Non-adrenergic non-cholinergic excitatory innervation of the guinea-pig isolated renal pelvis: involvement of capsaicin-sensitive primary afferent neurons.

Circular muscle strips from the guinea-pig renal pelvis exhibit a spontaneous activity averaging about 50% of maximal contractile response at a frequency of about six contractions/min. This spontaneous activity is tetrodotoxin resistant. Acetylcholine and noradrenaline (one to 100 microM) produce a positive inotropic effect which was abolished or strongly inhibited by atropine and phentolamine, respectively. Electrical field stimulation (five to 10 Hz, 0.5 ms pulse width for 10 s, 60 V, maximal voltage) produces a transient positive inotropic response which is tetrodotoxin-sensitive but unaffected by atropine and phentolamine alone or in combination, as well as by atropine plus guanethidine. Application of capsaicin produced a large positive inotropic response which was not reproduced upon a second application of the drug (desensitization). After in vitro capsaicin desensitization, the response to electrical field stimulation was abolished, indicating its dependence on activation of peripheral endings of sensory nerves. These findings demonstrate the existence of a non-adrenergic non-cholinergic functional innervation of the guinea-pig renal pelvis which is entirely dependent on sensory nerve activation.