Meiosis reinitiation of mussel oocytes involves L-type voltage-gated calcium channel

In the present work we assessed the involvement of L-type voltage opening Ca2+ channels in KCl-induced meiosis reinitiation of metaphase-arrested blue mussel (Mytilus galloprovincialis) oocytes by performing binding assays with a tritiated dihydropyridine analog (+)PN 200110. Our data reveal the existence of a single class of dihydropyridine receptors in plasma membrane-enriched rough microsome preparations of mussel oocytes. The apparent affinity (Kd) of characterized receptors equals 1.32 +/- 0.21 microM while their maximal binding capacity (Bmax) is 620 +/- 150 pmol/mg protein. The comparison of the rank order of potency of analogs tested to: 1) inhibit [(+)-[3H]PN 200110 specific binding and 2) block KCl-induced meiosis reinitiation pointed to the pharmacological profile similar to but not identical with those previously described for mammalian dihydropyridine receptors. The efficiencies of all antagonists tested are linearly related (r = 0.995) in binding-(inhibition of [(+)-[3H]PN 200110 specific binding) and biological (inhibition of meiosis reinitiation) assays thus arguing for functional involvement of L-type Ca2+ channels in oocyte activation. Reversibility of antagonist actions on meiosis reinitiation and dependence of receptor binding characteristics on a membrane polarization state further suggested such a role.