ACTIVATION OF A CA-OOCYTE SYNCYTIUM OF DYSDERCUS-INTERMEDIUS(+ CURRENT COINCIDES WITH THE ONSET OF OOCYTE DIFFERENTIATION IN THE LARVAL TELOTROPHIC TROPHOCYTE)

Between the two compartments of the telotrophic-meroistic trophocyte-o ocyte syncytium isolated from early fifth instar larvae of Dysdercus i ntermedius (Heteroptera: Pyrrhocoridae), no differences in the resting membrane potentials (E-m=-18.3 mV for lateral trophocytes E-m = - 19. 2 mV for presumptive oocytes) were recorded. Transition of the presump tive oocyte into a differentiating oocyte during the fifth instar coin cides with comprehensive changes in the syncytium: (1) lateral trophoc yte and differentiating oocyte hyperpolarize; (2) hyperpolarization in the trophocyte is stronger than in the oocyte resulting in a potentia l difference of Delta E-m = -12.8 mV (ooplasm positive) across the syn cytium; (3) activities in cytoplasmic calcium (aCa(++)) drop more stro ngly in the lateral trophocytes than in the differentiating oocyte so that a calcium gradient is established in the syncytium during oocyte transition. Linked up with results reported earlier, these observation s imply the activation of a larval calcium current before the differen tiation of a presumptive oocyte.