Expression of purinergic P2X2 receptor-channels and their role in calcium signaling in pituitary cells.
Pituitary cells express purinergic receptor-channels (P2XR), the activation of which by ATP is associated with the facilitation of Ca2+ influx. Pharmacological, RT-PCR, and nucleotide sequence analyses confirm the presence of a wild type P2X2aR and a spliced isoform P2X2bR, which lacks a portion of carboxyl terminal amino acids. Wild type and spliced isoform receptors have a similar EC50 for ATP and time-course for activation, but the spliced isoform exhibits rapid and complete desensitization, whereas the wild type channel desensitizes slowly and incompletely. Deletion and insertion studies have revealed that a 6 residue sequence located in carboxyl tail (Arg371-Pro376) is required for sustained Ca2+ influx through wild type receptors. When co-expressed, the wild type and spliced channels form functional heteropolymeric channels. The patterns of Ca2+ signaling in the majority of pituitary cells expressing ATP-gated receptor-channels are highly comparable to those observed in cells co-transfected with P2X2aR and P2X2bR. ATP-induced [Ca2+]i response in pituitary cells is partially inhibited by nifedipine, a blocker of voltage-gated L-type Ca2+ channels, suggesting that P2X2R not only drive Ca2+ into the cell, but also activate voltage-gated Ca2+ entry. Our results indicate that ATP represents a paracrine and (or) autocrine factor in the regulation of Ca2+ signaling, and that its actions are mediated in part by heteropolymeric P2X2R.
Stojilkovic
S S
SS
Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA. stankos@helix.nih.gov
Tomic
M
M
Van Goor
F
F
Koshimizu
T
T
D000255:Adenosine Triphosphate / Q000378:metabolism; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004594:Electrophysiology; D008969:Molecular Sequence Data; D009474:Neurons / Q000378:metabolism; D010902:Pituitary Gland / Q000378:metabolism*; D020033:Protein Isoforms; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D058476:Receptors, Purinergic P2X2; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection
C546401:P2RX2 protein, human; D020033:Protein Isoforms; D018048:Receptors, Purinergic P2; D058476:Receptors, Purinergic P2X2; D000255:Adenosine Triphosphate; D002118:Calcium