Some effects of purines on neurones of guinea-pig superior cervical ganglia

Abstract

1. 1. The actions of adenosine 5′-triphosphate (ATP) and related purine analogues on neurones of isolated superior cervical ganglia in guinea-pig were studied using intracellular recording techniques. 2. 2. Application of ATP (0.1–1 mM) by superfusion evoked a response in half (26 out of 52) of the neurones studied. The response consisted of a slow depolarization (in 23 of the cells) or a hyperpolarization (in 3 cells). The amplitude of depolarization was concentration-dependent and was accompanied by a decrease in input resistance (in 12 of 23 responses). 3. 3. Superfusion of the P 2 x -purinoceptor selective agonist α,β-methylene ATP (1–100 μM), evoked a response in the majority (42 of 58) of neurones studied. The response consisted of a depolarization (in 39 cells) or a hyperpolarization (in 3 cells). The depolarization was also concentration-dependent and was accompanied by a decrease in input resistance (36 of 39 responses). Superfusion of another P 2 x -purinoceptor agonist, β,γ-methylene ATP (10 μm), also produced a small depolarization (5 of 8 cells) which was accompanied by a decrease in input resistance. 4. 4. Application of the P 2 y -purinoceptor selective agonist, 2-methylthio ATP (1–100 μM) evoked a response in approximately half (28 of 55) of the neurones studied. The response consisted of a depolarization (in 23 cells) or a hyperpolarization (in 5 cells). The amplitude of the depolarization was concentration-dependent and accompanied by a decrease in input resistance (13 of 21 responses). 5. 5. Superfusion of the P 1-purinoceptor selective agonist 2-chloroadenosine (100 μM) evoked a response in only a few (3 of 21) of the neurones tested. One cell responded with a depolarization and two cells with a hyperpolarization. However, 2-chloroadenosine at 500 μM elicited a depolarization in 6 out of 8 of the neurones tested. 6. 6. Superfusion of the P 2-purinoceptor antagonist suramin (1 nM–100 μM) elicited a depolarization in all the neurones tested. Reactive blue 2 (1 μM) irreversibly depolarized all cells tested to 0 mV. 7. 7. The potency order of analogues for depolarization was α,β-methylene ATP > β,γ-methylene ATP, 2-methylthio ATP ≥ ATP indicating the involvement of P 2-purinoceptors resembling the P 2 x subtype. P 1-purinoceptors may mediate the hyperpolarization.