Selective activation of Ca2+ influx by extracellular ATP in a pancreatic beta-cell line (HIT).
The action of exogenous ATP on cytoplasmic free Ca2+ ([Ca2+]i) was studied in insulin secreting cells using fura-2. Stimulation of clonal pancreatic beta-cells (HIT) with ATP (range 2-20 microM) evoked a sustained elevation in [Ca2+]i. ATP selectively promoted Ca2+ influx and not Ca2+ mobilization since (1) the effect required external Ca1+ and (2) was observed in cells in which internal stores were depleted with ionomycin (3) the rate of Mn2+ influx, measured as the quenching of the fura-2 signal, was accelerated by ATP. The action of ATP was unaffected by the voltage-sensitive Ca2+ channel blockers nifedipine and verapamil as well as by a depolarizing concentration of K+. The effect on [Ca2+]i was highly specific for ATP since AMP, ADP, adenosine 5'-[gamma-thio]triphosphate, adenosine 5'-[beta, gamma-methylene]triphosphate, GTP and adenosine were ineffective. In normal pancreatic islet cells, both exogenous ATP (range 0.2-2 microM) and ADP induced a transient Ca2+ elevation that did not require external Ca2+. The nucleotide specificity of the effect on [Ca2+]i suggests that ATP activates P2 gamma purinergic receptors in normal beta-cells. Thus, ATP evokes a Ca2+ signal in clonal HIT cells and normal islet cells by different transducing systems involving distinct purinoreceptors. A novel mechanism for increasing [Ca2+]i by extracellular ATP is reported in HIT cells, since the nucleotide specificity and the selective activation of Ca2+ influx without mobilization of internal Ca2+ stores cannot be explained by mechanisms already described in other cell systems.
Geschwind
J F
JF
Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia.
Hiriart
M
M
Glennon
M C
MC
Najafi
H
H
Corkey
B E
BE
Matschinsky
F M
FM
Prentki
M
M
D000227:Adenine Nucleotides / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D004987:Ethers / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D015759:Ionomycin; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014700:Verapamil / Q000494:pharmacology
D000227:Adenine Nucleotides; D001572:Benzofurans; D015220:Calcium Channels; D004987:Ethers; D005456:Fluorescent Dyes; D007328:Insulin; D004533:Egtazic Acid; D015759:Ionomycin; D000255:Adenosine Triphosphate; D002217:Carbachol; D014700:Verapamil; D009543:Nifedipine; D011188:Potassium; D002118:Calcium; D016257:Fura-2