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

¹ Department of Physiology, Dartmouth Medical School, Hanover, New Hampshire

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.

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