title: Characterization of the Ca2+ influx into embryonic cells after stimulation of the embryonic muscarinic receptor.
abstract: Embryonic cells transiently express an embryonic muscarinic system during morphogenesis. Stimulation of the embryonic muscarinic receptor results in biphasic intracellular Ca2+ mobilization: an initial "peak" due to Ca2+ release from intracellular stores is followed by a sustained "plateau" of enhanced cytoplasmic Ca2+ due to influx of extracellular Ca2+. In the present investigation, we characterized the Ca2+ influx by measuring the cytoplasmic free Ca2+ concentration [Ca2+]i using the Ca2+ indicator fura-2: 1. The increase of [Ca2+]i during the plateau depended linearly on the logarithm of the extracellular calcium concentration whereas the initial peak was almost independent from extracellular calcium. 2. The organic Ca2+ entry blockers verapamil, gallopamil, nifedipine, nitrendipine and the inorganic blockers Mn2+, Mg2+ and La3+ were without effect on both phases of Ca2+ mobilization. Only Ni2+ at concentrations above 1 mM was able to reduce the influx without affecting the intracellular Ca2+ release. 3. Substitution of extracellular Na+ by guanidine+, choline+ or tris+ and membrane depolarisation by increasing the extracellular K+ concentration had no effect on either phase of Ca2+ mobilization. We conclude that a non-voltage dependent, receptor-operated influx mechanism, probably a "second messenger operated Ca2+ channel", is responsible for the Ca2+ influx after stimulation of the embryonic muscarinic receptor.
authors.affiliation: Institute of Anatomy, University of Tübingen, Federal Republic of Germany.
authors.forename: G
authors.initials: G
authors.lastname: Oettling
authors.forename: U
authors.initials: U
authors.lastname: Götz
authors.forename: U
authors.initials: U
authors.lastname: Drews
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology; D002478:Cells, Cultured / Q000187:drug effects; D002642:Chick Embryo; D003593:Cytoplasm / Q000378:metabolism; D004622:Embryo, Mammalian / Q000378:metabolism*; D004625:Embryo, Nonmammalian; D016257:Fura-2; D011188:Potassium / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000187:drug effects* / Q000378:metabolism; D015290:Second Messenger Systems
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D011976:Receptors, Muscarinic; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium; D016257:Fura-2