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.

Rho kinase and protein kinase C involvement in vascular smooth muscle myofilament calcium sensitization in arteries from diabetic rats.

BACKGROUND AND PURPOSE: Diabetes mellitus (DM) causes multiple dysfunctions including circulatory disorders such as cardiomyopathy, angiopathy, atherosclerosis and arterial hypertension. Rho kinase (ROCK) and protein kinase C (PKC) regulate vascular smooth muscle (VSM) Ca(2+) sensitivity, thus enhancing VSM contraction, and up-regulation of both enzymes in DM is well known. We postulated that in DM, Ca(2+) sensitization occurs in diabetic arteries due to increased ROCK and/or PKC activity. EXPERIMENTAL APPROACH: Rats were rendered hyperglycaemic by i.p. injection of streptozotocin. Age-matched control tissues were used for comparison. Contractile responses to phenylephrine (Phe) and different Ca(2+) concentrations were recorded, respectively, from intact and chemically permeabilized vascular rings from aorta, tail and mesenteric arteries. KEY RESULTS: Diabetic tail and mesenteric arteries demonstrated markedly enhanced sensitivity to Phe while these changes were not observed in aorta. The ROCK inhibitor HA1077, but not the PKC inhibitor chelerythrine, caused significant reduction in sensitivity to agonist in diabetic vessels. Similar changes were observed for myofilament Ca(2+) sensitivity, which was again enhanced in DM in tail and mesenteric arteries, but not in aorta, and could be reduced by both the ROCK and PKC blockers. CONCLUSIONS AND IMPLICATIONS: We conclude that in DM enhanced myofilament Ca(2+) sensitivity is mainly manifested in muscular-type blood vessels and thus likely to contribute to the development of hypertension. Both PKC and, in particular, ROCK are involved in this phenomenon. This highlights their potential usefulness as drug targets in the pharmacological management of DM-associated vascular dysfunction.

[Effect of ionising irradiation on outward potassium current in the aorta smooth muscle cells in rats: the role of protein kinase C].

It is known that gamma-irradiation leads to vascular hyperfunction and hypertension development. In this study we tested the hypothesis that ionizing irradiation directly affects vascular smooth muscle cells due to damage in outward K+ channel function. The goal of this study was to evaluate the influence of whole-body ionizing irradiation (6 Gy dose) on Ca(2+) dependent K+ channels and to clarify a possible involvement of protein kinase C in this process. Experiments were conducted on isolated rat aorta smooth muscle cells using whole-cell patch clamp technique. It has been shown that the basic component of outward K+ current in rat aortic smooth muscle cells is a large conductance Ca(2+)-activated K+ current (BK(Ca)). BK(Ca) currents in smooth muscle cells obtained from irradiated animals on the 9th and 30th days post-irradiation demonstrated a significant decrease of K(+)-current density amplitudes. Protein kinase C inhibitor, chelerythrine, effectively restored BK(Ca) current reduced by ionizing irradiation. In conclusion, the results suggest that gamma-irradiation suppressed BK(Ca) current in vascular smooth muscle cells, and this effect is mainly due to activation of protein kinase C.

[Modern conception of protein kinase C role in the vascular smooth muscles tone regulation].

Protein kinase C is an important regulatory enzyme that plays significant role in the vascular tone regulation. Protein kinase C is involved in the vascular smooth muscle cells (SMC) contractility at physiological conditions and its hyperreactivity at different types of pathology. Myogenic and endothelium-dependent pathways of protein kinase C-mediated vascular tone regulation include a variety of cellular mechanisms. The most important protein kinase C-mediated mechanisms in SMC are the increase of myophilament Ca2+-sensitivity; regulation of plasmolema ion permeability, and proliferative changes in SMC. Protein kinase C-related mechanisms in vascular endotheliocytes include regulation of formation and transduction of humoral and electrical signals to SMC that play an important role in the pathological vasospasm development.

[Effect of inhibition of glycolysis and myoendothelial electrical coupling on contractile responses of pulmonary artery and aorta during hypoxia in rats]. / Vplyv blokady hlikolizu ta mioendotelial'noho elektrychnoho zv'iazku na rozvytok skorotlyvykh reaktsii stinky lehenevykh arterii ta aorty shchuriv pid diieiu hipoksiï.

The effects of blockade of glycolysis on the contractile activity of isolated vascular rings of both the pulmonary artery and, the thoracic aorta were studied under hypoxia in intact, denuded vessels and those with blocked myoendothelial electrical coupling. The blockade of glycolysis led to a reversion of a hypoxic contraction in the pulmonary artery but had no effect on hypoxic dilatation of the aorta. Hypoxic constriction of the pulmonary artery was abolished after denudation and stayed unchanged at the following blockade of glycolysis. Moreover, blockade of glycolysis had no effect on the hypoxic responses of the pulmonary artery after blockade of the myoendothelial gap junctions. The data suggest that hypoxic contraction of the pulmonary artery is endothelium-dependent, in contrast to the hypoxic dilatation of the aorta. It is likely that glycolysis in endothelial cells and myoendothelial gap junctions contribute to hypoxic pulmonary vasoconstriction due to formation and conduction the depolarizing electrical signals from endothelial cells to smooth muscles causing their contraction under hypoxia.

[Current concepts on the mechanisms of hypoxic effects on vascular tonus]. / Suchasni uiavlennia pro mekhanizmy vplyvu hipoksiï na tonus krovonosnykh sudyn.

It is well known that hypoxia causes smooth muscle relaxation of the majority of mammalian systemic blood vessels, whereas smooth muscles in the pulmonary and large coronary arteries constrict under hypoxia. The review describes a modern concept of the mechanisms involved in the hypoxic vasoconstriction and vasodilatation. Cationic channels of a plasma membrane, the contractile apparatus, and mitochondria are the main oxygen sensors in the vascular smooth muscle cells. Hypoxic vasodilatation is mediated mainly by a decrease in the voltage-dependent Ca2+ entry, decrease in Ca2+ sensitivity of the contractile apparatus, and activation of ATP-dependent K+ channels. This process also involves endothelium derived nitric oxide. Hypoxic vasoconstriction mechanisms may be related to voltage-gating K+ channels inhibition, Ca2+ release from intracellular stores and inactivation of Ca2+ activated K+ channels each of them leads to increase in intracellular Ca2+ concentration. Platelet-activating factor, prostaglandins F2 alpha, E2, tromboxan B2, leucotriens C4 and D4 also contribute to hypoxic vasoconstriction. Glycolysis which intensity increases in hypoxia, and electron transport chain which generates the reactive oxygen species play the important role in the development of hypoxic pulmonary vasoconstriction. They possess the ability to change redox state in the cells and therefore to modulate the activity of the cationic channels. Hypoxia also leads to a proliferation of smooth muscles in the vascular wall. Better understanding of the underlying hypoxia-related mechanisms is vital for the explanation of enhanced blood flow under hypoxia, and is absolutely necessary for creating new effective antihypoxic drugs.