A. V. Romanenko

Effect of thiamine on neuromuscular transmission in smooth muscles

Effects of thiamine, thiamine monophosphate (TMP), and thiamine diphosphate (TDP) on excitatory cholinergic and inhibitory noncholinergic nonadrenergic neuromuscular transmissions were studied in the smooth muscles of the gastric fundus and in the circular layer of the distal colon of the guinea pig, respectively. It was found that, when applied in the physiological concentration range, thiamine, TMP, and TDP evoked depolarization and an increase in strain in the smooth muscle strips, as well as an increase in the amplitude of inhibitory synaptic potentials and postinhibitory depolarization. The amplitude of the excitatory synaptic potentials increases in the presence of thiamine and TMP, and decreases in the presence of TDP. The results obtained suggest that thiamine and TMP, which are normally present in the extracellular medium, may modulate synaptic transmission, as well as the electrical and contractile activity of the smooth muscles in the gastrointestinal tract.

Synaptic inhibition of smooth muscles of the human colon: Effects of vitamin B6 and its derivatives

Spontaneous activity, which is manifested as slow depolarization waves and action potentials, is observed in most (81%) smooth muscles (SMs) of the circular layer of the human colon. Independently of the type of pathology, inhibitory junction potentials (IJPs) in SMs of various parts of the human colon are evoked by intramural stimulation; ranges of parameters of these potentials were comparable with those observed in muscle intestinal fragments isolated at a distance of several tens of centimeters from the zone of injury. In muscle strips (MSs) of such fragments, pyridoxal-5′-phosphate (PPh) applied in different concentrations caused suppression of IJPs: in the concentration of 1·10−8 to 1·10−4 M it decreased the amplitude, and in the concentrations of 1·10−5 to 1·10−4 M and 1·10−4 M, respectively, it decreased rates of the half-amplitude rise and decay of these potentials. Pyridoxal (1·10−4 M) and 4-pyridoxolic acid (1·10−4 M) also caused a drop in the amplitude of IJPs; however, these agents influenced this parameter to a lesser extent, as compared with the effect of 1·10−4 M PPh. Pyridoxine (1·10−4 M) and pyridoxamine (1·10−4 M) evoked no significant changes in the parameters of IJPs in MSs of the human colon. Our data allow us to hypothesize that the suppressing effect of PPh on IJPs is determined by the presence of a purinergic component present in non-adrenergic inhibition of SMs of the human colon.

Pre- and post-synaptic modulation of neuromuscular transmission in smooth muscles by thiazole analogs of vitamin B1

The effects of structural analogs of vitamin B1, thiazole derivatives with alkyloxycarbonylmethyl substituents at position 3, on neuromuscular transmission were studied in the smooth muscles of the guinea pig gastrointestinal tract. In the smooth muscles of the stomach, the studied compounds depressed excitatory cholinergic neuromuscular transmission. In the case of 3-hexyl-, 3-decyl-, and 3-dodecyloxycarbonylmethyl-4-methyl-5-(2-hydroxyethyl)-thiazole chlorides this effect was due to their presynaptic action, while in the case of 3-menthyloxycarbonylmethyl-4-methyl-5-(2-hydroxyethyl)thiazole chloride it was due to the block of muscarinic acetylcholine receptors in smooth muscle fibers. In the circular smooth muscles of the distal colon, 3-decyloxycarbonylmethyl-4-methyl-5-(2-hydroxyethyl)thiazole chloride blocked non-adrenergic inhibitory synaptic potentials (ISP) apparently through interaction with the ATP-sensitive acetylcholine receptors. In contrast, 3-hexyloxycarbonylmethyl-4-methyl-5-(2-hydroxyethyl)thlazole chloride enhanced postinhibitory excitation, without changing the ISP amplitude. Possible ways of pre- and post-synaptic modulations of neuromuscular transmission by thiazole derivatives are discussed. It has been suggested that the effects of these compounds are due to similarity of their structures to the structure of vitamin B1.

Effects of thiazole analogs of vitamin B1 on neuromuscular transmission and α-latrotoxin-induced transmitter release in skeletal muscles

Thiazole analogs of vitamin B1 3-decyloxycarbonylmethyl-4-methyl-5-(2-hydroxyethyl)thiazole chloride (DMHT) and 3-decyloxycarbonylmethyl-4-methylthiazole chloride (DMT) suppress quantum transmitter release from nerve terminals in the frog skeletal muscle. Intraperitoneal administration of these compounds to mice suppresses behavioral motor activity, diminishes motor coordination, and suppresses the corazol-induced seizures. Application of DMHT reduces the α-latrotoxin-induced massive transmitter release from nerve terminals in the frog skeletal muscle and suppresses latrotoxin-induced seizures in mice. In model experiments, DMHT blocks Ca2+ entry through the ion channels formed by α-latrotoxin in a bilayer lipid membrane. It has been suggested that the effectiveness of DMHT and DMT is determined by the presence of a thiazole cycle in their molecules that, among all endogenous biologically active compounds, is possessed only by vitamin B1 and its metabolites.

Effect of B1 hypovitaminosis on the efficacy of neuromuscular transmission in the murine diaphragm

In mice kept on a diet with no vitamin B1, the total content of thiamine in the brain decreased, and muscle contractions evoked by stimulation of the nerve in phrenico-diaphragmatic preparations obtained from such animals became weaker. The measurements were performed in Krebs solution with a decreased content of Ca2+ and increased concentration of Mg2+; values of the developed force were normalized with respect to those in normal Krebs solution. Thus, B1 hypovitaminosis results in a decrease in the efficacy of neuromuscular synaptic transmission. Some neurological symptoms typical of a deficiency of vitamin B1 in the organism can be related to this effect.

Effects of Pyridoxal 5′-Phosphate on Synaptic Transmission in Smooth Muscle

We studied the influence of the vitamin B6 form most extensively distributed in the organism, pyridoxal 5′-phosphate (PyrP), on neuromuscular transmission in the smooth muscle of the circular layer of the guinea pig distal colon and of the ileum and an initial segment of the jejunum of humans. Application of 10-10 to 10-3 M PyrP reversibly and in a dose-dependent manner decreased the amplitude of non-cholinergic non-adrenergic inhibitory synaptic potentials (ISP) and increased their duration. Under the influence of 10-8 to 10-4 M PyrP, both the amplitude and duration of ATP- and noradrenaline-induced hyperpolarizations increased. Application of 10-4 M PyrP completely suppressed the sensitivity of smooth muscle cells to noradrenaline, but a hyperpolarizing effect of exogenous ATP was preserved. The PyrP-induced amplitude decrease and prolongation of ISP were preserved in the presence of 10-4 M hexonium (a ganglioblocker), 5 · 10-7 M apamin (a blocker of Ca2+-dependent K+ channels of small conductance), 10-5 M verapamil (a blocker of L-type Ca2+ channels), and 10-4 M Nω-nitro-L-arginine (a blocker of NO-synthase). It seems probable that a decrease in the ISP amplitude is related to a presynaptic PyrP effect. Under conditions of PyrP-induced suppression of non-cholinergic non-adrenergic inhibition, non-cholinergic short-latency excitatory synaptic potentials could be recorded in smooth muscle. Thus, PyrP is an effective modulator of synaptic transmission in smooth muscle of the gastrointestinal tract of mammals.

Effects of haloperidol, clotrimazole, and pyridoxal-5′-phosphate on synaptic transmission in smooth muscles of the human colon

In strips of smooth muscles of the human colon, haloperidol (Hal) and clotrimazole (Clo), in contrast to pyridoxal-5′-phosphate (PP), suppressed spontaneous electrical and contractile activities of these strips and also post-inhibitory excitation developing after inhibitory synaptic potentials (ISPs). Haloperidol, Clo, PP, and PP applied against the background of the action of Nω-nitro-L-arginine noticeably changed the parameters of ISPs. The pattern of effect of Hal on synaptic inhibition in smooth muscles was preserved against the background of the action of PP, and that of PP was preserved against the background of the action of Hal.

Effects of haloperidol and clotrimazole on synaptic transmission in and contractile activity of smooth muscles of the guinea-pig intestine

In muscle strips of the guinea-pig large intestine, haloperidol and clotrimazole increased spontaneous electrical and contractile activities and decreased ATP-evoked hyperpolarization of smooth-muscle cells and the amplitude of inhibitory synaptic potentials. The pattern of effects of haloperidol on hyperpolarization induced by intramural stimulation of muscle strips was preserved under conditions of pre-incubation of the preparations in Krebs solutions containing pyridoxal-5′-phosphate, Nω-nitro-L-arginine, or apamin, as well as both apamin and tetraethylammonium.

Effects of Pyridoxal-5′-Phosphate and Haloperidol on Synaptic Transmission in Human Colon Smooth Muscle

1 Bogomolets National Medical University, Kyiv, Ukraine. Correspondence should be addressed to M. M. Grusha (e-mail: mishagru@stenos.kiev.ua). Vitamin B 6 (pyridoxal), pyridoxal-5′-phosphate (PyrP), and haloperidol are drugs that can significantly influence the gastrointestinal motility in humans. A modified sucrose-gap technique was used in our experiments conducted on atropinized muscle strips isolated from the circular muscle layer of visually intact regions of the human ascendens, transversum, descendens, or sigmoideum colonic tissue removed in the course of surgical interventions caused by cecum, sigmoid, or rectum cancer. Spontaneous electrical activity was recorded in 85% of the cases. Inhibitory synaptic potentials (ISP) consisted of a single “fast” component and two-component ISP (including “fast” and “slow” components) were observed in 51 and 49% of the cases, respectively. Post-ISP depolarization waves with action potentials on their crests were found in 38% on the examined muscle strips, and depolarization at the boundary between the components of two-component ISP was observed in 32% of the cases. In experiments with drug application on muscle strips, control values of the analyzed parameters were taken as 100%. After 1to 5-min-long application of PyrP (1 · 10 M), the amplitude of ISP decreased to 86 ± 4, in 6-10 min to 73 ± 6% (n = 8), in 11-15 min to 68 ± 6% (n = 7), in 16-20 min to 57 ± 5, and in 21-25 min to 46 ± 7% (n = 4). After 6to 10-min-long application of PyrP, the latency of ISP increased to 128 ± 9% (n = 7), in 11-15 min to 135 ± 2% (n = 5), and in 16-20 min to 144 ± 8% (n = 4). Simultaneously, PyrP significantly increased the ISP duration (n = 8) and suppressed post-ISP depolarization waves with action potentials on their crests and depolarizations at the boundary between two components of complex ISP. Pyridoxal (1 · 10 M) less effectively than PyrP decreased the ISP amplitude. After 11to 15-min-long application of haloperidol (1 · 10 M), the amplitude of ISP decreased to 67 ± 8, in 16-20 min to 50 ± 7% (n = 7), in 21-25 min to 34 ± 7, in 26-30 min to 25 ± 7% (n = 6), in 36-40 min to 3 ± 2% (n = 5), and after 46to 50-min-long applications the amplitude dropped to zero (n = 5). After 16to 20-min-long application of haloperidol, the time of half-decay of ISP decreased to 74 ± 3 % (n = 6), spontaneous electrical activity and post-ISP depolarization waves with action potentials disappeared (n = 7), as well as depolarizations interposed between the components of two-component ISP did. The latency of ISP increased to 129 ± 2% (n = 5) in 26-30 min. The tested drugs can be considered effective modulators of synaptic transmission in the colonic smooth muscles.