Ligand-activated signal transduction in the 2-cell embryo.
Platelet-activating factor (PAF) is an autocrine trophic/survival factor for the preimplantation embryo. PAF induced an increase in intracellular calcium concentration ([Ca2+]i) in the 2-cell embryo that had an absolute requirement for external calcium. L-type calcium channel blockers (diltiazem, verapamil, and nimodipine) significantly inhibited PAF-induced Ca2+ transients, but inhibitors of P/Q type (omega-agatoxin; omega-conotoxin MVIIC), N-type (omega-conotoxin GVIA), T-type (pimozide), and store-operated channels (SKF 96365 and econazole) did not block the transient. mRNA and protein for the alpha1-C subunit of L-type channels was expressed in the 2-cell embryo. The L-type calcium channel agonist (+/-) BAY K 8644 induced [Ca2+]i transients and, PAF and BAY K 8644 each caused mutual heterologous desensitization of each other's responses. Depolarization of the embryo (75 mM KCl) induced a [Ca2+]i transient that was inhibited by diltiazem and verapamil. Whole-cell patch-clamp measurements detected a voltage-gated channel (blocked by diltiazem, verapamil, and nifedipine) that was desensitized by prior responses of embryos to exogenous or embryo-derived PAF. Replacement of media Ca2+ with Mn2+ allowed Mn2+ influx to be observed directly; activation of a diltiazem-sensitive influx channel was an early response to PAF. The activation of a voltage-gated L-type calcium channel in the 2-cell embryo is required for normal signal transduction to an embryonic trophic factor.
Lu
David P
DP
Human Reproduction Unit, Royal North Shore Hospital, University of Sydney, Sydney, New South Wales, 2065 Australia.
Li
Yan
Y
Bathgate
Roslyn
R
Day
Margot
M
O'Neill
Christopher
C
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001483:Base Sequence; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D002970:Cleavage Stage, Ovum / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D066298:In Vitro Techniques; D008024:Ligands; D008345:Manganese / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D018408:Patch-Clamp Techniques; D010972:Platelet Activating Factor / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D008024:Ligands; D010972:Platelet Activating Factor; D012333:RNA, Messenger; D008345:Manganese; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester