Large electrical currents traverse developing Ceropia follicles.

An intense (up to 20 muA/cm(2)) steady electrical current enters the anterior or nurse cell end of the growing follicle (or oocyte-nurse cell complex) of the Cecropia moth and is balanced by a more diffuse current leaving elsewhere. In late growth stages, the total transfollicular current is about 100 nA. Moreover, a separate small current, of about 1 nA, seems to leave the furrow between the oocyte and the nurse cells. After the nurse cells collapse, but before shell formation, the transfollicular current is redistributed so that a second relatively localized inward current appears at the posterior pole of the follicle. Thus, at this later stage currents enter both poles of the follicle and leave its sides. Previous measurements, with intracellular microelectrodes, seem to imply a very large (order of 1000 nA) back current across the cytoplasmic bridge between the oocyte and nurse cells. A simple model is presented that attributes the apparent bridge current, and the more directly measured transfollicular and furrow currents, to the action of an ion pump lying within the nurse cell face of the furrow membrane.