Ca2+ responses to acetylcholine and adenosine triphosphate in the otocyst of chick embryo.
The action of acetylcholine and adenosine triphosphate (ATP) on cytoplasmic Ca2+ concentration ([Ca2+]i) was studied in the otocyst epithelium of embryonic day 3 chicks with Ca(2+)-sensitive fluorescence measurements. Increases in [Ca2+]i were evoked by the bath application of acetylcholine (1 microM or higher). The rise in [Ca2+]i was due to the release of Ca2+ from intracellular Ca2+ stores, since the Ca2+ response occurred even in a Ca(2+)-free medium. The Ca2+ response to acetylcholine was mediated by muscarinic receptors. Atropine of 1 microM abolished the response to 10 microM acetylcholine; muscarine and carbamylcholine (100 microM each) evoked Ca2+ rises. Increases in [Ca2+]i were also evoked by the bath application of ATP (10 microM or higher). The Ca2+ rise by ATP was evoked even in a Ca(2+)-free medium. Adenosine (500 microM) did not cause any Ca2+ response. Suramin and reactive blue 2 (200 microM each) completely blocked the Ca2+ response to 500 microM ATP. Uridine triphosphate (500 microM) caused comparable Ca2+ responses with those to 500 microM ATP. These results suggested the involvement of P2U purinoceptors. The potentiation of Ca2+ rise was observed when acetylcholine and ATP were co-applied at submaximal concentrations (10 microM and 100 microM, respectively). We conclude that undifferentiated cells in the otocyst epithelium have Ca2+ mobilizing systems activated by acetylcholine and ATP.
Nakaoka
Y
Y
Department of Physiology, Osaka University Medical School, Suita, Japan.
Yamashita
M
M
D000109:Acetylcholine / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002642:Chick Embryo; D004305:Dose-Response Relationship, Drug; D007758:Ear, Inner / Q000187:drug effects* / Q000196:embryology; D004848:Epithelium / Q000187:drug effects / Q000196:embryology; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology; D018048:Receptors, Purinergic P2 / Q000187:drug effects
D011976:Receptors, Muscarinic; D018048:Receptors, Purinergic P2; D000255:Adenosine Triphosphate; D000109:Acetylcholine; D002118:Calcium