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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.

1 The effect of pyridoxal 5-phosphate, and the 2',4' and 2',5'-disulphonic acid isomers of 6-azophenylpyridoxal 5-phosphate (PPADS and IsoPPADS respectively) on depolarization of the rat superior cervical ganglion evoked by a,-methylene-adenosine 5'-triphosphate (a,-Me-ATP) and uridine 5'-triphosphate (UTP) were determined by a grease-gap recording technique.2 Pyridoxal 5-phosphate (10-100 tM) and PPADS (10-100 M) enhanced UTP-and depressed a,-

Extracellular purines have essential roles in neuronal development; hence, disruptions in their metabolism as reported in Lesch Nyhan syndrome (LNS) could result in developmental abnormalities. The deficiency of hypoxanthine-guanine phosphoribosyl transferase (HGPRT) in LNS leads to increased hypoxanthine and uric acid production. We have reported that HGPRT-deficient B103-4C neuroblastoma, a neuronal model of LNS, proliferated less and differentiated more than their HGPRT-positive B103 counterparts. Here, we sought to determine whether differences in proliferation and differentiation would occur when these cells were cultured in the presence of hypoxanthine or in a hypoxanthine-/serum-free chemically defined media (NBMN2). In media with 1% serum, hypoxanthine (50 microM) significantly increased the proliferation of both cell lines with a greater effect on B103-4C cells. In 1% serum media, hypoxanthine increased differentiation of B103 but decreased B103-4C differentiation. In NBMN2, B103 proliferated far more than B103-4C, but both cell types differentiated to the same extent. These results are interpreted to suggest that elevated levels of central nervous system (CNS) hypoxanthine as reported in LNS may affect neuronal development, and to implicate hypoxanthine and abnormal neuronal development as causative factors in the etiology of LNS.

Prolonged contact of the rat superior cervical ganglia (SCG) with the purine a,-methylene-ATP (x,P-Me-ATP) selectively depressed responses to ATP and a,P-Me-ATP but not responses to uridine 5'-triphosphate (UTP), potassium or adenosine. Prolonged contact with the pyrimidine UTP selectively depressed responses to UTP but not responses evoked by a,-Me-ATP, potassium or adenosine. These results are consistent with the presence of P2-purinoceptors and pyrimidinoceptors on the rat SCG and the hypothesis that pyrimidinoceptors exist within the nervous system.

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