Measurements on the Ionic Milieu of the Receptor Terminal in Mechanoreceptive Sensilla of Insects

Abstract

The active transport shown to occur at the sites of the epithelial receptors of insects — probably an electrogenous potassium transport — generates a voltage of 30 to 100 mV (outside positive). This electric source is, along with others, involved in the generation of the receptor potentials (Thurm, 1970, 1972, 1973). Furthermore, the transport should influence the ionic composition of the outer extracellular compartment (the receptor lymph cavity) which is delimited against the hemolymph by an epithelium of high ohmic resistance (Thurm, 1973). The ionic activities of the receptor lymph are implicated in receptor function (a) as they may influence the ionic composition of the receptor current and (b) by generating emfs according to the concentration gradients built up across the apical membranes of the sensory cell and of adjacent non-neural cells, respectively, across the sensory epithelium as a whole. To obtain some knowledge of the working conditions of the receptor cell, attempts have been made to determine the ionic activities within the receptor lymph cavity. This paper reports the results of our first series of measurements, concerning the potassium and the chloride activities.