Detrusor specimens were obtained from 5 patients affected by interstitial cystitis (IC) and 5 patients with bladder carcinoma (controls). Muscle strips were prepared for in vitro pharmacological studies. In all detrusor strips taken from IC patients, an important portion of the electrically-induced contraction was atropine-resistant. In contrast, atropine-resistance was never observed in control detrusors. H1 and H2 antagonists did not affect noncholinergic contractile response which, conversely, was abolished following desensitization to alpha, beta methylene ATP (APCPP). Detrusor muscle from patients affected by IC exhibited an increase in sensitivity to APCPP and a decrease in sensitivity to acetylcholine with respect to control detrusor. Taken together these results are consistent with the presence of a purinergic neurotransmission in parasympathetic nerve terminals of the urinary bladder affected by IC, probably as a consequence of alterations in the innervation and/or electrical coupling between smooth muscle cells. The sensitivity of IC detrusor muscle to histamine was much lower than that of control detrusor, suggesting a desensitization of histamine receptors present in the bladder wall of IC patients.

In female Wistar/Rij rats, 10 and 30 mo old, the micturition profiles in conscious animals, the contractile responses of the isolated urinary bladder, and the histology of the vesical tissue have been investigated. During cystomanometry, 60% of conscious senescent rats, but only 25% of young adult rats, showed spontaneous contractions during the bladder-filling phase. In aging rats, micturition pressure and duration of micturition were significantly higher by approximately 40-50%. In contrast, bladder capacity, bladder compliance, micturition volume, and residual volume were not modified with age. In vitro, the contractile responses of the bladder body to KCl, carbachol, arecoline, and alpha,beta-MeATP were similar in tissues from young adult and senescent rats. In contrast, maximum responses to noradrenaline, but not phenylephrine, were two times greater in the older rats. Isoprenaline exhibited the same potency in relaxing KCl-precontracted bladder body of 10- and 30-mo-old animals. Morphometric analysis showed a significant increase in the mean thickness of the muscularis layer with age, whereas the collagen density significantly decreased in the muscularis and in the lamina propria layers. The fact that the majority of senescent rats displayed bladder instability and increased response to alpha-adrenergic agonists suggests that this strain of rat seems a good model for the aged human. However, other characteristics of the aging human urinary tract (urinary frequency, decreased cystometric capacity, and decreased detrusor contractility associated with fibrosis) are not present.

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Non-voiding activity is sensitive to muscarinergic antagonists and β(3)-adrenoceptor agonists, but there are clear differences between the two drugs. A model is proposed to account for these observations where both agents act on a 'pacemaker-like' mechanism with cholinergic excitatory and adrenergic inhibitory inputs. Such concepts may provide insights into the nature of overactive bladder and the site of action of key therapeutic drugs.

Background and purpose: Venoms are a rich source of ligands for ion channels, but very little is known about their capacity to modulate G-protein coupled receptor (GPCR) activity. We developed a strategy to identify novel toxins targeting GPCRs. Experimental approach: We studied the interactions of mamba venom fractions with a1-adrenoceptors in binding experiments with 3 H-prazosin. The active peptide (AdTx1) was sequenced by Edman degradation and mass spectrometry fragmentation. Its synthetic homologue was pharmacologically characterized by binding experiments using cloned receptors and by functional experiments on rabbit isolated prostatic smooth muscle. Key results: AdTx1, a 65 amino-acid peptide stabilized by four disulphide bridges, belongs to the three-finger-fold peptide family. It has subnanomolar affinity (Ki = 0.35 nM) and high specificity for the human a1A-adrenoceptor subtype. We showed high selectivity and affinity (Kd = 0.6 nM) of radio-labelled AdTx1 in direct binding experiments and revealed a slow association constant (kon = 6 ¥ 10) with an unusually stable a1A-adrenoceptor/AdTx1 complex (t1/2diss = 3.6 h). AdTx1 displayed potent insurmountable antagonism of phenylephrine's actions in vitro (rabbit isolated prostatic muscle) at concentrations of 10 to 100 nM. Conclusions and implications:AdTx1 is the most specific and selective peptide inhibitor for the a1A-adrenoceptor identified to date. It displays insurmountable antagonism, acting as a potent relaxant of smooth muscle. Its peptidic nature can be exploited to develop new tools, as a radio-labelled-AdTx1 or a fluoro-labelled-AdTx1. Identification of AdTx1 thus offers new perspectives for developing new drugs for treating benign prostatic hyperplasia.