1 mM ouabain in Ringers containing varying concentrations of K + had no effect on the membrane potential. It followed, therefore, that a metabolic mechanism was also involved in electrogenesis, but this was unlikely to be an ouabain-sensitive (Na +K +) ATPase. The contributions of K +, Na +, Cl − and the metabolic pump were sufficient to account quantitatively for the prevailing resting membrane potential (mean, −46 mV) with an error margin of some 7%.