CA2-TRIPHOSPHATE IN THE OTOCYST OF CHICK-EMBRYO( RESPONSES TO ACETYLCHOLINE AND ADENOSINE)

The action of acetylcholine and adenosine triphosphate (ATP) on cytopl asmic Ca2+ concentration ([Ca2+](i)) was studied in the otocyst epithe lium of embryonic day 3 chicks with Ca2+-sensitive fluorescence measur ements. Increases in [Ca2+](i) were evoked by the bath application of acetylcholine (1 mu M or higher), The rise in [Ca2+](i) was due to the release of Ca2+ from intracellular Ca2+ stores, since the Ca2+ respon se occurred even in a Ca2+-free medium. The Ca2+ response to acetylcho line was mediated by muscarinic receptors. Atropine of 1 mu M abolishe d the response to 10 mu M acetylcholine; muscarine and carbamylcholine (100 mu M each) evoked Ca2+ rises. Increases in [Ca2+](i) were also e voked by the bath application of ATP (10 mu M 01. higher). The Ca2+ ri se by ATP was evoked even in a Ca2+-free medium. Adenosine (500 mu M) did not cause any Ca2+ response. Suramin and reactive blue 2 (200 mu M each) completely blocked the Ca2+ response to 500 mu M ATP, Uridine t riphosphate (500 mu M) caused comparable Ca2+ responses with those to 500 mu M ATP. These results suggested the involvement of P-2U purinoce ptors. The potentiation of Ca2+ rise was observed when acetylcholine a nd ATP were co-applied at submaximal concentrations (10 mu M and 100 m u M, respectively), We conclude that undifferentiated cells in the oto cyst epithelium have Ca2+ mobilizing systems activated by acetylcholin e and ATP. (C) 1995 John Wiley & Sons, Inc.