Frequency dependence of excitation–contraction of multicellular smooth muscle preparations: the relevance to bipolar electrosurgery

Contribution of transient receptor potential vanilloid 1 (TRPV1) channel to cholinergic contraction of rat bladder smooth muscle

Transient receptor potential vanilloid 1 (TRPV1) is a calcium-permeable ion channel that is gated by the pungent constituent of red chili pepper, capsaicin, and by related chemicals from the group of vanilloids, in addition to noxious heat. It is expressed mostly in sensory neurons to act as a detector of painful stimuli produced by pungent chemicals and high temperatures. Although TRPV1 is also found outside the sensory nervous system, its expression and function in the bladder detrusor smooth muscle (DSM) remain controversial. Here, by using Ca2+ imaging and patch clamp on isolated rat DSM cells, in addition to tensiometry on multicellular DSM strips, we show that TRPV1 is expressed functionally in only a fraction of DSM cells, in which it acts as an endoplasmic reticulum Ca2+-release channel responsible for the capsaicin-activated [Ca2+]i rise. Carbachol-stimulated contractions of multicellular DSM strips contain a TRPV1-dependent component, which is negligible in the circular DSM but reaches ≤50% in the longitudinal DSM. Activation of TRPV1 in rat DSM during muscarinic cholinergic stimulation is ensured by phospholipase A2-catalysed derivation of arachidonic acid and its conversion by lipoxygenases to eicosanoids, which act as endogenous TRPV1 agonists. Immunofluorescence detection of TRPV1 protein in bladder sections and isolated DSM cells confirmed both its preferential expression in the longitudinal DSM sublayer and its targeting to the endoplasmic reticulum. We conclude that TRPV1 is an essential contributor to the cholinergic contraction of bladder longitudinal DSM, which might be important for producing spatial and/or temporal anisotropy of bladder wall deformation in different regions during parasympathetic stimulation. KEY POINTS: The transient receptor potential vanilloid 1 (TRPV1) heat/capsaicin receptor/channel is localized in the endoplasmic reticulum membrane of detrusor smooth muscle (DSM) cells of the rat bladder, operating as a calcium-release channel. Isolated DSM cells are separated into two nearly equal groups, within which the cells either show or do not show TRPV1-dependent [Ca2+]i rise. Carbachol-stimulated, muscarinic ACh receptor-mediated contractions of multicellular DSM strips contain a TRPV1-dependent component. This component is negligible in the circular DSM but reaches ≤50% in longitudinal DSM. Activation of TRPV1 in rat DSM during cholinergic stimulation involves phospholipase A2-catalysed derivation of arachidonic acid and its conversion by lipoxygenases to eicosanoids, which act as endogenous TRPV1 agonists.

An ex vivo preliminary investigation into the impact of parameters on tissue welding strength in small intestine mucosa-mucosa end-to-end anastomosis

Background: Tissue welding is an electrosurgical technique that can fuse tissue for small intestine anastomosis. However, limited knowledge exists on its application in mucosa-mucosa end-to-end anastomosis. This study investigates the effects of initial compression pressure, out-put power, and duration time on anastomosis strength ex vivo in mucosa-mucosa end-to-end anastomosis. Methods: Ex vivo porcine bowel segments were used to create 140 mucosa-mucosa end-to-end fusions. Different experimental parameters were employed for fusion, including initial com-pression pressure (50kPa-400 kPa), output power (90W, 110W, and 140W), and fusion time (5, 10, 15, 20 s). The fusion quality was measured by burst pressure and optical microscopes. Results: The best fusion quality was achieved with an initial compressive pressure between 200 and 250 kPa, an output power of 140W, and a fusion time of 15 s. However, an increase in output power and duration time resulted in a wider range of thermal damage. There was no significant difference between the burst pressure at 15 and 20 s (p > 0.05). However, a substantial increase in thermal damage was observed with longer fusion times of 15 and 20 s (p < 0.05). Conclusion: The best fusion quality for mucosa-mucosa end-to-end anastomosis ex vivo is achieved when the initial compressive pressure is between 200 and 250 kPa, the output power is approximately 140W, and the fusion time is approximately 15 s. These findings can serve as a valuable theoretical foundation and technical guidance for conducting animal experiments in vivo and subsequent tissue regeneration.

Temperature-dependent contractility of rat tunica dartos muscle: contribution of cold, menthol-sensitive TRPM8

Tunica dartos smooth muscle (TDSM) lies beneath the scrotal skin, and its contraction leads to scrotum wrinkling upon cooling. However, neither the nature of TDSM cold-sensitivity nor the underlying molecular sensors are well understood. Here we have investigated the role of cold/menthol-sensitive TRPM8 channel in TDSM temperature-dependent contractility. The contraction of isolated male rat TDSM strips was studied by tensiometry. TRPM8 expression was assayed by RT-PCR and fluorescence immunochemistry. Isolated TDSM strips responded to cooling from 33 °C to 20 °C by enhancement of basal tension, and increase of the amplitude and duration of electric field stimulated (EFS) contractions. The effects of cold on basal tension, but not on EFS-contractions, could be 80% inhibited by TRPM8 blockers, capsazepine and BCTC [N-(4‑tert-butylphenyl)-4-(3-chloropyridin-2-yl)piperazine-1-carboxamide], and could be partially mimicked by menthol. RT-PCR and immunolabeling showed TRPM8 mRNA and protein expression in TDSM cells with protein labelling being predominantly localized to intracellular compartments. Chemical castration of male rats consequent to the treatment with androgen receptor blocker, flutamide, led to the abrogation of cold effects on TDSM basal tension, but not on EFS-contractions, and to the disappearance of TRPM8 protein expression. We conclude that TRPM8 is involved in the maintenance of basal cold-induced TDSM tonus, but not in sympathetic nerve-mediated contractility, by acting as endoplasmic reticulum Ca²⁺ release channel whose expression in TDSM cells requires the presence of a functional androgen receptor. Thus, TRPM8 plays a crucial role in scrotal thermoregulation which is important for maintaining normal spermatogenesis and male fertility.

Alterations in detrusor contractility in rat model of bladder cancer

Urinary incontinence of idiopathic nature is a common complication of bladder cancer, yet, the mechanisms underlying changes in bladder contractility associated with cancer are not known. Here by using tensiometry on detrusor smooth muscle (DSM) strips from normal rats and rats with bladder cancer induced by known urothelial carcinogen, N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN), we show that bladder cancer is associated with considerable changes in DSM contractility. These changes include: (1) decrease in the amplitude and frequency of spontaneous contractions, consistent with the decline of luminal pressures during filling, and detrusor underactivity; (2) diminution of parasympathetic DSM stimulation mainly at the expense of m-cholinergic excitatory transmission, suggestive of difficulty in bladder emptying and weakening of urine stream; (3) strengthening of TRPV1-dependent afferent limb of micturition reflex and TRPV1-mediated local contractility, promoting urge incontinence; (4) attenuation of stretch-dependent, TRPV4-mediated spontaneous contractility leading to overflow incontinence. These changes are consistent with the symptomatic of bladder dysfunction in bladder cancer patients. Considering that BBN-induced urothelial lesions in rodents largely resemble human urothelial lesions at least in their morphology, our studies establish for the first time underlying reasons for bladder dysfunction in bladder cancer.

Energy-Based Tissue Fusion for Sutureless Closure: Applications, Mechanisms, and Potential for Functional Recovery

As minimally invasive surgical techniques progress, the demand for efficient, reliable methods for vascular ligation and tissue closure becomes pronounced. The surgical advantages of energy-based vessel sealing exceed those of traditional, compression-based ligatures in procedures sensitive to duration, foreign bodies, and recovery time alike. Although the use of energy-based devices to seal or transect vasculature and connective tissue bundles is widespread, the breadth of heating strategies and energy dosimetry used across devices underscores an uncertainty as to the molecular nature of the sealing mechanism and induced tissue effect. Furthermore, energy-based techniques exhibit promise for the closure and functional repair of soft and connective tissues in the nervous, enteral, and dermal tissue domains. A constitutive theory of molecular bonding forces that arise in response to supraphysiological temperatures is required in order to optimize and progress the use of energy-based tissue fusion. While rapid tissue bonding has been suggested to arise from dehydration, dipole interactions, molecular cross-links, or the coagulation of cellular proteins, long-term functional tissue repair across fusion boundaries requires that the reaction to thermal damage be tailored to catalyze the onset of biological healing and remodeling. In this review, we compile and contrast findings from published thermal fusion research in an effort to encourage a molecular approach to characterization of the prevalent and promising energy-based tissue bond.

Impairment of cholinergic bladder contractility in rat model of type I diabetes complicated by cystitis: Contribution of neurotransmitter-degrading ectoenzymes

Parasympathetic regulation of urinary bladder contractions primarily involves acetylcholine release and activation of detrusor smooth muscle (DSM) muscarinic acetylcholine (mACh) receptors. Co-release of ATP and activation of DSM purinergic P2X1-receptors may participate as well in some species. Both types of neuromuscular transmission (NMT) are impaired in diabetes, however, which factors may contribute to such impairment remains poorly understood. Here by using rats with streptozotocin(STZ)-induced type I diabetes (8th week after induction) we show that contribution of atropine-sensitive m-cholinergic component to the contractions of urothelium-denuded DSM strips evoked by electric field stimulation (EFS) greatly increased when diabetic bladders presented overt signs of accompanying cystitis. Modeling of hemorrhagic cystitis alone in control rats by cyclophosphamide injection only modestly increased m-cholinergic component of EFS-contractions. However, exposure of DSM strips from control animals to acetylcholinesterase (AChE) inhibitor, neostigmine (1-10 μM) largely reproduced alterations in EFS contractions observed in diabetic DSM complicated by cystitis. Ellman's assay revealed statistically significant 31% decrease of AChE activities in diabetic vs. control DSM. Changes in purinergic contractility of diabetic DSM were consistent with altered P2X1-receptor desensitization and re-sensitization. They could be mimicked by pharmacological inhibition of ATP-degrading ecto-ATPases with ARL 67156 (50 μM), pointing to compromised extracellular ATP clearance as underlying reason. We conclude that decreased AChE activities associated with diabetes and likely cystitis provide complementary factor to the described in literature altered expression of mACh receptor subtypes linked to diabetes as well as to cystitis to produce dramatic modification of cholinergic NMT.

TRPA1-dependent regulation of bladder detrusor smooth muscle contractility in normal and type I diabetic rats

TRPA1 is a Ca²⁺-permeable cation channel that is activated by painful low temperatures (˂17 °C), irritating chemicals, reactive metabolites and mediators of inflammation. In the bladder TRPA1 is predominantly expressed in sensory afferent nerve endings, where it mediates sensory transduction. The contractile effect of its activation on detrusor smooth muscle (DSM) is explained by the release from sensory afferents of inflammatory factors – tachykinins and prostaglandins, which cause smooth muscle cell contraction. Diabetes is a systemic disease, with common complications being diabetic cystopathies and urinary incontinence. However, data on how diabetes affects bladder contractility associated with TRPA1 activation are not available. In this study, by using a rat model with streptozotocin-induced type I diabetes, contractility measurements of DSM strips in response to TRPA1-activating and modulating pharmacological agents and assessment of TRPA1 mRNA expression in bladder-innervating dorsal root ganglia, we have shown that diabetes enhances the TRPA1-dependent mechanism involved in bladder DSM contractility. This is not due to changes in TRPA1 expression, but mainly due to the general inflammatory reaction caused by diabetes. The latter leads to an increase in cyclooxygenase-2-dependent prostaglandin synthesis through the mechanisms associated with substance P activity. This results in the enhanced functional coupling between the tachykinin and prostanoid systems, and the concomitant increase of their impact on DSM contractility in response to TRPA1 activation.

Myorelaxant action of fluorine-containing pinacidil analog, flocalin, in bladder smooth muscle is mediated by inhibition of L-type calcium channels rather than activation of KATP channels

Flocalin (FLO) is a new ATP-sensitive K(+) (KATP) channel opener (KCO) derived from pinacidil (PIN) by adding fluorine group to the drug's structure. FLO acts as a potent cardioprotector against ischemia-reperfusion damage in isolated heart and whole animal models primarily via activating cardiac-specific Kir6.2/SUR2A KATP channels. Given that FLO also confers relaxation on several types of smooth muscles and can partially inhibit L-type Ca(2+) channels, in this study, we asked what is the mechanism of FLO action in bladder detrusor smooth muscle (DSM). The actions of FLO and PIN on contractility of rat and guinea pig DSM strips and membrane currents of isolated DSM cells were compared by tensiometry and patch clamp. Kir6 and SUR subunit expression in rat DSM was assayed by reverse transcription PCR (RT-PCR). In contrast to PIN (10 μM), FLO (10 μM) did not produce glibenclamide-sensitive DSM strips' relaxation and inhibition of spontaneous and electrically evoked contractions. However, FLO, but not PIN, inhibited contractions evoked by high K(+) depolarization. FLO (40 μM) did not change the level of isolated DSM cell's background K(+) current, but suppressed by 20 % L-type Ca(2+) current. Determining various Kir6 and SUR messenger RNA (mRNA) expressions in rat DSM by RT-PCR indicated that dominant KATP channel in rat DSM is of vascular type involving association of Kir6.1 and SUR2B subunits. Myorelaxant effects of FLO in bladder DSM are explained by partial blockade of L-type Ca(2+) channel-mediated Ca(2+) influx rather than by hyperpolarization associated with increased K(+) permeability. Thus, insertion of fluorine group in PIN's structure made the drug more discriminative between Kir6.2/SUR2A cardiac- and Kir6.1/SUR2B vascular-type KATP channels and rendered it partial L-type Ca(2+) channel-blocking potency.

Comparison of a New High-Frequency Electric Welding System for Intestinal Closure with Hand-Sewn In Vivo Pig Model

BACKGROUND

Various surgical small intestinal anastomosis methods are in current use, but improvements are always desired. Thus, we compared the feasibility, effectiveness, and safety of a new high-frequency electric welding (HFEW) system for sealing the small bowel versus a hand-sewn in vivo pig model.

MATERIALS AND METHODS

The 96 bowel segments of three pigs were randomized to be sutured either by the HFEW-300 PATONMED device (E.O. Paton Electric Welding Institute of the National Academy of Sciences of Ukraine, Kiev, Ukraine) or hand-sewn, and mucosa-to-mucosa fusions were subjected in vivo testing in the pigs. Bursting pressures, suture time, thermal damage, and the temperature of sealed ends were measured.

RESULTS

Segments that had been treated with a hand-sutured ligature or double-sealed with HFEW were compared. Burst pressure was significantly higher in the hand-sutured group than in the HFEW group (136.2 mm Hg versus 75.8 mm Hg, P<.01). All 48 pig small bowels closed by the HFEW-300 generator showed a success rate of 100.0%. The closing time in the HFEW group was significantly shorter (P<.01). The pathological changes of the closed ends were mainly presented as acute thermal- and pressure-induced injuries.

CONCLUSIONS

Outcomes of the current in vivo study suggest that HFEW is an effective and safe method for ligation of the small bowel in pigs.