Involvement of ET_A receptors in the facilitation by endothelin‐1 of non‐adrenergic non‐cholinergic transmission in the rat urinary bladder

Abstract

1 Endothelin-1 (ET-1; 3-10 nM) raised the tone of rat bladders bathed in buffer containing atropine (1 gtM) plus guanethidine (3.4 JAM). In addition, ET-1 potentiated, in a concentration-dependent fashion (1-10 nM), the contractions evoked by both transmural nerve stimulation and applications of exogenous adenosine 5'-triphosphate (ATP). 2 The threshold concentration of ET-1 required to facilitate non-adrenergic non-cholinergic (NANC) transmission and potentiate ATP-induced contractions, was about 10 fold lower than that required to increase the bladder tone (3 nM). 3 The ET-1-induced increase in basal tension reached its maximal effect within 60-90 s. In contrast, the 7.8 JAM ATP-induced contractions increased by 50% within the first minute following incubation with 1O nM ET-1 but required about 5 min to develop the maximal effect. 4 The ET-1-induced potentiation of NANC or ATP responses was long-lasting and persisted in spite of extensive washing. The recovery of the bladder excitability depended on the concentration of ET-1. Following the application of 3 nM ET-1, recovery required 30 min; applications of 10 nM ET-1 required at least 60 min for full recovery. 5The ET-1-induced potentiation of responses was selective for ATP and related structural analogues.ET-1 did not modify the contractions induced by acetylcholine, 5-hydroxytryptamine, prostaglandin F2, or bradykinin. 6 The potency of ET-2 was similar to that of ET-1. ET-3 and ET-C-terminal hexapeptide were inactive up to 100 M. Sarafotoxin S6b was 2 to 3 fold less potent than ET-1 whereas sarafotoxin S6c (100 nM) was inactive. AGETB-9 and AGETB-89, two ETB receptor agonists, were also inactive (up to 100 nM). 7 Removal of one or both disulphide bonds in ET-1 and tryptophan-21 formylation of ET-1, resulted in inactive peptides (up to 100 nM). 8 The ET-1 receptor antagonists, BE-18257B and FR 139317, blocked both the ET-1-induced rise in tone and the potentiation of ATP responses in a concentration-dependent fashion. FR 139317 was at least 30 fold more potent than BE-18257B. Both antagonists blocked at lower concentrations the ET-l increase in bladder tone as compared to the ATP potentiation. The antagonism was slowly reversible. 9 Results are consistent with the presence of ETA receptors in the rat bladder, which mediate both actions of ET-1. The interaction of ET-1 with purinergic mechanisms is discussed.

Pharmacology of the Lower Urinary Tract: Basis for Current and Future Treatments of Urinary Incontinence

“…The main role of ET A receptors in the contractile effects of ETs in the detrusor has been confirmed by several other investigators in animal as well as human bladders (Donoso et al, 1994;Latifpour et al, 1995;Okamoto-Koizumi et al, 1999;Calvert et al, 2002;Yoshida et al, 2003). In human detrusor, OkamotoKoizumi et al (1999), using isometric contraction experiments and RT-PCR, demonstrated that the ET-1-induced contractions were mediated mainly by the ET A receptor and not by the ET B receptor.…”

Detrusor myocyte activity and afferent signaling

“…88 The functional role of ETs in the detrusor has not been established. However, in the rat bladder, Donoso et al 89 found that ET-1 potentiated the contractions evoked by both transmural nerve stimulation (ACh and ATP) and applications of ATP at peptide concentrations 10-fold below those needed to produce an increase in bladder tone. Locally generated ET-1 may thus not only exert a direct contractile effect on the myocyte, but also indirectly increase the effects of other mediators that influence myogenic activity.…”

Endothelin-1 Receptors in Rat Tissues: Characterization by Bosentan, Ambrisentan and CI-1020

“…These results confirmed mainly previous pharmacological observations demonstrating functional significance of ET-1 receptors. [4][5][6][7][8][11][12][13][14]16) …”

“…ET-1 receptors have been shown to be present in several non-vascular tissues such as the heart, kidney and bladder, [3][4][5][6][7][8][9][10] but the receptor properties such as the subtype distribution in these tissues have not been characterized simultaneously. Also, the receptor binding of ET-1 receptor antagonists has not been comparatively examined in different tissues.…”

“…[3][4][5][6][7][8] The biological effects of endothelins are mediated through the specific receptors, ET A and ET B .…”