Electrical and Mechanical Activity of the Isolated Lower Urinary Tract of the Guinea‐pig

Abstract

1 Strips of urethra taken from guinea-pigs contracted in response to acetylcholine, noradrenaline (via a-adrenoceptors) and 5-hydroxytryptamine, and were relaxed by adenosine triphosphate (ATP) if the tone was raised. Isoprenaline produced relaxation of bladder strips (via Padrenoceptors) whereas ATP caused contraction. 2 Atropine completely blocked all responses to acetylcholine; quinidine failed to block ATP responses selectively; methysergide blocked responses of the urethra but not the bladder to 5-hydroxytryptamine. 3 Spontaneous electrical activity was recorded with intracellular microelectrodes from all regions: in the urethra infrequent bursts of spikes occurred at 1-7 min intervals; regular spikes at 6-30/min were recorded from the detrusor muscle. In the bladder base, bursts of spikes were superimposed on the regular pattern. 4 Bursts of spikes in the urethra were initiated by noradrenaline, phenylephrine or acetylcholine and inhibited by ATP; regular spikes in the bladder were accelerated by acetylcholine or ATP and slowed by noradrenaline or isoprenaline. 5 The intrinsic electrical activity and pharmacological properties of the urethra therefore differ from those of the bladder. This may account for the different responses of the two regions in normal function.

Influence of 5‐hydroxytryptamine and the effect of a new serotonin receptor antagonist (sarpogrelate) on detrusor smooth muscle of streptozotocin‐induced diabetes mellitus in the rat *

“…Previous studies have documented the ability of serotonin to contract strips of urinary bladder obtained from dogs, 7,8 cats, 9 rabbits, 10 guinea pigs, 11 and humans. 12 We found that the contractile response to 5-HT was slightly but not significantly reduced in the rat bladder.…”

Purinergic signalling in the urinary tract in health and disease

“…A more recent paper has claimed that the excitatory effect of ATP on rabbit urethral smooth muscle is mediated by activation of P2Y receptors on ICCs, which act as pacemakers [85]. Bursts of spikes in the urethra were initiated by NA or ACh, but inhibited by ATP [124], perhaps after breaking down to adenosine. In the pre-contracted proximal urethra of the hamster, NANC nerve stimulation and exogenous ATP were also shown to produce relaxations, which were attenuated by suramin and Reactive Blue 2, and to a lesser extent by 8-PT, but not by PPADS.…”

“…It is interesting that ATP has been claimed to be an inhibitory neurotransmitter to the guinea-pig urinary bladder neck [294]. When the tone of the urethra is raised, ATP caused relaxation, but if the tone of the urethra is low, high concentrations of ATP can cause contraction [124,169,351,553]. A more recent paper has claimed that the excitatory effect of ATP on rabbit urethral smooth muscle is mediated by activation of P2Y receptors on ICCs, which act as pacemakers [85].…”

“…However, a small component of purinergic neurotransmission may also be involved [24,561,563]. ATP has been shown to cause urethral relaxation, perhaps via P2Y 1 receptors, in pigs [719], guinea-pigs [124], rabbits [533] and hamsters [559]. It is interesting that ATP has been claimed to be an inhibitory neurotransmitter to the guinea-pig urinary bladder neck [294].…”

The physiological function of lower urinary tract smooth muscle

“…Electrical activity occurs in bursts of APs superimposed on a slower rhythmic oscillation of membrane potential, and can be initiated by autonomic transmitters (Callahan and Creed, 1981). Both L-type and T-type Ca 2+ -currents have been recorded in isolated myocytes.…”