Direct coupling through gap junctions is not involved in urethral neurotransmission

Abstract

cells of Cajal (ICC) are believed to participate in urethral neurotransmission and it was proposed that direct coupling of ICC and smooth muscle cells (SMC) through gap junctions (GJ) is involved, although this still remains unclear. Hence, we investigated the distribution of different connexins (Cx 43, Cx40, and Cx37) in the sheep and rat urethra, as well as their possible role in neurotransmission. Conventional PCR confirmed that three Cxs are expressed in the urethra. Moreover, both Cx43 and Cx37-immunoreactivity (-ir) were present in SMC, ICC, and the urothelium, although Cx37-ir was significantly weaker and Cx40-ir was limited to the endothelium. While these results indicate that GJ intercellular communication could occur between SMC and ICC, neither the contractile (noradrenergic) nor the relaxant (nitrergic) responses of the rat and sheep urethra to electrical field stimulation were significantly modified by two different GJ inhibitors: 18␣-glycyrrhetinic acid and a cocktail of Cx mimetic peptides ( Cx43 Gap 26, Cx37, Cx43 Gap 27, and Cx40 Gap 27). By contrast, contractions induced by high K ϩ were effectively reduced by both blockers, evidence that they effectively inhibit intercellular communication. These results indicate that GJ are not implicated in urethral neurotransmission, although the question of whether ICC modulate neurotransmission through some other mechanism remains to be determined.interstitial cells of Cajal; connexin; nitric oxide; norepinephrine URINARY CONTINENCE IS MAINTAINED at rest by a high spontaneous urethral tone, which is augmented by neurally released norepinephrine (NE). This high tone is abruptly lost during micturition by the release of nitric oxide (NO) from the nitrergic nerve network (reviewed in Ref. 1). Several investigations in the last decade led to the suggestion that the neurotransmission processes in the urethra are mediated by interstitial cells of Cajal (ICC) (15, 42, 43), similar to that described in the gastrointestinal tract (3, 5). In the lower urinary tract, it is now accepted the presence of a population of branched noncontractile cells with ultrastructural characteristics similar to those of the gut (41), which are ICC following the nomenclature guidelines approved in the Fifth International Symposium on Interstitial Cells of Cajal, Ireland, 2007. However, studies concerning their role in the urinary tract are scarce. In the urethra, the first description of vimentin-positive cells that accumulated cGMP immunoreactivity upon addition of NO donors, and with a remarkable resemblance to ICC of the intestine, was made by Smet et al. (45). Extensive studies using isolated rabbit ICC revealed the ionic mechanisms that are behind their proposed pacemaker role and these mechanisms are very similar to the activity of ICC seen in the gut (see Ref. 44 for a review). Furthermore, the presence of close contacts between ICC and nitrergic nerves in the urethra from several species has been described (15, 45), suggesting a functional relationship between them. This is ...

Presence of the Ca2+-activated chloride channel anoctamin 1 in the urethra and its role in excitatory neurotransmission

“…ANO1 CHANNELS AND URETHRAL CONTRACTIONS Furthermore, the ICC-Ca 2ϩ oscillator model suggests electrical coupling between ICCs and smooth muscle cells via gap junctions (5). However, this direct coupling appears not to be relevant in urethral neurotransmission despite the existence of gap junctions between these cells, suggesting chemical rather than electrical communication (23). In agreement, the present findings do not support the ICC-Ca 2ϩ oscillator model in whole urethral preparations from sheep, rats, or mice, as no spontaneous or slow wave activity was detected and IP 3 inhibitors had no effect on EFS-induced urethral contractions.…”

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