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

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 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.

Purinergic signalling during development and ageing

“…Release of Ca 2+ from intracellular stores is evoked in the otocyst epithelium of the early embryonic chick, incubated for 3 days (stage 18 to 19) [30] (Fig. 4), in developing chick myotubes [31] and in dissociated cells from whole early embryonic chicks [29,32].…”

Ca2+ responses to ATP via purinoceptors in the early embryonic chick retina.

“…1992;Abbracchio, Saffiey, H6pker & Burnstock, 1994;Neary, Whittemore, Zhu, Norenberg, 1994). ATP induces intracellular Ca2+ rises by Ca2+ release in astrocytes cultured fromii embryonic rat sp)in al corcd (Salter & Hicks, 1994, embryonic chick otocyst epitlheliumii (Nakaoka & Yamashita, 1995) acnd also in otlher dliffeientiatinig, cells (Higgublad & Heilbronn, 1988;Laasberg, 1990;Kubo, 1991;Lohmann et al 1991;Henning et al 1993). Such Ca2P mobilization caused by ATP could be an underlying mechanism for the mitogenic action of ATP, since intracellular Ca2P plays important roles in cellular proliferation (Berridge, 1993;Lauder, 1993).…”

“…ATP also acts on einbryonic or developing cells of nervous and non-nervous systems by increasing intracellular Ca2+ concentration ([Ca2+]1). Release of Ca2+ from intracellular Ca2P stores is evoked by ATP in the otocyst epithelium of the early embryonic chick (Nakaoka & Yamashita, 1995) and a mouse mesodermal stem cell line (Kubo, 1991). ATP increases inositol phosphates (InsPs) levels and raises [Ca2+]i in astrocytes cultured from embryonic rat spinal cord (Salter & Hicks, 1994, cultured neurones from embryonic rat brain (Mironov, 1994), myotubes cultured from embryonic chicks (Hiiggblad & Heilbronn, 1988), a murine myoblast cell line (Henning, Duin, den Hertog & Nelemans, 1993) and in the dissociated cells from whole early embryonic chicks (Laasberg, 1990;Lohmann, Drews, Donie & Reiser, 1991).…”

Early Expression of a Novel Nucleotide Receptor in the Neural Plate of Xenopus Embryos

“…This suggests that endogenous noradrenaline, acting via ␣-adrenergic receptors, is part of the mechanism controlling neuronal differentiation in the central nervous system. Very little is known about the roles of extracellular ATP in early embryonic development, but this molecule has been shown to cause an increase in intracellular Ca 2ϩ (Ca 2ϩ i ) 2 concentration in a number of embryonic cell types, including dissociated cells from early chick embryos (18), early embryonic chick otocyst (19) and retina (20), cultured astrocytes from embryonic rat spinal cord (21), cultured neurons from embryonic rat brain (22), myotubes cultured from embryonic chick (23), and a murine myoblast cell line (24). Increases in Ca 2ϩ i are known to regulate cell proliferation, migration, and differentiation (15,25), all important processes during embryonic development.…”