Characterization of the adenosine receptors of the rat superior cervical ganglion

Abstract

1 Adenosine analogues caused hyperpolarization and inhibition of the depolarizing response to muscarine of the rat isolated superior cervical ganglion (SCG) measured by a 'grease gap' recording technique. The receptors mediating these responses have been characterized by use of a range of selective adenosine analogues and adenosine receptor antagonists. 2 In decreasing order of potency N6-cyclopentyladenosine (CPA), 2-chloroadenosine (2CA), adenosine, 2-phenylaminoadenosine (PAA), caused concentration-dependent hyperpolarizations whilst N6-(9-fluorenylmethyl)adenosine (PD 117,413) was inactive at up to 100 1M.3 The order of potency of adenosine analogues in depressing depolarization caused by a submaximal concentration of muscarine (100 nM) was: CPA> R-PIA = 2CA> NECA> S-PIA> BZA > adenosine> PAA, where R-and S-PIA = R(-)-and S(+)-N6-(2-phenylisopropyl)adenosine, NECA = 5'Nethylcarboxamidoadenosine and BZA = N6-benzyladenosine. PD 117,413 was inactive at concentrations up to 100 JIM. The maximum inhibitions of the muscarine-induced depolarization by CPA, 2CA, NECA and BZA were similar. R-PIA, S-PIA and PAA produced similar maximal inhibitions which were significantly smaller than those produced by CPA. 4 Hyperpolarizations caused by adenosine were antagonized by the P1-purinoceptor selective antagonist 1,3-dimethyl-8-phenylxanthine (8PT) and by the selective Al-adenosine receptor antagonist, 1,3-dipropyl-8-(4-((2aminoethyl)amino)carbonylmethyloxyphenyl)xanthine (XAC). Hyperpolarizations caused by CPA, adenosine and PAA were antagonized by the Al-selective antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) but not by the A2-selective antagonist, 3,7-dimethyl-1-propargylxanthine (DMPX). 5 Inhibition of the muscarinic-induced depolarization by CPA was antagonized by 8PT and DPCPX but not by DMPX.6 It is concluded that the neurones of the rat SCG possess PI-purinoceptors of the Al-adenosine receptor subtype which mediate hyperpolarization and inhibition of depolarization caused by muscarine.

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

“…The mechanism by which pyridoxal 5-phosphate containing compounds potentiate UTP-evoked depolarizations of the rat SCG remains obscure, but it is unlikely to be due to an antagonism of an opposing P2y-purinoceptor mediated hyperpolarization, because of the virtual absence of P2y-purinoceptors on the rat SCG (Connolly et al, 1993a). Interestingly, an enhancement of depolarizations of the rat SCG evoked by UTP was observed in the presence of the P2-purinoceptors antagonists, suramin (Connolly et al, 1993b) and reactive blue 2 .…”

“…The inability of pyridoxal 5-phosphate, PPADS or Iso-PPADS to alter responses evoked by sub-maximal concentrations of either adenosine (which activates P1-purinoceptors; Connolly et al, 1993a) or potassium (a nonspecific depolarizing agonist) suggests that these drugs do not antagonize Al-adenosine receptors or produce nonspecific effects on rat SCG neuronal membranes respectively. The inactivity of PPADS on adenosine-induced hyperpolarizations of the rat SCG is consistent with its reported lack of antagonism of Al-adenosine receptors on the rabbit vas deferens (Lambrecht et al, 1992).…”

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

“…The depression by ATP of the depolarizing response to muscarine was reduced by 8-PT suggesting that this action of ATP was also mediated via P,-purinoceptors. The depression of muscarinic depolarization by ATP is selective since depolarization by other agents such as GABA are not depressed by analogues of ATP (Table 2; Connolly, 1991). Indeed adenosine and ,Ty-MeATP slightly increased GABA-induced depolarization.…”

“…Similarly a reduction of [Ca2+]. from 2.5 to 0.1 mM did not alter the ability of DPCPX (8-cyclopentyl-1,3-dipropylxanthine, an Al-adenosine receptor antagonist) to shift the concentration-response curve for adenosine (Connolly, 1991). Overall, our observations suggest that low K+/Ca2" PSS is unlikely to alter qualitatively the antagonistic properties of 8-PT or suramin and provides a useful means of enhancing the sensitivity of the SCG to purines and pyrimidines.…”

“…Two concentration-response curves to a single purine were made on each ganglion, the first being the control responses followed by the response to the same adenosine analogue in the presence of 8-PT. The first and second concentration-response curves to adenosine were reproducible (Connolly, 1991). Responses caused by a given concentration of a purine in the absence and presence of antagonist were compared by Student's paired t test and P values were considered statistically significant if less than 0.05.…”