Release of acetylcholine from isolated canine renal tissue

Slices of canine kidney were incubated with [3H]choline and Ringer-Krebs solution for 30 min. Secretion of [3H]acetylcholine ([3H]ACh) was evoked by either 1) an electrical field stimulation (0.5-1 Hz, 2 ms, 20 V) or 2) high-potassium (57 mM) superfusion for 3 min to depolarize nerve terminals. With these stimulatory schedules, the 3H release mainly consists of [3H]-ACh. The ACh release is Ca2+ dependent and blocked in presence of a Mg2(+)-rich medium. Thus suppression of ongoing neuronal activity by tetrodotoxin and blockade of nicotinic receptors by hexamethonium reduced the electrically evoked ACh release. With both stimulatory procedures, the secretory response was modified by pilocarpine and atropine. In addition, the release of [3H]ACh produced by electrical field stimulation was inhibited by neostigmine, indicating the presence of functional presynaptic receptors in cholinergic putative terminals. Activation of these receptors depresses ACh secretion. The disruption of extrinsic renal nerves 7 days before did not diminish [3H]ACh release caused by K+ stimulation and, conversely, increased [3H]ACh released by electrical field stimulation. These data support the presumed existence of cholinergic nerve terminals in the canine kidney that can release ACh under suitable conditions of stimulation.