Evidence for a new subtype of serotonin receptor in oocytes of the surf clam Spisula solidissima.
The neurohormone serotonin 5-hydroxytryptamine (5-HT) triggers meiotic reinitiation in prophase-arrested oocytes of Spisula solidissima (Hirai et al., J. Exp. Zool. 245, 318-321, 1988). The original pharmacological profile of this oocyte response (Krantic et al., Dev. Biol. 146, 491-498, 1991) suggested a novel 5-HT receptor subtype. The present study employed [3H]5-HT binding assays to characterize these putative receptors. Kinetics of [3H]5-HT equilibrium binding saturation revealed that vitellin-deprived oocyte plasma membranes contained a homogeneous population of 5-HT-specific binding sites with an apparent affinity of 0.21 +/- 0.03 microM and maximal binding capacity of 1.22 +/- 0.62 pmol/mg protein. Analysis of [3H]5-HT-specific binding inhibition by various 5-HT-related compounds yielded a novel pharmacological profile for these binding sites. Moreover, the efficacies of most compounds in inhibiting the specific binding upon 5-HT membrane sites correlated with their efficacies in either triggering meiotic reinitiation (for agonists) or inhibiting the 5-HT-induced oocyte response (for antagonists). Such a correlation indicates that 5-HT binding sites located in the plasma membrane represent the physiological receptors involved in transduction of the biological effects of 5-HT in Spisula solidissima oocytes.
Krantic
S
S
Laboratoire de Biologie Moléculaire et Cellulaire, UMR49 Centre National de la Recherche Scientifique et Ecole Normale Supérieure de Lyon, France.
Dubé
F
F
Guerrier
P
P
D000818:Animals; D049872:Bivalvia / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology; D007700:Kinetics; D008540:Meiosis / Q000502:physiology; D009865:Oocytes / Q000737:chemistry* / Q000187:drug effects; D011869:Radioligand Assay; D011985:Receptors, Serotonin / Q000032:analysis* / Q000187:drug effects; D012701:Serotonin / Q000378:metabolism*
D011985:Receptors, Serotonin; D012701:Serotonin