The biliary epithelium is continuously exposed to highly cytotoxic bile acids and pathogens and thus is at persistent risk for injury. The monolayer mucosal epithelium protects the body from these dangers and once injured. The bile duct repair process essentially involves reconstruction of the bile duct with migrating cells, but there are many questions about the process. It is reported that implantation of a bioabsorbable polymer tube as a bypass graft into the extrahepatic bile duct resulted in bile duct regeneration in the graft site after the artificial duct had been degraded and absorbed. We briefly describe our findings on extrahepatic biliary tissue regeneration with the possibility for clinical applications in mind. The creation of this artificial bile duct may be able to promote the development of the treatment for biliary diseases.
The properties of smooth muscle cell hyperpolarization produced by acetylcholine (ACh) were investigated in mesenteric arteries isolated from mice. The resting membrane potential of the smooth muscle cells was about -60 mV. When ACh (10 μM) was applied for 1 min, the membrane hyperpolarized with a peak amplitude of about 5 mV which was reached in about 1 min, following which the potential slowly reverted to the resting level over about 7 min following withdrawal of ACh from the superfusate (recovery component). Exposure of the artery to 0.5 mM Ba2+, an inhibitor of inward rectifier K-channels, depolarized the membrane by about 13 mV, increased the amplitude of the ACh-induced hyperpolarization to about 10 mV, and facilitated the visualization of the recovery component. Indomethacine (10 μM), an inhibitor of cyclooxygenase, inhibited the recovery component and as a consequence reduced the duration of the hyperpolarization. The ACh-induced response was not markedly altered by either Nω-nitro-L-arginine (10 μM), an inhibitor of nitric oxide (NO) production, or catalase (130 U/ml), a super oxide scavenger. Exogenously applied hydrogen peroxide (H2O2, 300 μM) hyperpolarized the membrane by about 5 mV, which was abolished by catalase. These results suggest that in the mouse mesenteric artery, the ACh-induced hyperpolarization has two components, both an indomethacin-sensitive and an indomethacin-insensitive component. The former component may be produced by prostanoids, while the latter may be produced by factors other than NO or H2O2. The results also suggested that the inward rectifier K-channels may be important for producing the resting membrane potential, but they may not be the main contributor to the ACh-induced hyperpolarization of smooth muscle cell membranes in the mouse mesenteric artery.
The properties of the mechanical responses produced by solutions containing high concentrations of potassium ion (high-K solution, [K+]o = 9-27 mM) were investigated in circular smooth muscle preparations isolated from the rabbit rectum. Isometric recording of mechanical responses of the muscle revealed spontaneous contractions, which successively decreased and finally disappeared in most preparations. Stimulation of the smooth muscle with high-K solutions elicited an increase in both amplitude and frequency of twitch contractions (sustained component), with about a 2 min delay in the beginning (initial inhibition), and a transient large contraction shortly after the cessation of stimulation (after contraction). Transmural nerve stimulation (TNS) with electrical pulses for 1 min at 1 Hz frequency produced a sustained inhibition, but a transient contraction followed after termination of TNS. In the presence of tetrodotoxin (TTX), the TNS-induced responses were abolished, while a high-K solution elicited increased twitch contractions with a short delay and abolished the after contraction. Suramin produced effects similar to TTX on the responses produced by high-K solutions or TNS, but this was not the case for atropine, guanethidine or Nω-nitro-L-arginine (L-NA). Recording membrane potentials with microelectrodes revealed that TNS evoked an inhibitory junction potential (i.j.p.) which was non-adrenergic, non-cholinergic and non-nitrergic in nature. High-K solutions elicited a tri-phasic change in the membrane potential; an initial hyperpolarization, followed by a sustained depolarization and finally a transient depolarization on cessation of high-K stimulation. TTX or suramin inhibited the i.j.p.s and altered the tri-phasic change in the membrane potential produced by a high-K solution to a mono-phasic depolarization. No significant modulation of electrical responses of the membrane induced by TNS or high-K solution was elicited by atropine, guanethidine or L-NA. The results indicated that the circular smooth muscle of the rabbit rectum is innervated by inhibitory nerves, and that stimulation with high-K solutions caused inhibitory neuronal modulation of both electrical and mechanical responses of the smooth muscle, in a suramin-sensitive way.
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