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Mechanism Underlying the ATP‐Induced Increase in the Cytosolic Ca 2+ Concentration in Chick Ciliary Ganglion Neurons
Author(s) -
Sorimachi Masaru,
Abe Yumiko,
Furukawa Katsutoshi,
Akaike Norio
Publication year - 1995
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1995.64031169.x
Subject(s) - biophysics , chemistry , cytosol , fura 2 , depolarization , ouabain , channel blocker , membrane potential , sodium , calcium , biochemistry , biology , enzyme , organic chemistry
We examined the mechanism underlying the ATP‐induced increase in the cytosolic Ca 2+ concentration ([Ca] in ) in acutely isolated chick ciliary ganglion neurons, using fura‐2 microfluorometry. The ATP‐induced increase in [Ca] in was dependent on external Ca 2+ , was blocked in a dose‐dependent manner by reactive blue 2, and was substantially inhibited by both L‐ and N‐type Ca 2+ channel blockers. ATP was effective in increasing [Ca] in in the presence of a desensitizing concentration of nicotine (100 µ M ), and simultaneous addition of maximal doses of ATP and nicotine caused an additive increase in [Ca] in , suggesting that ATP acts on a site distinct from nicotinic acetylcholine receptors. ATP also increased the cytosolic Na + concentration as determined by sodium‐binding benzofuran isophthalate microfluorometry. These results suggest that ATP increases Na + influx through P 2 purinoceptor‐associated channels resulting in membrane depolarization, which in turn increases Ca 2+ influx through voltage‐dependent Ca 2+ channels. However, ATP still caused a small increase in [Ca] in under Na + ‐free conditions, and this [Ca] in increase was little affected by Ca 2+ channel blockers. ATP also increased Mn 2+ influx under Na + ‐free conditions, as indicated by quenching of fura‐2 fluorescence. These results suggest that nonselective cationic channels activated by ATP are permeable not only to Ca 2+ but also to Mn 2+ , in addition to monovalent cations.