Steady-state gradient in calcium ion activity across the intercellular bridges connecting oocytes and nurse cells in Hyalophora cecropia.
Intracellular activities of K+, H+, Mg2+, Ca2+, and Cl-, measured with ion selective microelectrodes in the oocyte and the nurse cells in ovarian follicles of Hyalophora cecropia, indicated that a Ca2+ current is a key component of the electrical potential that is maintained across the intercellular bridges connecting these two cells. In vitellogenic follicles, Ca2+ activity averaged 650 nM in the oocyte and 190 nM in the nurse cells, whereas activities of the other ions studied differed between these cells by no more than 6%. Incubation in 200 microM ammonium vanadate caused a reversal of electrical potential from 8.3 mV, nurse cell negative, to 3.0 mV, oocyte negative, and at the same time the Ca2+ gradient was reversed: activities rose to an average 3.0 microM in the nurse cells and 1.6 microM in the oocyte, whereas transbridge ratios of the other cations remained at 0-3%. In immature follicles that had not yet initiated their transbridge potentials, Ca2+ activities averaged approximately 2 microM in both oocyte and nurse cells. The results suggest that vitellogenic follicles possess a vanadate-sensitive Ca2+ extrusion mechanism that is more powerful in the nurse cells than in the oocyte.
Woodruff
R I
RI
Department of Biology, West Chester University, PA 19383.
Telfer
W H
WH
D000818:Animals; D001386:Azides / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D005260:Female; D007365:Intercellular Junctions / Q000378:metabolism; D017136:Ion Transport / Q000502:physiology; D008274:Magnesium / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D009036:Moths / Q000166:cytology / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D006080:Ovarian Follicle / Q000166:cytology / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D019810:Sodium Azide; D014638:Vanadates / Q000494:pharmacology
D001386:Azides; D002712:Chlorides; D014638:Vanadates; D019810:Sodium Azide; D008274:Magnesium; D011188:Potassium; D002118:Calcium