ABSTRACT
Ovarioles of the African migratory locust (Locusta migratoria) are of the panoistic type, where each oocyte is surrounded by a layer of follicle cells, and a single ovariole forms a longitudinal chain of ‘follicles’ held together by an ovariole sheath. In an earlier publication (Wollberg, Cohen & Kalina, 1976) we demonstrated that in this species, a potential difference exists across the ‘follicle’ wall (defined hereafter as ‘oocyte potential’), ranging between 30 and 55 mV (inside oocyte negative in respect to external grounded medium), with the more mature oocytes possessing larger potential differences than the less-mature oocytes. We have also shown that all the follicles along a single ovariole were electrotonically and histologically coupled by oocyte follicle cell gap junctions. The ionic basis of oocyte and egg potentials have been investigated in several animal species, invertebrates and vertebrates (e.g. Powers & Tupper, 1975; Miyazaki & Hagiwara, 1976; Shen & Steinhardt, 1976; Ziegler & Morrill, 1977). In most of these cases, oocyte membrane potentials were determined, primarily, by the passive distribution of potassium ions and to a lesser extent by sodium ions. For some species the involvement of an undefined metabolic electrogenic pump, in maintaining the steady-state oocyte potential, was proposed (Powers & Tupper, 1975; Miyazaki & Hagiwara, 1976; Ziegler & Morrill, 1977). In the present report we show that the steady-state oocyte potential of Locusta migratoria is mainly determined by the passive distribution of potassium ions and by an ouabain-sensitive electrogenic Na/K pump.
