Action of purine and pyrimidine nucleotides on the rat superior cervical ganglion

Abstract

1 Using a grease-gap technique, we have investigated the effects of purine and pyrimidine nucleotides on the d.c. potential of the rat isolated superior cervical ganglion (SCG). 2 Of the purines tested, adenosine, adenosine 5'-triphosphate (ATP), P,y-methylene-adenosine 5'-triphosphate (P,y-MeATP) at up to 300 gM produced concentration-dependent hyperpolarizations, whereas 2-methyl-thio-ATP (2-Me.S.ATP) and a,p-methylene-ATP (a,,B-MeATP) depolarized ganglia. Of the pyrimidines tested, uridine 5'-triphosphate (UTP) produced concentration-dependent depolarizations and cytosine 5'-triphosphate (CTP) at 1000 tLM produced considerably smaller but significant depolarizations. In contrast uridine 5'-monophosphate (UMP) at 1000 AM hyperpolarized ganglia. The relative order of potency of purines and pyrimidines to depolarize ganglia was:-UTP> az,-MeATP>> CTP> 2-Me.S.ATP and to hyperpolarize ganglia was:-adenosine = P,By-MeATP> ATP> UMP.3 The ability of purines and pyrimidines to alter the depolarizing response caused by muscarine and of purines to alter depolarization induced by y-aminobutyric acid (GABA) was determined. The relative order of potency of nucleotides in depressing submaximal depolarization caused by muscarine (100 nM) was: adenosine = ATP>P,y-MeATP whereas 2-Me.S.ATP, a,4-MeATP and UTP did not significantly alter depolarization caused by muscarine. At 100ZM 3,Ty-MeATP and adenosine but not ATP potentiated GABA-induced depolarizations. 4 Hyperpolarizations caused by adenosine, ATP, P,y-MeATP and UMP and depolarizations caused by aj-MeATP were enhanced in medium containing reduced concentrations of calcium (0.1 mM) and potassium (2 mM). In this medium 8-phenyltheophylline abolished hyperpolarizations caused by adenosine and reversed hyperpolarizations caused by ATP into depolarizations. Suramin (300 tLM), a P2-purinoceptor antagonist, significantly reduced the depolarizing response caused by a,t-MeATP and significantly increased hyperpolarizations caused by ATP and ,B,-MeATP. Suramin (300 AM) did not significantly alter depolarizations caused by l,l-dimethyl-4-phenylpiperazinium (10 ILM), potassium (3 mM) or muscarine (100 nM) and significantly potentiated depolarizations caused by UTP (100IM).5 It is concluded that the rat SCG contains PI-purinoceptors that hyperpolarize the ganglion and diminish sensitivity to muscarine, and P2X-purinoceptors that depolarize the SCG. There is also some evidence to suggest the presence of receptors for UTP, i.e., pyrimidinoceptors, which depolarize SCG neurones.

Evidence from desensitization studies for distinct receptors for ATP and UTP on the rat superior cervical ganglion

“…This hypothesis is supported by the observation that prolonged application of UTP produced a concentrationdependent depression of subsequent responses to UTP but not responses mediated by x,4-Me-ATP, potassium or adenosine. Both the present observations and the inability of selective P2-purinoceptor antagonists to antagonize depolarizations of the rat SCG by UTP (Connolly et al, 1993;Connolly & Harrison, 1994) strongly indicate that these rat SCG neurones possess pyrimidinoceptors and support the idea that pyrimidinoceptors exist within the nervous system. I thank Dr P.J.…”

“…Some evidence for the presence of distinct P2-purinoceptors and pyrimidinoceptors on sympathetic neurones has been obtained by use of P2-purinoceptor antagonists, suramin (Connolly et al, 1993), pyridoxalphosphate-6-azophenyl-2',5'-disulphonic acid (Connolly & Harrison, 1994) and reactive blue 2 (unpublished observations) which selectively antagonized a,4-Me-ATP but not UTP-evoked depolarizations of the rat superior cervical ganglion (SCG). In order to assess whether purine and pyrimidine 5'-nucleotides activate distinct receptors on the rat SCG the effects of desensitization by UTP or a,-Me-ATP on responses evoked by these nucleotides was determined.…”

“…Methods Ganglia were prepared for recording of d.c. potentials via the internal carotid nerve and the body of the ganglion as described before (Connolly et al, 1993). SCG removed from male Sprague-Dawley rats (230-330 g) killed with a lethal dose of urethane were desheathed and placed in a recording bath and superfused (approx.…”

Differentiation by pyridoxal 5‐phosphate, PPADS and IsoPPADS between responses mediated by UTP and those evoked by α,β‐methylene‐ATP on rat sympathetic ganglia

“…In contrast both a,-Me-ATP and UTP depolarized rat SCG neurones and depolarizations elicited by UTP were not antagonized, rather they were enhanced in the presence of either suramin (a Present address: Biomedical Sciences Division, Physiology Group, King's College, Strand, London WC2R 2LS. P2X-purinoceptor antagonist) or reactive blue 2 (a P2Y-purinoceptor antagonist) (see Connolly et al, 1993b;Connolly & Harrison, 1994 respectively). Recently it has been proposed that pyridoxal 5-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) is a novel and selective antagonist of P2x-purinoceptors (Lambrecht et al, 1992;Ziganshin et al, 1993;McLaren et al, 1994) however, the effect of PPADS on UTP-mediated responses has yet to be reported.…”

“…Recently it has been proposed that neurones of the rat superior cervical ganglion (SCG) possess pyrimidinoceptors and that this preparation is a model tissue for the study of pyrimidinoceptors within the nervous system (Connolly & Harrison, 1993;Connolly et al, 1993b;Connolly, 1994a). This hypothesis was based upon the observation that there are distinct receptors that are activated by UTP but not by ATP or x, methylene adenosine 5'-triphosphate (m,-Me-ATP) (a selective P2X-purinoceptor agonist (Burnstock & Kennedy, 1985)).…”