Evidence for the role of phosphatidylcholine-specific phospholipase C in sustained hypoxic pulmonary vasoconstriction.

The aim of the study was to investigate the role of phosphatidylcholine-specific phospholipase C (PC-PLC) in hypoxic pulmonary vasoconstriction (HPV) and elucidate its possible interactions within HPV mechanism. Inhibition of PC-PLC with D609 (30µM) resulted in partial reduction of the transient phase and almost complete abolition of the sustained phase of HPV in isolated rat intrapulmonary arteries (IPAs). Intravenous injection of D609 (5mg/kg) 30min before the onset of hypoxia prevented the development of acute hypoxic pulmonary hypertension (AHPH) in rats. D609 also inhibited pulmonary vasoconstriction induced with a generator of superoxide anions LY83583, but not the one induced with hydrogen peroxide. Protein kinase C (PKC) inhibition with Ro-31-8220 partially diminished the transient phase of hypoxic contraction in IPA while the sustained phase remained unchanged. Phosphocholine, known to be released due to phosphatidylcholine breakdown by PC-PLC, induced sustained contraction in isolated IPA and also transient pulmonary and systemic hypertension if administered intravenously (70mg/kg). We conclude that PC-PLC plays an important role in sustained HPV possibly through the activation of PKC-independent mechanism, which may be coupled with phosphocholine release.

Smooth muscle of telokin-deficient mice exhibits increased sensitivity to Ca2+ and decreased cGMP-induced relaxation.

Cyclic nucleotides can relax smooth muscle without a change in [Ca2+]i, a phenomenon termed Ca2+ desensitization, contributing to vasodilation, gastrointestinal motility, and airway resistance. The physiological importance of telokin, a 17-kDa smooth muscle-specific protein and target for cyclic nucleotide-induced Ca2+ desensitization, was determined in telokin null mice bred to a congenic background. Telokin null ileal smooth muscle homogenates compared to wild type exhibited an approximately 30% decrease in myosin light-chain phosphatase (MLCP) activity, which was reflected in a significant leftward shift (up to 2-fold at pCa 6.3) of the Ca2+ force relationship accompanied by an increase in myosin light-chain phosphorylation. No difference in the Ca2+ force relationship occurred in telokin WT and knockout (KO) aortas, presumably reflecting the normally approximately 5-fold lower telokin content in aorta vs. ileum smooth muscle. Ca2+ desensitization of contractile force by 8-Br-cGMP was attenuated by 50% in telokin KO intestinal smooth muscle. The rate of force relaxation reflecting MLCP activity, in the presence of 50 microM 8-Br-cGMP, was also significantly slowed in telokin KO vs. WT ileum and was rescued by recombinant telokin. Normal thick filaments in telokin KO smooth muscles indicate that telokin is not required for filament formation or stability. Results indicate that a primary role of telokin is to modulate force through increasing MLCP activity and that this effect is further potentiated through phosphorylation by cGMP in telokin-rich smooth tissues.

[Effect of nitroglycerin on vasodilation at high altitude]. / Usilenie vazodilatatsii na nitroglitserin v usloviiakh vysokogor'ia.

After more than centenary successful use of nitroglycerin in clinical practice, scientists revealed that its medicinal effect is based on release of potent vasodilator nitric oxide (NO). Moreover, the experiments showed that NO plays an important role in hypoxia vasodilator mechanisms. Since nitroglycerin is an exogenous NO donor and moderate hypoxia facilitates release of endogenous NO, we suggested that nitroglycerin effects are changed in high altitude. To examine this suggestion, we have carried out a standard nitroglycerin test for healthy volunteers living in high and low altitude areas. Comparison of obtained results showed that the use of oral nitroglycerin in high altitude areas is accompanied with significant prolonged decrease in blood pressure and total vascular resistance. So, we first found that high altitude hypoxia strengthens and extends nitroglycerin-induced peripheral vasodilation in healthy subjects. This effect might be caused by additive vasodilator effect of nitroglycerin and moderate hypoxia. This data should be taken into account when prescribing exogenous and endogenous NO donors to treat patients in high altitude areas.

Saline containing phosphatidylcholine liposomes possess the ability to restore endothelial function damaged resulting from gamma-irradiation.

The protective action of passive saline filled ("empty") phosphatidylcholine liposomes (PCL) on endothelial function was examined in thoracic aortas obtained from gamma irradiated (6 Gy) Chinchilla rabbits, and then verified in experiments on non-anesthetized and anesthetized rats. Acetylcholine (ACh)-induced vascular relaxant responses in isolated vascular tissues rats were used as the test of endothelial integrity and its functional ability. It was shown that when added to the bath solution (100 microg/ml), PCL effectively restored endothelium-dependent ACh relaxations of isolated vascular rings damaged resulting from gamma-irradiation but had no effect on endothelium-independent vascular responses to therapeutic nitric oxide (NO) donors. The liposomes were also without protective effect when injected to the rabbits intraperitoneally (30 mg/kg) 1 hour before irradiation. In contrast, PCL, being injected at the same dose 1 hour after radiation impact, promote normalization of both endothelium-dependent vascular responses to ACh and nitric oxide (NO) donors. PCL restored also the sensitivity of vascular tissues to authentic NO (aqueous NO solution) that was surprisingly increased after irradiation, and normalized relationship between ACh-stimulated NO release and relaxant response amplitudes in irradiated aortas. Experiments on non-anesthetized and anesthetized rats demonstrated that irradiation led to significant elevation in the level of arterial blood pressure without any changes in cardiac contractility. PCL administration (25 mg/kg, i.v.) effectively normalized an increased arterial blood pressure in irradiated animals. In conclusion, it appears that PCL due to its ability to normalize NO-dependent vascular tone control mechanisms might be worthwhile therapeutic approach in case of ionizing irradiation accident. These result support the concept that the depression of endothelium-dependent vascular responses after irradiation may be result of decreased NO bioavailability due to its conversion to less potent vasodilators during irradiation-induced oxidative attack.

Photolytic release of MgADP reduces rigor force in smooth muscle.

Photolytic release of MgADP (25-300 microM) from caged ADP in permeabilized tonic (rabbit femoral artery-Rfa) and phasic (rabbit bladder-Rbl) smooth muscle in high-tension rigor state, in the absence of Ca(2+), caused an exponential decline (approximately 1.5% in Rfa and approximately 6% in Rbl) of rigor force, with the rate proportional to the liberated [MgADP]. The apparent second-order rate constant of MgADP binding was estimated as approximately 1.0 x 10(6) M(-1) s(-1) for both smooth muscles. In control experiments, designed to test the specificity of MgADP, photolysis of caged ADP in the absence of Mg(2+) did not decrease rigor force in either smooth muscle, but rigor force decreased after photolytic release of Mg(2+) in the presence of ADP. The effects of photolysis of caged ADP were similar in smooth muscles containing thiophosphorylated or non-phosphorylated regulatory myosin light chains. Stretching or releasing (within range of 0.1-1.2% of initial Ca(2+)-activated force) did not affect the rate or relative amplitude of the force decrease. The effect of additions of MgADP to rigor cross-bridges could result from rotation of the lever arm of smooth muscle myosin, but this need not imply that ADP-release is a significant force-producing step of the physiological cross-bridge cycle.

Contractile properties and proteins of smooth muscles of a calponin knockout mouse.

The role of h1-calponin in regulating the contractile properties of smooth muscle was investigated in bladder and vas deferens of mice carrying a targeted mutation in both alleles designed to inactivate the basic calponin gene. These calponin knockout (KO) mice displayed no detectable h1-calponin in their smooth muscles. The amplitudes of Ca2+ sensitization, force and Ca2+ sensitivity were not significantly different in permeabilized smooth muscle of KO compared with wild-type (WT) mice, nor were the delays in onset and half-times of Ca2+ sensitization, initiated by flash photolysis of caged GTPgammaS, different. The unloaded shortening velocity (Vus) of thiophosphorylated fibres was significantly (P<0.05) faster in the smooth muscle of KO than WT animals, but could be slowed by exogenous calponin to approximate WT levels; the concentration dependence of exogenous calponin slowing of Vus was proportional to its actomyosin binding in situ. Actin expression was reduced by 25-50%, relative to that of myosin heavy chain, in smooth muscle of KO mice, without any change in the relative distribution of the actin isoforms. We conclude that the faster Vus of smooth muscle of the KO mouse is consistent with, but does not prove without further study, physiological regulation of the crossbridge cycle by calponin. Our results show no detectable role of calponin in the signal transduction of the Ca2+-sensitization pathways in smooth muscle.

Myosin essential light chain isoforms modulate the velocity of shortening propelled by nonphosphorylated cross-bridges.

The differential effects of essential light chain isoforms (LC17a and LC17b) on the mechanical properties of smooth muscle were determined by exchanging recombinant for endogenous LC17 in permeabilized smooth muscle treated with trifluoperazine (TFP). Co-precipitation with endogenous myosin heavy chain verified that 40-60% of endogenous LC17a could be exchanged for recombinant LC17a or LC17b. Upon addition of MgATP in Ca2+-free solution, recombinant LC17 exchange induced slow contractions unaccompanied by regulatory light chain (RLC) phosphorylation only in TFP-treated, but not in untreated, permeabilized smooth muscle; the shortening velocity and rate of force development were approximately 1.5 and 2 times faster, respectively, in response to LC17a than LC17b. Additional incubation with recombinant, thiophosphorylated RLC increased the shortening velocity, independent of the LC17 isoform exchanged. The LC17-induced contractions of TFP-treated muscles were abolished by prior addition of nonphosphorylated RLC. We suggest that LC17 stiffens the lever arm of myosin and, in the absence of regulation by RLC, permits cross-bridge cycling without requiring RLC phosphorylation. Our results are compatible with nonphosphorylated RLC acting as a repressor and with LC17 isoforms modulating the MgADP affinity and, consequently, rate of cooperative cycling of nonphosphorylated cross-bridges.

Thiophosphorylation of myosin light chain increases rigor stiffness of rabbit smooth muscle.

1. The effect of thiophosphorylation of the regulatory myosin light chain (MLC20) on rigor stiffness was determined in permeabilized rabbit bladder smooth muscle. 2. Rigor stiffness of alpha-toxin-permeabilized smooth muscle was significantly increased by thiophosphorylation of MLC20. This increase may have been due to partial shortening (melting) in the proximal rod region and/or stiffening of the regulatory domain of the myosin head. 3. We suggest that phosphorylation of MLC20, by increasing the stiffness of the S1 lever arm and/or S2 hinge regions of the myosin molecule, favours separation of the two phosphorylated heads and consequent deinhibition of motor domain activity.

Regulation of the cross-bridge cycle: the effects of MgADP, LC17 isoforms and telokin.

This review summarizes the role of MgADP in force maintenance by dephosphorylated cross-bridges in smooth muscle and a potential physiological role for telokin. In tonic, compared with phasic, smooth muscles the affinity of cross-bridges in approximately 5 times higher for MgADP and the apparent second-order rate constant for MgATP is approximately 3 times lower. This gives rise to a large population of dephosphorylated cross-bridges in tonic smooth muscle. Such cross-bridges are thought to be major determinants of the different relaxation kinetics of the two types of smooth muscle and contribute to force maintenance at low levels of MLC20 phosphorylation, termed 'catch-like state' (Somlyo & Somlyo 1967) or 'latch' (Dillon et al. 1981). The molecular basis of the different affinities for MgADP and MgATP between tonic and phasic smooth muscle myosin was explored by exchange of essential myosin light chain (LC17) isoforms. In phasic bladder smooth muscle the exchange of LC17b for LC17a caused a significant decrease in the unloaded shortening velocity of non-phosphorylated, slowly cycling cross-bridges, suggesting that the LC17 isoforms contribute to the nucleotide affinity of latch bridges. The role of telokin in Ca(2+)-desensitization in phasic smooth muscle is reviewed. Telokin, the independently expressed C-terminus of myosin light chain kinase, is extensively phosphorylated during forskolin- and 8-br-cGMP-induced relaxation in situ. Telokin accelerated dephosphorylation of the regulatory myosin light chain and relaxed rabbit ileum smooth muscle. The results suggest that telokin contributes to cAMP and/or cGMP kinase-mediated Ca(2+)-desensitization of phasic smooth muscles.

Nucleotide binding by actomyosin as a determinant of relaxation kinetics of rabbit phasic and tonic smooth muscle.

1. The apparent second-order rate constants (k+T) of ATP-induced cross-bridge detachment from rigor in the absence of Ca2+ were determined with laser flash photolysis of caged ATP (cATP) in alpha-toxin-permeabilized tonic, rabbit femoral artery and phasic, rabbit bladder smooth muscles. The potential effect of cATP binding to actomyosin (AM) on cross-bridge kinetics was examined by varying the initial concentration of cATP 2-fold. For a given [ATP] released from either 10 or 5 mM cATP, the kinetics of relaxation were not significantly different; the estimated dissociation constant for cATP binding to smooth muscle AM was 1-3 mM. 2. k+T was significantly higher ((9.5 +/- 1.3) x 10(4) M-1 s-1) in the phasic than in the tonic ((3.0 +/- 1.0) x 10(4) M-1 s-1) smooth muscle. 3. We conclude that the combination of the significantly lower (approximately 3 times) apparent second-order rate constant of MgATP association with the approximately 5 times higher affinity of cross-bridges for MgADP in tonic, than in phasic, smooth muscle is a major determinant of the slower kinetics of relaxation and, probably, shortening velocity of tonic smooth muscle.

[The current malariological situation in the countries of western Africa. 1. The Republic of Guinea]. / Sovremennaia maliariologicheskaia situatsiia v stranakh Zapadnoi Afriki. Soobshchenie 1. Gvineiskaia Respublika.

Favorable climatic conditions in the Republic of Guinea are conducive to a high prevalence of infectious and parasitic diseases, responsible for 70% of primary consultations of the population, malaria being diagnosed in 40% of cases. Five landscape malariologic zones were singled out in the country, that are characterized by a certain level of malariogenicity. In the lowland/river and mountain/river zones the parasite index of children aged 2 to 9 varied from 16.4 to 45%, and in some foci it reached 63.1%. Foci in the Guinea-Sudan type wet savanna zone are also referred to meso- and hyperendemic ones. The mountain/forest zones are mainly mesoendemic. Malaria foci in the forest/savanna zone in southern Guinea and in the Sierra Leone northern provinces are hyper- and holoendemic, with the parasite index of children aged 2 to 9 being 76.3-92%.

[Prevention of postischemic lesions of the myocardium using liposomes]. / Preduprezhdenie postishemicheskikh povrezhdenii miokarda s pomoshch'iu liposom.

The experiments on dogs showed that 60-min blood flow restriction in the left coronary artery branch resulted in pumping and contractile heart dysfunctions. The removal of the blood flow barrier caused reinforcement of the above dysfunctions. The administration of 50 mg/kg liposome prior to reperfusion improved pumping and contractile heart functions and allowed maintenance of stable hemodynamics during the reperfusion.

[Various mechanisms of circulatory failure in septic shock]. / Nekotorye mekhanizmy nedostatochnosti krovoobrashcheniia pri septicheskom shoke.

The main parameters of hemodynamic and myocardial contractile activity, transcapillary fluid and proteins exchange have been studied in healthy and infected anaesthetized dogs with source of purulent infection during septic shock development. Besides, blood gas tension, pH and toxicity of blood and lymph are determined as well. It is shown that damage of microcirculation promoting tissue hypoxia and endogenous intoxication, is responsible for the initiation of decompensating disturbance of circulation at pus process generalization.

The influence of the rate of rigor state development on its tension in single muscle fibre.

The rigor tension and stiffness of glycerinated fibres from rabbit psoas muscle were found to vary markedly in dependence on the rate of substitution of the solutions in the experimental chamber. The maximum value of rigor tension, which is close to that activated by Ca2+ with pCa4, was obtained at the slow development of rigor in the absence of Ca2+ ions. The observed dependence is assumed to be due to the different degrees of removal of the 'slack' in fibres, which may be contributed by compliant ends of the preparation. A new method allowing to obtain rather reproducible values of rigor tension is proposed.

[Shifts in the parameters of cardio- and hemodynamics and their correction using liposomes in the process of the development of septic shock]. / Sdvigi parametrov kardio- i gemodinamiki i ikh korrektsiia s pomoshch'iu liposom v protsesse razvitiia septicheskogo shoka.

The interdependence between changes in central cardiac hemodynamics and regional blood flow has been studied in dogs with experimental septic shock. Possible correction of the above damages by direct delivery of liposomes to tissues of the septic focus has been investigated. It has been found that vascular insufficiency is primary in the genesis of decompensated circulatory disturbances, with its progress leading to the inhibition of pump and contractility cardiac functions. Regional subcutaneous administration of liposomes in developing septic shock prevents the onset of cardiovascular disturbances.

[Maximum rigor tension developed in a single rabbit glycerinated skeletal muscle fiber]. / Maksimal'naia velichina rigornogo napriazheniia, razvivaemogo odinochnym demembranizirovannym voloknom skeletnoi myshtsy krolika.

Rigor tension was found to vary significantly with the replacement rate of the relaxing with the rigor solutions. The maximum value of rigor tension (Prig = 130 kN/m2) was obtained under slow (5 microL/sec) replacement of the solutions. The difference in the tensions may reflect variations in the amount of "compliance" taken out from the fibre.

["Freezing" of the conformation of thin filaments in a single skinned fiber of the rabbit muscle by glutaraldehyde]. / "Zamorazhivanie" konformatsii tonkikh nitei v odinochnykh demembranirovannykh voloknankh myshtsy krolika gliutarovym al'degidom.

It is shown that short treatment of a single skinned rigor fibre from rabbit m X psoas with 0.05% glutaraldehyde in the absence of Ca ions leads to a modified state of the contractile apparatus. After the addition of 5 mM MgATP in the absence of Ca ions to the fibre a sharp rise and subsequent slow decay of tension were observed in contrast to the tension drop in case of the control (unmodified) specimen. The tension transients following quick stretch (L 0.5%) were similar to those for Ca-activated tension. In case of the modified relaxed fibre such a phenomenon was not observed. These results can be explained by "freezing" with glutaraldehyde the thin filament structure either in the "on" or "off" states. The relation of these results to the cooperativity in the regulation mechanism of contraction is discussed.