MEIOSIS REINITIATION OF MUSSEL OOCYTES INVOLVES L-TYPE VOLTAGE-GATED CALCIUM-CHANNEL

In the present work we assessed the involvement of L-type voltage open ing Ca2+ channels in KCI-induced meiosis reinitiation of metaphase-arr ested blue mussel (Mytilus galloprovincialis) oocytes by performing bi nding assays with a tritiated dihydropyridine analog (+)PN 200110. Our data reveal the existence of a single class of dihydropyridine recept ors in plasma membrane-enriched rough microsome preparations of mussel oocytes. The apparent affinity (K-d) of characterized receptors equal s 1.32 +/- 0.21 mu M while their maximal binding capacity (B-max) is 6 20 +/- 150 pmol/mg protein. The comparison of the rank order of potenc y of analogs tested to: i) inhibit [(+)-[H-3]PN 200110 specific bindin g and 2) block KCl-induced meiosis reinitiation pointed to the pharmac ological profile similar to but not identical with those previously de scribed for mammalian dihydropyridine receptors. The efficiencies of a ll antagonists tested are linearly related (r = 0.995) in binding-(inh ibition of [(+)-[H-3]PN 200110 specific binding) and biological (inhib ition of meiosis reinitiation) assays thus arguing for functional invo lvement 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 sugg ested such a role. (C) 1997 Wiley-Liss, Inc.