Extracellular ATP activates calcium entry and mobilization via P2U-purinoceptors in rat lactotrophs.
Extracellular ATP has been previously shown to activate calcium signalling in pituitary cell populations [1] but the particular cell types involved have not been identified. We used video imaging of Fura-2 loaded into single rat pituitary cells and identified as lactotrophs to study the effects of extracellular ATP on [Ca2+]i. ATP does not permeabilize the cells as shown by exclusion of propidium iodide. ATP causes two types of calcium transients in lactotrophs. The most common response is a rapid increase in [Ca2+]i that decays slowly and is terminated by washout of ATP. This type of response is also seen in calcium-free medium, demonstrating mobilization of calcium stores dependent upon the presence of the agonist. ATP also stimulates calcium entry as detected by Mn(2+)-quenching of Fura-2. ATP in Mg(2+)-free medium and ATP gamma S are effective agonists suggesting ATP4- is the active form. The presence of P2-purinoceptors is apparent because ATP, ADP and AMP increase [Ca2+]i in decreasing order of potency and adenosine has no effect. ATP-induced calcium transients are reduced by the P2-purinoceptor antagonists suramin and quinidine. UTP is equipotent with ATP and defines the receptor subtype as P2U. We conclude that ATP4- acts on rat lactotrophs via P2U-purinoceptors to elevate [Ca2+]i from intracellular and extracellular sources.
Carew
M A
MA
Department of Neurobiology, Babraham Institute, Cambridge, UK.
Wu
M L
ML
Law
G J
GJ
Tseng
Y Z
YZ
Mason
W T
WT
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D005260:Female; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000378:metabolism*
D018048:Receptors, Purinergic P2; D000255:Adenosine Triphosphate; D002118:Calcium