Inhalation anaesthetic isoflurane inhibits the muscarinic cation current and carbachol-induced gastrointestinal smooth muscle contractions

Abstract

Gastrointestinal tract motility may be demoted significantly after surgery operations at least in part due to anaesthetic agents, but there is no comprehensive explanation of the molecular mechanism(s) of such adverse effects. Anesthetics are known to interact with various receptors and ion channels including several subtypes of transient receptor potential (TRP) channels. Two members of the canonical subfamily of TRP channels (TRPC), TRPC4 and TRPC6 are Ca2+-permeable cation channels involved in visceral smooth muscle contractility induced by acetylcholine, the primary excitatory neurotransmitter in the gut. In the present study, we aimed to study the effect of anesthetics on muscarinic receptor-mediated excitation and contraction of intestinal smooth muscle. Here we show that muscarinic cation current (mICAT) mediated by TRPC4 and TRPC6 channels in mouse ileal myocytes was strongly inhibited by isoflurane (0.5mM), one of the most commonly used inhalation anaesthetics. Carbachol-activated mICAT was reduced by 63 ± 11% (n=5), while GTPγS-induced (to bypass muscarinic receptors) current was inhibited by 44 ± 9% (n=6). Furthermore, carbachol-induced ileum and colon contractions were inhibited by isoflurane by about 30%. We discuss the main sites of isoflurane action, which appear to be G-proteins and muscarinic receptors, rather than TRPC4/6 channels. These results contribute to our better understanding of the signalling pathways affected by inhalation anaesthetics, which may cause ileus, and thus may be important for the development of novel treatment strategies during postoperative recovery.

Suppression of mICAT in Mouse Small Intestinal Myocytes by General Anaesthetic Ketamine and its Recovery by TRPC4 Agonist (-)-englerin A

“…Overall, ketamine induced inhibition of mI CAT is highly reminiscent of the effects of isoflurane (Dryn et al, 2018). To our knowledge, our experiments provide first indication that G-proteins can be inhibited by ketamine, but obviously much further work is required to clarify the underlying mechanism.…”

“…The ileum longitudinal smooth muscle (SM) layer was rapidly removed by carefully peeling the SM in the longitudinal direction and placed into a normal physiological salt solution (PSS) containing (in mM): NaCl 120, glucose 12, HEPES 10, KCl 6, CaCl 2 2.5, MgCl 2 1.2, pH 7.4 (adjusted with NaOH). SM cells were isolated by enzymatic digestion using (in mg/ml) 1 collagenase type 1A, 1 soybean trypsin inhibitor II-S, 1.5 bovine serum albumin in divalent cation-free PSS following tissue incubated for 18 min at 36.5°C, as described in more detail elsewhere (Dryn et al, 2018).…”

“…SM preparations and cells were randomly assigned to various tests and data analysis was performed independently in a semiblinded manner whenever possible (it should be noted that the inhibitory effects of ketamine were fairly obvious to the operator even without data analysis). Group size was determined based on our previous extensive experience studying mI CAT , and in particular on our recent similar study of mI CAT inhibition produced by isoflurane (Dryn et al, 2018). Current amplitudes were normalized by cell capacitance to account for variations in cell size.…”

Transient Receptor Potential Canonical (TRPC) Channels: Then and Now

“…Tsvilovskyy et al concluded that TRPC4 and TRPC6 channel activation are critical for stimulating the muscarinic cation current (mICAT) in intestinal smooth muscle [ 255 , 256 ], indicating that the mICAT may consist of TRPC4 and TRPC6 and that their activation may be important for accelerating intestinal motility. It has been reported that the inhibitory effect of anesthetic agents, such as isoflurane, decreasing gastrointestinal tract motility is mediated by inhibiting the G-protein signaling that is important for stimulation of mICAT formed by TRPC4 and TRPC6 channels [ 257 ]. However, the reports on the function of TRPCs in the gastrointestinal tract are scarce and new investigations are needed to better understand their contribution to regulating gut function.…”

Gastrointestinal motility modulation by stress is associated with reduced smooth muscle contraction through specific transient receptor potential channel

“…Activated receptors result in the contraction of gastrointestinal smooth muscles via Ca 2+ influx. There are reports that the activated muscarinic receptor opens non-selective cation channels which depolarizes the membrane in guinea-pig jejunal smooth muscles [ 33 ], that TRPC4 and TRPC6 are involved in visceral smooth muscle contractility induced by ACh [ 10 , 15 ], and that TRPC3/C6/C7 are involved in Ca 2+ currents mediated by muscarinic receptor [ 19 ]. In the stressed ileum, in contrast, the second half of the EFS-induced contraction was suppressed by 80% under atropine-treated conditions.…”