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

Abstract

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 М) 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.

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

“…To record the electrical activity from MSs and also ISPs induced by intramural stimulation of MSs by rectangular current pulses of supramaximum intensity (duration 0.5 to 1.0 msec), we used a sucrose-gap technique. Absolute values of the recorded ISP parameters were similar to those in MSs obtained from the human large intestine and coincided with those described in our earlier study [2]. The contractile activity of MSs was recorded using a mechanotronic sensor.…”

“…Experiments were carried out on muscle strips (MSs) isolated from the circular layer of visually normal fragments of the human large intestine obtained in the course of abdominal surgery related to different diseases of the intestine [2]. Samples were taken from 28 patients (19 to 81 years old) at distances of several tens of centimeters from a damaged zone in the digestive tract.…”

“…A blocker of the latter receptors, MRS 2179, and a blocker of calcium-dependent potassium channels of small conductivity, apamin, decrease significantly the fast components of ISPs and also ATP-mediated hyperpolarization of smoothmuscle cells of the human intestine [1]. In SMs of the human large and small intestines, synaptic inhibition is also suppressed by an endogenous derivative of vitamin В 6 , pyridoxal-5′-phosphate (PP), considered to be a blocker of Р 2 purinoreceptors [2,3]. This effect of PP is weakened by an antagonist of vitamin В 6 , isoniazid (an anti-TBC preparation) [4].…”

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

“…10 -6 M atropine [1]. We used a single sucrose-gap technique to record electrical phenomena from MSs, in particular ISPs evoked by intramural stimulation of these strips.…”

“…The above receptors are sensitive to pyridoxal-5´-phosphate (PP) [1], and the mentioned channels can be blocked by apamin [2]. The second, slow, apamin-insensitive component is mediated by the action of such neurotransmitter as nitric oxide (NO) and develops due to activation of calciumdependent big-conductance potassium channels blocked by tetraethylammonium (TEA) [2].…”