Two distinct cytosolic calcium responses to extracellular ATP in rat parotid acinar cells.
1. Increasing concentrations of ATP (0.5 microM-300 microM) produced a biphasic increase in intracellular calcium concentration [Ca]i in rat parotid acinar cells, reflecting two distinct Cai responses to extracellular ATP. 2. In the absence of Mg2+ (with 3 mM CaCl2 in the buffer solution), the more sensitive response was maximal at 3-5 microM and was not further increased by 30 microM ATP. This response to ATP was not well maintained and was blocked by ADP (0.5 mM). A second, much larger increase in Cai was observed on addition of 300 microM ATP. This larger effect, which we have described previously, appears to be mediated by ATP4-, and was selectively reversed by 4,4'-di-isothiocyanato-dihydrostilbene-2,2'-disulphonate as well as by high concentrations of alpha,beta-methylene ATP. 3. Among ATP analogues, only the putative P2Z agonist, 3'-0-(4-benzoyl)benzoyl-ATP distinguished between the two responses. This analogue was at least 10 fold more potent than ATP in stimulating the ATP(4-)-response, but did not evoke the more sensitive response. The agonist potency series for both responses to ATP was identical for other analogues examined (ATP > ATP gamma S = 2-methylthio ATP (a P2y-selective agonist) >> ADP, ITP and alpha,beta-methylene ATP (a P2x-selective agonist)). 4. Although the effect of ATP4- could best be characterized as a P2z-type purinoceptor response, this effect was strongly and selectively blocked by reactive blue 2, a putative P2y-purinoceptor antagonist. Reactive blue 2 may bind to and block P2z purinoceptors since [gamma 32P]-ATP binding to parotid cells was inhibited by this compound. 5. In contrast to the response to ATP4-, the more sensitive response to ATP was potentiated by 2+ reactive blue 2 and was less affected by increases in external Mg2+ and Ca2+.6. Parasympathetic denervation selectively increased the more sensitive response, suggesting that it maybe physiologically regulated.
McMillian
M K
MK
Neuroscience Programe, Tufts University School of Medicine, Boston, Massachusetts 02111.
Soltoff
S P
SP
Cantley
L C
LC
Rudel
R
R
Talamo
B R
BR
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D003714:Denervation; D008297:Male; D010275:Parasympathetic Nervous System / Q000502:physiology*; D010306:Parotid Gland / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011983:Receptors, Purinergic / Q000187:drug effects*; D012680:Sensitivity and Specificity
D011983:Receptors, Purinergic; D000255:Adenosine Triphosphate; D002118:Calcium