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Journal of Experimental Biology 78,29-45 (1979)
Published by Company of Biologists 1979

Electrogenic Na⁺ Transport in a Crustacean Coxal Receptor

MAURIZIO MIROLLI ¹

¹ Medical Sciences Program, Indiana University, Bloomington, Indiana 47401, and Laboratory of Sensory Sciences, University of Hawaii, Honolulu, Hawaii 96822

1. The response of the coxal receptors of the crab Scylla serrata to step stretches consisted of a partial action potential, V, followed by a steady-state depolarization, V₈. The input resistance of the fibre was reduced during V₈.

2. In the absence of stimulation, the dendrites of the receptors depolarized when external Na⁺ was substituted with choline or Li⁺, and when the external K⁺ concentration was increased or decreased. The dendrites also depolarized when ouabain was added to the saline.

3. The amplitude of both V and V₈ was dependent on external Na⁺. In cells which were depolarized by ouabain, the amplitude of V₈ increased when the K⁺ concentration of the saline was reduced.

4. V₈ was followed by a small, but long-lasting, after-potential which was depolarizing when the membrane potential was between -70 and -60 mV. In cells depolarized by ouabain or by low K⁺ saline, the after-potential became hyperpolarizing.

5. When trains of brief stretches (each 5 ms in duration) were used as stimuli, the cells responded with trains of V responses. During this tetanic stimulation the cells hyperpolarized; cessation of the stimulus train was followed by a long-lasting hyperpolarization (PTH).

6. PTH was abolished in Li⁺ saline, in low K⁺ saline, and in the presence of ouabain. In control or in low K⁺ saline, PTH was not accompanied by a decrease in the input resistance of the fibres.

7. It is concluded that an electrogenic Na⁺ pump (or equivalent process) contributes a substantial fraction of the membrane potential of the unstimulated coxal receptors. Pump activity could be increased by Na⁺-loading the distal part of the cells with trains of V responses. By contrast, during the steady-state response to stretch, the pump was not activated.