Synergistic interactions between human transfected adenosine A1 receptors and endogenous cholecystokinin receptors in CHO cells.
The effect of Gi coupled receptor activation (adenosine A1 and 5-HT1B receptors) on cholecystokinin receptor-stimulated inositol phosphate accumulation has been investigated in Chinese hamster ovary cells transfected with the human adenosine A1 receptor cDNA (CHO-A1). CHO cells constitutively express the 5-HT1B receptor [Berg, Clarke, Sailstad, Saltzman and Maayani (1994) Mol. Pharmacol. 46, 477-484]. Our previous studies using CHO-A1 cells have revealed that both the adenosine A1 and 5-HT1B receptor are negatively coupled to adenylyl cyclase activity and stimulate increases in [Ca2+]i, through a pertussis toxin-sensitive pathway. In the present study the selective adenosine A1 receptor agonist N6-cyclopentyladenosine stimulated a pertussis toxin-sensitive increase in total [3H]inositol phosphate accumulation. The sulphated C-terminal octapeptide of cholecystokinin (CCK-8) stimulated a robust and pertussis toxin-insensitive increase in [3H]inositol phosphate accumulation through the activation of CCKA receptors. Co-stimulation of CHO-A1 cells with N6-cyclopentyladenosine and CCK-8 produced a synergistic increase in [3H]inositol phosphate accumulation. The synergistic interaction between N6-cyclopentyladenosine and CCK-8 was abolished in pertussis toxin-treated cells. Synergy between N6-cyclopentyladenosine and CCK-8 still occurred in the absence of extracellular calcium. The 5-HT1B receptor agonist 5-carboxyamidotryptamine did not stimulate a measurable increase in [3H]inositol phosphate accumulation. Furthermore, 5-carboxyamidotryptamine had no significant effect on CCK-8 mediated [3H]inositol phosphate production. Activation of endogenous P2U receptors (Gq/Gll coupled) with ATP gamma S produced a significant increase in [3H]inositol phosphate accumulation. Co-stimulation of CHO-A1 cells with ATP gamma S and CCK-8 produced additive increases in [3H]inositol phosphate accumulation. These data indicate that CHO-A1 cells may prove a useful model system in which to investigate further the mechanisms underlying the intracellular 'cross-talk' between phospholipase C coupled receptors (Gq/Gll linked) and Gi/Go coupled receptors.
Dickenson
J M
JM
Department of Physiology and Pharmacology, Medical School, Queen's Medical Centre, Nottingham, UK. mqzjmd@mqnl.phpharm.nottingham.ac.uk
Hill
S J
SJ
D000241:Adenosine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology; D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D001570:Benzodiazepinones / Q000494:pharmacology; D016466:CHO Cells / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D006224:Cricetinae; D020109:Devazepide; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D006727:Hormone Antagonists / Q000494:pharmacology; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism*; D037342:Pertussis Toxin; D011377:Proglumide / Q000031:analogs & derivatives / Q000494:pharmacology; D018047:Receptors, Purinergic P1 / Q000378:metabolism* / Q000502:physiology; D011985:Receptors, Serotonin / Q000378:metabolism* / Q000502:physiology; D012844:Sincalide / Q000494:pharmacology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D001570:Benzodiazepinones; D006727:Hormone Antagonists; D007295:Inositol Phosphates; D018047:Receptors, Purinergic P1; D011985:Receptors, Serotonin; D010566:Virulence Factors, Bordetella; C048599:N(6)-cyclopentyladenosine; D037342:Pertussis Toxin; D011377:Proglumide; D020109:Devazepide; D000241:Adenosine; C048181:lorglumide; D012844:Sincalide; D002118:Calcium