Figure 2.

(A) Left-hand side: responses of the guinea pig taenia coli to NANC nerve stimulation (NS, 1 Hz, 0.5 ms pulse duration, for 10 s at supramaximal voltage) mimicked by ATP (2 × 10⁻⁶ M). The responses consist of a relaxation, followed by a ‘rebound contraction’. Atropine (1.5 × 10⁻⁷ M), guanethidine (5 × 10⁻⁶ M) and sodium nitrite (7.2 × 10⁻⁴ M) were present. [From Burnstock and Wong (1978), reproduced with kind permission of the Nature Publishing Group.] Right-hand side: a comparison of the NANC contractile responses of the guinea pig bladder strip to intramural nerve stimulation (NS: 5 Hz, 0.2 ms pulse duration and supramaximal voltage) mimicked by exogenous ATP (8.5 µM). Atropine (1.4 µM) and guanethidine (3.4 µM) were present throughout. [From Burnstock et al. (1978), reproduced with kind permission of the Nature Publishing Group.] (B) Effect of changing the calcium ion (Ca²⁺) concentration on the release of ATP (measured with the firefly luciferin/luciferase technique) from the guinea pig isolated bladder strip during stimulation of NANC nerves. Upper trace: mechanical recording of changes in tension (g) during intramural nerve stimulation (NS: 20 Hz, 0.2 ms pulse duration, supramaximal voltage for 20 s). Lower trace: concentration of ATP in consecutive 20 s fractions of the superfusate. The Ca²⁺ concentration in the superfusate varied as follows: (i) 2.5 mM (normal Krebs); (ii) 0.5 mM; (iii) 0.25 mM; and (iv) 2.5 mM. The successive contractions were separated by 60 min intervals as indicated by the breaks in the mechanical trace. Atropine (1.4 µM) and guanethidine (3.4 µM) were present throughout. [From Burnstock et al. (1978), reproduced with kind permission of the Nature Publishing Group.] (C) The effect of α,β-methylene ATP (α,β-meATP) receptor desensitization on the responses to nerve stimulation (↑), ATP (▵) and histamine (Hist). Atropine (1 µM) and guanethidine (3.4 µM) were present throughout. (Top panel) Control responses. (Middle panel) α,β-meATP desensitization, reached by five successive applications (▴) at approximately 4 min intervals, completely abolished nerve-mediated (↑) and ATP-induced (▵) responses. However, histamine-induced contraction is only slightly reduced. (Bottom panel) Responses 60 min after washing with Krebs. [Reproduced from Kasakov and Burnstock (1983), with permission.]