Ionic Composition of Haemolymph and Myoplasm in Lepidoptera in Relation to Their Membrane Potentials

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Abstract
1. The results of haemolymph and myoplasm ionic analysis show that lepidopteran muscle has a low transmembrane potassium gradient, and a sodium gradient such that Na0/Nai is less than unity 2. The theoretical potassium electrode potential is much smaller than the observed resting potential, and the sodium electrode potential is totally unrelated to the observed « undershoot » in lepidopteran muscle. The chloride electrode potential gives a much closer fit to the resting potential, but the transmembrane potassium and chloride gradients are not reciprocal. 3. The possible existence of a peripheral diffusion barrier is discussed and rejected. On the evidence available, it seems likely that active transport of ions is responsible, at least in part, for membrane potential maintenance in the Lepidoptera, and possibly in some other insects.