Effect of pH Change on Vascular Smooth Muscle Contractility in Rat Superior Mesenteric Artery and Its Branches / 대한흉부외과학회지

BACKGROUND: Extracellular and intracellular pH (pHo and pHi), which can be changed in various pathological conditions such as hypoxia, affects vascular contractility. To elucidate the mechanism to alter vascular contractility by pH, the effects of pH on reactivity to vasocontracting agents, intracellular Ca2+ influx, and Ca2+ sensitivity in vascular smooth muscle were examined. MATERIAL AND METHOD: Isometric contractions in rat superior mesenteric arteries (SMA) were observed. Intracellular Ca2+ concentration ([Ca2+]i) was recorded by microfluorometer using Fura-2/acetoxylmethyl ester in muscle cells. pHo was increased from 7.4 to 7.8 or decreased to 6.9 or 6.4. pHi was decreased by applying NH4+ or propionic acid or modulated by changing pHo after increasing membrane permeability using beta-escin. RESULT: Decreases in pHo from 7.4 to 6.9 or 6.4 shifted concentration-response curve by norepinephrine (NE) or serotonin (SE) to the right and significantly increased half maximal effective concentration (EC50) to NE or SE. Increase in pHo from 7.4 to 7.8 shifted concentration-response curve by norepinephrine (NE) or serotonin (SE) to the left and significantly reduced EC50 to NE or SE. NE increased [Ca2+]i in cultured smooth muscle cells from SMA and the increased [Ca2+]i was reduced by decreases in pHo. NE-induced contraction was inhibited by NH4+, whereas the resting tension was increased by NH4+ or propionic acid. When the cell membrane of SMA was permeabilized using beta-escin, SMA was contracted by increasing extracellular Ca2+ concentration from 0 to 10micrometer and the magnitude of contraction was decreased by a decrease in pHo and vice versa. CONCLUSION: From these results, it can be concluded that a decrease in pHo might inhibit vascular contraction by reducing the reactivity of vascular smooth muscle to vasoactive agents, Ca2+ influx and the sensitivity of vascular smooth muscle to Ca2+.

Relaxation Response of Rabbit Cavernous Smooth Muscle to Estrogen / 대한남성과학회지

PURPOSE: Estrogen relaxes vascular smooth muscle via genomic and non-genomic mechanisms. Most studies of the role of estrogen in the relaxation response have been conducted in females, and little information is available in males. This study investigated whether estrogen plays a role in relaxation of the rabbit cavernous smooth muscle. MATERIALS AND METHODS: Relaxation responses of rabbit cavernous smooth muscle to estrogen (30 nM, 300 nM, 3 micrometer, 30 micrometer) were observed in vitro. The responses of the muscle strips to estrogen after incubation with the transcription inhibitor dactinomycin (10 micrometer) or the nonspecific nitric oxide (NO) synthase inhibitor L-NAME (10 micrometer) also were evaluated. RESULTS: Estrogen caused dose-dependent relaxation of strips contracted by norepinephrine. The maximal response was seen about 10 minutes after treatment. Estrogen-induced relaxation was not prevented by dactinomycin or L-NAME, suggesting that the response was not mediated by gene transcription or NO. CONCLUSIONS: Estrogen may be involved in relaxation of rabbit cavernous smooth muscle via a non-genomic NO-independent mechanism.

The effect of carbon monoxide on contraction, cytosolic Ca2+ level and ionic currents in guinea pig ileal smooth muscle

The aim of this study was to clarify the mechanism of the inhibitory action of carbon monoxide (CO) on contraction, by measuring cytosolic Ca2+ level ((Ca2+)i) and ionic currents in guinea-pig ileum. CO (10%) inhibited 40 mM KCl-induced contraction and this effect was blocked by ODQ (1 micrometer), a soluble guanylyl cyclase (sGC) inhibitor. CO inhibited the 40 mM KCl-induced contraction without changing (Ca2+)i. Cumulative addition of KCl induced a graded increase in (Ca2+)i and muscle tension. In the presence of CO, cumulative addition of KCl induced smaller contraction than in the absence of CO. On the other hand, the increase in (Ca2+)i induced by cumulative addition of KCl was only slightly decreased in the presence of CO, and the (Ca2+)i-tension relationship shifted downwards. Using the patch clamp technique with a holding potential of -60 mV, we found that CO had little effect on the peak Ba currents (IBa) when voltage was stepped from -60 mV to 0 mV. In addition, CO showed no effect on the depolarization-activated outward K+ currents in the all potential ranges. We conclude that CO inhibits smooth muscle contraction mainly by decreasing the Ca2+ sensitivity of contractile elements via a cGMP-dependent pathway, not by involving L-type Ca2+ and outward-potassium currents in guinea-pig ileum.

Involvement of Spontaneously Formed Cyclic Nucleotides in Cat Gastric Muscle Relaxation

Muscle strips and muscle cells from cat stomach were used to investigate whether spontaneously formed cyclic nucleotides were involved in the inhibition of gastric smooth muscle contraction. A phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX), increased the levels of both cyclic GMP (cGMP) and cyclic AMP (cAMP) in resting state cells, while decreasing acetylcholine-induced muscle contraction. Under the influence of IBMX, SQ22536, an adenylyl cyclase inhibitor and methylene blue, a guanylyl cyclase inhibitor completely blocked increases in cAMP and cGMP respectively, without any effect on contraction. However, the combination of SQ22536 and methylene blue completely blocked increases in both cAMP and cGMP levels and stimulated contractions markedly even in the presence of IBMX. Muscle contraction inhibitors such as isoprenaline, vasoactive intestinal polypeptide and sodium nitroprusside also appeared to increase cyclic nucleotide levels which decreased contraction. Which nucleotide increased the most was dependent on the agonist used. Therefore, irrespective of the cyclic nucleotide class, the spontaneous formation of cyclic nucleotides should be considered in evaluating the mechanism of gastric smooth muscle relaxation.

The Effects of Glucose , Insulin and Angiotensin II on Plasminogen Activator Inhibitor-1 Expression and Growth of Aortic Vascular Smooth Muscle Cell in Rats / 대한흉부외과학회지

BACKGROUND: Plasminogen activator inhibitor-1(PAI-1) is known as the primary physiological inhibitor of tissue-type plasminogen activator(t-PA) in the plasma, and is present within the atherosclerotic vessels. Increased plasma levels of PAI-1 are one of the major disturbances of the hemostatic system in patients with diabetes and/or hypertension, and may have multiple interrelations with the important risk factors in the development of atherosclerosis. This study was performed to determine whether altered gene expression of PAI-1 occurs within the arterial wall, and thereby potentially contributing to the increase of cardiovascular risks associated with diabetes and/or hypertension. MATERIAL AND METHOD: The aortic vascular smooth muscle cells of the rat were exposed to 22 mM glucose, angiotensin II, and insulin increased PAI-1 mRNA expression with the use of Northern blotting were examined. Also examined were the effects of 22 mM glucose, angiotensin II and insulin on the growth of the rat's aortic smooth muscle cells by using MTT assay. RESULT: Twenty-two mM glucose treatment increased the PAI-1 mRNA expression in a time- and dose-dependent manner. Aniotensin II treatment synergistically increased the glucose-induced PAI-1 mRNA expression. In contrast, addition of insulin attenuated the increase of 22 mM glucose and angiotensin II induced PAI-1 mRNA expression. Furthermore, treatment of 22 mM glucose, angiotensin II and insulin resulted in a significant increase in cell numbers. This study demonstrated that 22 mM glucose and angiotensin II have a synergistic effect in stimulating the PAI-1 mRNA expression and in the cell growth of the rat's aortic smooth muscle cells. CONCLUSION: Elevation of glucose and angiotensin II may be important risk factors in impairing fibrinolysis and developing atherosclerosis in diabetic patients.