AJP - Cell Physiology, Vol 262, Issue 3 C635-C643, Copyright © 1992 by American Physiological Society
P2 purinergic receptors and cellular calcium metabolism in A 431 human epidermoid carcinoma cells
K. Hosoi, M. Fujishita, K. Sugita, K. Kurihara, T. Atsumi, T. Murai and T. Ueha
Department of Oral Physiology, Meikai University School of Dentistry, Saitama, Japan.
Stimulation of P2 purinergic receptors on A 431 human epidermoid cells with
ATP rapidly mobilized intracellular calcium and increased cytosolic free
Ca2+ ([Ca2+]i). Incorporation of 45Ca2+ was also stimulated by ATP at a
rate less than that of [Ca2+]i elevation. Among a number of nucleosides,
nucleotides, and their analogues examined, ATP, GTP, UTP, ADP, UDP,
adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S), and
5'-adenylylimidodiphosphate (AMP-PNP) increased both [Ca2+]i and 45Ca2+
influx, whereas others did not; these latter two analogues (ATP gamma S and
AMP-PNP) blocked the ATP-stimulated 45Ca2+ influx only very slightly,
suggesting that they are not prominent antagonists but rather agonists. A
high correlation between [Ca2+]i increase and 45Ca2+ influx, in terms of
nucleotide specificity, suggests the involvement of [Ca2+]i in influx of
45Ca2+. It appeared that [Ca2+]i elevated by several nucleotides or
nucleotide analogues opened a calcium gate, thus allowing the influx of
45Ca2+. P2 purinergic receptors on these cells had such a characteristic
that they were rapidly desensitized. These nucleotides or analogues also
affected epidermal growth factor (EGF) receptors by inhibiting the EGF
binding. The differences of ligand or substrate specificities between P2
purinergic receptors and ecto-nucleotidases indicates that the two
components are different molecules involved in different systems.
