TTX-sensitive Na(+) and nifedipine-sensitive Ca(2+) channels in rat vas deferens smooth muscle cells.

The inward currents in single smooth muscle cells (SMC) isolated from epididymal part of rat vas deferens have been studied using whole-cell patch-clamp method. Depolarising steps from holding potential -90 mV evoked inward current with fast and slow components. The component with slow activation possessed voltage-dependent and pharmacological properties characteristic for Ca(2+) current carried through L-type calcium channels (I(Ca)). The fast component of inward current was activated at around -40 mV, reached its peak at 0 mV, and disappeared upon removal of Na ions from bath solution. This current was blocked in dose-dependent manner by tetrodotoxin (TTX) with an apparent dissociation constant of 6.7 nM. On the basis of voltage-dependent characteristics, TTX sensitivity of fast component of inward current and its disappearance in Na-free solution it is suggested that this current is TTX-sensitive depolarisation activated sodium current (I(Na)). Cell dialysis with a pipette solution containing no macroergic compounds resulted in significant inhibition of I(Ca) (depression of peak I(Ca) by about 81% was observed by 13 min of dialysis), while I(Na) remained unaffected during 50 min of dialysis. These data draw first evidence for the existence of TTX-sensitive Na(+) current in single SMC isolated from rat vas deferens. These Na(+) channels do not appear to be regulated by a phosphorylation process under resting conditions.

[The generation of nonadrenergic inhibiting synaptic potentials in the smooth muscles of the gastrointestinal tract by substituting cesium ions for potassium ions]. / Generatsiia neadrenergicheskikh tormoziashchikh sinapticheskikh potentsialov v gladkikh myshtsakh zheludochno-kishechnogo trakta pri zamene ionov kaliia ionami tseziia.

Nonadrenergic inhibitory junction potentials (IJPs) evoked by intramural stimulation were investigated in smooth muscle of guinea pig stomach, caecum and colon by means of sucrose-gap method. IJPs disappeared in the smooth muscle preexposed to K-free Krebs solution for 4-9 h and restored by addition 6mM Cs+. The amplitude of IJPs was half as much as one in normal conditions but the latency and duration were significantly prolonged. In most cases apamin blocks IJPs in these muscles. The results presented suggest that IJPs generation is due to Cs+ ions permeated through Ca(2+)-activated apamin-sensitive potassium channels of small conductance in these conditions. As the responses to ATP were affected in parallel with IJPs, these results are consistent with the purinergic hypothesis.

Studies of the inhibitory non-adrenergic neuromuscular transmission in the smooth muscle of the normal human intestine and from a case of Hirschsprung's disease.

A modified sucrose-gap method was used to study both non-adrenergic inhibitory neuromuscular transmission and effects of adenosine 5'-triphosphate (ATP) on isolated smooth muscle preparations from the human intestine. It was found that non-adrenergic inhibition in the circular smooth muscle layer was of larger amplitude than in the longitudinal layer. Study of the ionic mechanisms underlying non-adrenergic inhibition indicated that an increase in K+ conductance was responsible for the generation of non-adrenergic inhibitory junction potentials (IJPs). The results suggest that the inhibitory actions of the endogenous neurotransmitter and exogenous ATP are due to increases in Ca2+-dependent K+ conductance. The K+-channel blockers tetraethylammonium and 4-aminopyridine had no effect on IJPs or ATP, while apamin slightly decreased both the amplitude of the IJP and the hyperpolarization of the circular smooth muscle caused by ATP. These results are consistent with the purinergic hypothesis of non-adrenergic inhibition. In addition to inhibitory purinoceptors, the existence of excitatory purinoceptors was identified in the longitudinal muscle, activation of which probably caused an increase in Na+-conductance. The excitatory purinoceptor-mediated contraction in the longitudinal muscle from the constricted region of large intestine from patients with Hirschsprung's disease was greater than that found in control specimens. It is possible that excitatory purinoceptors play a role in the pathophysiology of Hirschsprung's disease.

[Adrenergic regulation of contractile activity of smooth muscles in umbilical vessels]. / Adrenergicheskaia reguliatsiia sokratitel'noi aktivnosti gladkikh myshts sosudov pupoviny.

The effect of agonists and antagonists of alpha- and beta-adrenoreceptors on mechanical properties of the smooth muscle was studied in the isolated muscle strips of the human umbilical artery and vein. Noradrenaline was shown to cause the contraction of smooth muscles of the umbilical vein. Tonic and phase components in the contraction process were observed. Isoprenaline caused tonic contraction of the muscle strip. Phentolamine, and alpha-adrenoblocker did not inhibit the stimulating activity of noradrenaline. In presence of obsidane (beta-adrenoblocker) noradrenaline triggered the contraction with lesser tonic component as compared to the initial one. So the selective stimulation of beta-adrenoreceptors of smooth muscles of the umbilical vein by isoprenaline and blocking of the same receptors by obsidane have proved that activation of alpha-adrenoreceptors is responsible for the phasic component of contraction, while that of beta-adrenoreceptors--for the tonic component of contraction. As both alpha- and beta-adrenoblockers in smooth muscles of the umbilical artery inhibit the noradrenaline-induced contraction, it was concluded that the differentiation of adrenoreceptors of the vessel is rather low.

Pre- and postjunctional actions of purine and xanthine compounds in the guinea-pig caecum circular muscle.

1. The sucrose-gap technique was used to study pre- and postjunctional actions of P1-purinoceptor and P2-purinoceptor agonists and a range of xanthine derivatives in the guinea-pig caecum circular muscle. 2. Adenosine, 2-chloroadenosine (2-ClAd), ATP and alpha,beta-methylene ATP all caused concentration-dependent hyperpolarization of the smooth muscle membrane with a rank order of potency of 2-ClAd greater than alpha,beta-methylene ATP greater than adenosine. 3. The xanthine derivatives caffeine, theophylline, 8-phenyltheophylline and 1,3-dipropyl-8-(2-amino-4-chlorophenyl) xanthine (PACPX) at submicromolar concentrations evoked depolarization of the smooth muscle membrane. At higher concentrations, all these compounds and enprofylline caused concentration-dependent hyperpolarization. 4. All the purine compounds tested caused a reduction in the amplitude of the non-adrenergic, non-cholinergic inhibitory junction potential (i.j.p.). For the P1-purinoceptor agonists adenosine and 2-ClAd this was almost entirely a prejunctional effect. For the P2-purinoceptor agonists this was mostly a postjunctional effect because both ATP and alpha,beta-methylene ATP caused significantly greater increases in the conductance of the smooth muscle membrane than did adenosine or 2-ClAd. 5. All the xanthine compounds tested (up to 100 microM), except enprofylline, were capable of increasing the amplitude of the i.j.p. At millimolar concentrations both caffeine and theophylline could reduce the i.j.p. amplitude. 6. It is concluded that there are inhibitory prejunctional P1-purinoceptors on the i.j.p.-producing neurones in the guinea-pig caecum circular muscle and that, of the xanthine derivatives tested, none of them would be suitable to use as a P1-purinoceptor antagonist in this preparation because of their own direct effects.

[Synaptic processes in smooth muscles]. / Sinapticheskie protsessy v gladkikh myshtsakh.

Junction potentials evoked by intramural stimulation were investigated in smooth muscles of guinea-pig gastrointestinal tract by means of intracellular recording and sucrose-gap methods. It was shown that cholinergic nerve-muscle transmission is only excitatory and more effective in fundic smooth muscles as compared with other part of the gut. Adrenergic nerve control of gastrointestinal motility is carried out both by excitation and inhibition of the smooth muscles. Nonadrenergic inhibition was observed in circular muscle layer of all parts of the gut and was more effective in distal colon. Noncholinergic, nonadrenergic excitation in caecum smooth muscles is shown to be of complex nature. It consists of an initial excitatory junction potential followed by a slow late wave of depolarization. In other parts of the gastrointestinal tract such an excitation is manifested only by a slow late wave of depolarization.

[Effect of strychnine, hydrastine and apamin on synaptic transmission in smooth muscle cells]. / Vliianie strikhnina, gidrastina i apamina na sinapticheskuiu peredachu v gladkomyshechnykh kletkakh.

The effects of strychnine, hydrastine and apamine on nervemuscle transmission in guinea pig stomach and taenia coli were studied. Hydrastine and strychnine produced an increase in non-adrenergic IPSPs of smooth muscle cells. Under apamine action IPSPs and hyperpolarization caused by exogenous ATP were reversibly blocked and non-cholinergic EPSPs appeared. ATP caused depolarization of the cell membrane in this condition. Consequently, apamine is a specific (postsynaptic) blocking agent of non-adrenergic inhibition and ATP obviously mediates both non-adrenergic inhibition and non-cholinergic synaptic excitation of smooth muscle cells observed in our experiments.