Ca2+ responses to acetylcholine and adenosine triphosphate in the otocyst of chick embryo

Publisher Website
Google Scholar
Abstract
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 Ca2+-sensitive fluorescence measurements. Increases in [Ca2+]i were evoked by the bath application of acetylcholine (1 μM 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 Ca2+-free medium. The Ca2+ response to acetylcholine was mediated by muscarinic receptors. Atropine of 1 μM abolisehd the response to 10 μM acetylcholine; muscarine and carbamylcholine (100 μM each) evoked Ca2+ rises. Increases in [Ca2+]i were also evoked by the bath application of ATP (10 μM or higher). The Ca2+ rise by ATP was evoked even in a Ca2+-free medium. Adenosine (500 μM) did not cause any Ca2+ response. Suramin and reactive blue 2 (200 μM each) completely blocked the Ca2+ response to 500μM ATP. Uridine triphosphate (500 μM) caused comparable Ca2+ responses with those to 500 μM 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 μM and 100 μM, respectively). We conclude that undifferentiated cells in the otocyst epithelium have CaCa2+ mobilizing systems activated by acetylcholine and ATP. © 1995 John Wiley & Sons, Inc.