. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CALMODULIN AND SPISULA OOCYTES 45 RESULTS Calmodulin antagonists can block GVBD Since KC1 induces GVBD rapidly and synchronously in oocytes in this species, and KCl-induced GVBD would be independent of possible indirect inhibition through inhibition of fertilization, we initially tested the ability of calmodulin antagonists to prevent GVBD on KCl-activated oocytes. Figure 1 shows that all calmodulin antag- onists tested blocked GVBD in Spisula oocytes when induced by KC1. The results also show that calmidazolium is maximally
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CALMODULIN AND SPISULA OOCYTES 45 RESULTS Calmodulin antagonists can block GVBD Since KC1 induces GVBD rapidly and synchronously in oocytes in this species, and KCl-induced GVBD would be independent of possible indirect inhibition through inhibition of fertilization, we initially tested the ability of calmodulin antagonists to prevent GVBD on KCl-activated oocytes. Figure 1 shows that all calmodulin antag- onists tested blocked GVBD in Spisula oocytes when induced by KC1. The results also show that calmidazolium is maximally effective at ca. 3 v-M, a substantially lower effective concentration than observed for chlorpromazine or W-7 (ca. 50-75 ), and that W-5 is ineffective at concentrations up to 200 \iM. We also tested the effects of calmodulin antagonists on GVBD when induced by fertilization, the natural trigger in this species. Figure 2 shows that all calmodulin antagonists tested inhibited GVBD when induced by fertilization. Furthermore, the effective concentrations of the antagonists for fertilization-induced GVBD were similar to those for KCl-induced GVBD. Calmidazolium was maximally effective at ca. 3-10 nAf, chlorpromazine and W-7 were maximally effective at ca. 75 ^M, and W-5 was ineffective at any concentration up to 200 \iM. The antagonists had no effect on post-GVBD development through first cleavage, because oocytes which successfully underwent GVBD in the presence of the inhibitors after fertilization also formed polar bodies and cleaved normally and synchronously with controls. To determine the period of sensitivity to calmodulin antagonists for inhibition of GVBD, KCl-stimulated oocytes were exposed to 100 nM W-7 at various times after KC1 stimulation and examined for GVBD 20 min later. Figure 3 shows that GVBD was prevented only if W-7 was added within 1 min after KC1 addition. Similar results were obtained using calmidazolium (data not shown). o CD > e? UJ O rr 100 80 - 6
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