Abstract
External ATP induces [3H] dopamine [( 3H]DA) release in rat pheochromocytoma cells (PC-12 cells). The ATP-induced release is a saturable process with half-effective concentration of EC50 = 80 microM. ADP is a poor secretagogue of [3H]DA (one-sixth of ATP) and AMP is devoid of secretory capabilities. Adenosine and the non-hydrolyzable analogues of ATP, AppNHp and AppCp are ineffective as inducers of [3H]DA, release, or as inhibitors of the ATP-induced [3H]DA release. The most potent antagonist of ATP-induced release is Coomassie Blue (IC50 = 25 microM), compared to ADP beta S (IC50 = 500 microM). The overall rank order of potency is ATP greater than ADP much greater than AMP greater than adenosine, which is characteristic of the P2-purinergic receptor. ATP-induced secretion is absolutely Ca2+ dependent, indicating an exocytotic process and is independent of Mg2+ (up to 2 mM) suggesting that the active species is not ATP4-. (a) The ATP-induced 45Ca2+ influx into the cells is in good correlation to ATP induction of release (IC50 = 80 and 90 microM, respectively) and is carried over to ADP which has a diminished ability to induce both release and 45Ca2+ influx. (b) Divalent cations (Ba2+ greater than Sr2+ greater than Ln3+ greater than Mn2+) replace Ca2+ and support ATP-induced release similar to their effectiveness in supporting bradykinin- and K+ (50 mM)-induced release in PC-12 cells (Weiss, C., Sela, D., and Atlas, D. (1990) Neurosci. Lett. 119, 241-245). Combined together the absolute requirement of [Ca2+]ex for release, inhibition of release by Gd3+ (IC50 = 100 microM), Ni2+, and Co2+ (IC50 = 1 mM), and support of release by Ba2+, Sr2+, and Mn2+, we suggest that ATP induces Ca2+ entry via ligand-operated Ca2+ channels as previously suggested for ATP in smooth muscle cells (Benham, C.D., Bolton, T.B., Byren, N.G., and Large, W.A. (1987) J. Physiol. (Lond.) 387, 473-488). No significant inhibition by 1 microM verapamil, 10 microM nifedipine, or 2 mM Cd2+ argues against ATP activation of voltage-dependent Ca2+ channels as similarly shown for ATP-induced [3H]noradrenaline release (Inoue, K., Nakazawa, K., Fujimoro, K., and Takanaka, A. (1989) Neurosci. Lett. 106, 294-299). Thus, the widely distributed ATP receptor might play an essential role in Ca2+ homeostasis of the cell by introducing Ca2+ into the cell via specific ligand-gated Ca2+ channels.
Highlights
From the Departmentof Biological Chemistry and TheOtto Loewi Center for Neurobiology, The Hebrew University of Jerusalem, Jerusalem 91904, &rue1
ATP exerts its effects via a specific receptor, the purinergic (P2)receptor, which is distinct from the adenosine(PI)recepsecretagogue of [3H]DA and AMP tor
Adenosine and the Since many studiehsave confirmed an ATP-selective non-hydrolyzableanalogues of ATP, AppNHp and action mediated via a unique ATP receptor (for review see ioCAAT(sIrCohptTAiopesacP0mTCsmo>P=pafio-sntAais5shhntir0Deeidepb0uPoBiiPctKnt>loe2eeMu>drn-fes)pfAt.eus(oTMaceIrfCntchiiPnrttvesaehe0e>tgreoi=goaovaAisnndec2Tiireiss5naPnrtadleoo-plbciufsn~sericAodnape)leunTtru,oc,sckPtoreewo-.mdolfiyhnrp[iddr3ca3CeuhHrHrcaeoi]]e2sdDfDd+ctpAAohro,deatrrAeelreeenpallDaeeccesPaaynteessBdeeiirSess.,nt,tcccmTBiaaeohualllncclcresiinruuwos(ommpBtifodheceea(Cnkn[gvhCa,etaa2rsa1rym+”i9e]-v7(;tdeHi)8yate,apoaic1rnfela9.an,lf7pcud1e9ieneu9t;rncm8iGtatt6oi-olK;o.sn,rBpn+deeeosa1ccnln9ihah,f9mitaa0c1tonmr)9cuin,8hbsei6aaeunln;nsctmBidernnedaepeTacalesrsstnreooiieptaionnhinAnn,adiT1gesnrma9eFtPersl8rcoai6eceo)(plet,S,thlmao1lmucur9untol9siagauvc0rrsleea)ee.:-t indicating anexocytotic process and is independent of al., 1985; Greenberg et al, 1988) in Erhrlich acites tumocrells
Summary
From the Departmentof Biological Chemistry and TheOtto Loewi Center for Neurobiology, The Hebrew University of Jerusalem, Jerusalem 91904, &rue. There is no direct evidence for the role of to ADP which has a diminished ability to induce both ATP-activatedchannels in neuronal cells, some release and45Ca2+influx. Sr2+> Ln3+> Mn2+)replace Ca2+ and support ATP- and Jessell,1983) and sensory neurons in the caudate trigeminduced release similar to their effectiveness in sup- inal nucleus (Salt and Hill, 1983) have shown excitation by porting bradykinin- and K+ (50 mM)-induced release externally applied ATP. It appears that ATP stimulates a in PC-12cells
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