Ionic basis of bioelectric currents during oogenesis in an insect

Transmembrane bioelectric currents around insect ovaries are well documented but as yet poorly understood. In the present study we describe the ionic basis of such currents around the telotrophic ovariole of Rhodnius prolixus using a two-dimensional vibrating probe and ion-substituted media and inhibitors. Current efflux from the base and apex of the terminal follicle is carried by electrogenic Na⁺ transport, and the return circuit over the middle of the terminal follicle is the result of Na⁺ influx/Cl⁻ efflux. We further show that a transient inward current at the apex of midvitellogenic terminal follicles is carried by Ca²⁺ ions and broadly correlates both spatially and temporally with trophic cord closure. A distinct current loop over the tropharium arises at the base via electrogenic Na⁺ efflux and returns over the middle and apical regions of the tropharium via Na⁺ and Ca²⁺ influx. These findings serve as a basis for the further dissection of the physiological relevance of transcellular ion currents around developing insect ovarian follicles.