Vitellogenesis in the cockroach Nauphoeta cinerea: Separation of two classes of ovarian binding sites and calcium effects on binding and uptake

Two classes of vitellogenin binding sites with K_d-values of 7.3 nM and 290 nM were observed in follicle-membrane preparations of the cockroach Nauphoeta cinerea using a membrane-binding assay at pH 8. Separation of follicle cells and basal laminae from oocyte membranes prior to binding studies showed that the fraction consisting of follicle cells and basal laminae (FC/BL) contained high-affinity binding sites for vitellogenin (K_d=16.6 nM), whereas loweraffinity binding sites (K_d=200 nM) were found in the oocyte membrane fraction. The concentration of Ca²⁺ had a distinct effect on vitellogenin binding and uptake: maximal binding to the oocyte membrane fraction was observed at 0.3 mM Ca²⁺ and to the FC/BL fraction at 10 mM, whereas uptake of vitellogenin by oocytes in vitro was highest at 4 mM Ca²⁺. The calcium ionophore A23187 decreased vitellogenin uptake. This effect of A23187 could be counteracted by the calcium chelator Quin2. A hypothetical model for the uptake of vitellogenin into follicles of Nauphoeta cinerea is suggested.