Excitation of rat urinary bladder by coaxial electrodes and by chemical agents

Abstract

Electrical stimulation of an isolated rat urinary bladder in tris buffered Ringer's solution by coaxial electrodes elicits contractile responses amounting to 70–130 cm of water pressure. If the Ringer's solution is replaced by isotonic K2SO4 solution, pressures of 60–110 cm water pressure are developed. Responses elicited by low stimulating frequencies (.5–2.5/sec) and by K2SO4 are potentiated by physostigmine, however, 2 mg/liter atropine throughout the entire frequency range of .5–10/sec is without effect. The stimulating actions of K2SO4 and electrical stimuli are dependent upon the availability of Ca++. Responses to electric stimuli are believed to be mediated by way of cholinergic neural elements, those from K+ by a depolarization of the muscle fibers. To a more limited extent the contractile responses resulting from acetylcholine (ACh) are dependent upon Ca++ and contractures are also produced by ACh in bladders suspended in isotonic K2SO4. Conversely, electrical pulses or K2SO4 are effective stimuli in the presence of quantities of ACh or carbamylcholine sufficient to produce maximal responses. This suggests a different site of action for exogenous ACh as opposed to endogenous mediator released from cholinergic motor nerve terminals during motor nerve stimulation.