Direct vascular actions of quercetin in aorta from renal hypertensive rats

BACKGROUND: Chronic treatment with the dietary flavonoid quercetin is known to lower blood pressure and restore endothelial dysfunction in animal models of hypertension. This study investigated the direct effects of quercetin on vascular response in chronic 2-kidney, 1-clip (2K1C) renal hypertensive rats. The effects of antioxidant vitamin ascorbic acid on the vasoreactivity were also examined. METHODS: 2K1C renal hypertension was induced by clipping the left renal artery; age-matched rats that received sham treatment served as controls. Thoracic aortae were mounted in tissue baths for the measurement of isometric tension. RESULTS: Relaxant responses to acetylcholine were significantly attenuated in 2K1C rats in comparison with sham rats. Quercetin or ascorbic acid augmented acetylcholine-induced relaxation in 2K1C rats, whereas no significant differences were noted in sham rats. The relaxation response to sodium nitroprusside was comparable between 2K1C and sham rats, and sodium nitroprusside-induced relaxation was not altered by quercetin or ascorbic acid in either group. The contractile response to phenylephrine was significantly enhanced in 2K1C rats compared with sham rats. Phenylephrine-induced contraction was inhibited by pretreatment with quercetin or ascorbic acid in 2K1C rats, whereas neither chemical affected responses in sham rats. N(w)-nitro-L-arginine methyl ester markedly augmented the contractile response to phenylephrine in sham rats, whereas no significant differences were observed in 2K1C rats. Quercetin or ascorbic acid did not affect phenylephrine-induced contraction in the presence of N(w)-nitro-L-arginine methyl ester in either 2K1C or sham rats. CONCLUSION: Acute exposure to quercetin appears to improve endothelium-dependent relaxation and inhibit the contractile response, similar to the effect of ascorbic acid in 2K1C hypertension. These results partially explain the vascular beneficial effects of quercetin in renal hypertension.

Effects of oxidative stress on endothelial modulation of contractions in aorta from renal hypertensive rats

BACKGROUND: Endothelial dysfunction is linked to exaggerated production of superoxide anions. This study was conducted to examine the effects of oxidative stress on endothelial modulation of contractions in chronic two-kidney, one-clip (2K1C) renal hypertensive rats. METHODS: The 2K1C hypertension was induced by clipping the left renal artery; age-matched rats receiving sham treatment served as controls. Thoracic aortae were isolated and mounted in tissue baths for measurement of isometric tension. RESULTS: Norepinephrine-induced contraction was augmented by the removal of the endothelium, which was more pronounced in sham rats than in 2K1C rats. Nomega-nitro-L-arginine methyl ester, an inhibitor of nitric oxide production, had a similar augmenting effect. Vitamin C inhibited the contraction in aortic rings with intact endothelium from 2K1C rats but not from sham rats. The contraction was also suppressed by treatment with diphenyleneiodonium or apocynin, inhibitors of nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide phosphate (NADH/NADPH) oxidase, in the aortae with intact endothelium from 2K1C rats but not in those from sham rats. Superoxide anions generated by xanthine oxidase/hypoxanthine enhanced the contraction in the aortae with intact endothelium from sham rats, but had no effect in 2K1C rats. Enhanced contractile responses to norepinephrine by xanthine oxidase/hypoxanthine in sham rats were reversed by vitamin C. CONCLUSION: These results suggest that the effect on endothelial modulation of endothelium-derived nitric oxide is impaired in 2K1C hypertension. The impairment is, at least in part, related to increased production of superoxide anions by NADH/NADPH oxidase.

Mechanisms of phytoestrogen biochanin A-induced vasorelaxation in renovascular hypertensive rats

BACKGROUND: The plant-derived estrogen biochanin A is known to cause vasodilation, but its mechanism of action in hypertension remains unclear. This study was undertaken to investigate the effects and mechanisms of biochanin A on the thoracic aorta in two-kidney, one clip (2K1C) renovascular hypertensive rats. METHODS: Hypertension was induced by clipping the left renal artery, and control age-matched rats were sham treated. Thoracic aortae were mounted in tissue baths to measure isometric tension. RESULTS: Biochanin A caused concentration-dependent relaxation in aortic rings from 2K1C hypertensive and sham-treated rats, which was greater in 2K1C rats than in sham rats. Biochanin A-induced relaxation was significantly attenuated by removing the endothelium in aortic rings from 2K1C rats, but not in sham rats. Nomega-Nitro-L-arginine methylester, a nitric oxide synthase inhibitor, or indomethacin, a cyclooxygenase inhibitor, did not affect the biochanin A-induced relaxation in aortic rings from 2K1C and sham rats. By contrast, treatment with glibenclamide, a selective inhibitor of adenosine triphosphate-sensitive K+ channels, ortetraethy-lammonium, an inhibitor of Ca2+-activated K+ channels, significantly reduced biochanin A-induced relaxation in aortic rings from both groups. However, 4-aminopyridine, a selective inhibitor of voltage-dependent K+ channels, inhibited the relaxation induced by biochanin A in 2K1C rats, whereas no significant differences were observed in sham rats. CONCLUSION: These results suggest that the enhanced relaxation caused by biochanin A in aortic rings from hypertensive rats is endothelium dependent. Vascular smooth muscle K+ channels may be involved in biochanin A-induced relaxation in aortae from hypertensive and normotensive rats. In addition, an endothelium-derived activation of voltage-dependent K+ channels contributes, at least in part, to the relaxant effect of biochanin A in renovascular hypertension.

Endothelium-dependent vasodilation by ferulic acid in aorta from chronic renal hypertensive rats

BACKGROUND: Ferulic acid (FA) is a naturally occurring nutritional compound. Although it has been shown to have antihypertensive effects, its effects on vascular function have not been intensively established. The aim of this study was to assess the vasoreactivity of FA in chronic two-kidney, one-clip (2K1C) renal hypertensive rats. METHODS: Hypertension was induced in 2K1C rats by clipping the left renal artery and age-matched rats that received a sham treatment served as a control. Thoracic aortas were mounted in tissue baths to measure isometric tension. The effects of FA on vasodilatory responses were evaluated based on contractile responses induced by phenylephrine in the aortic rings obtained from both 2K1C and sham rats. Basal nitric oxide (NO) bioavailability in the aorta was determined by the contractile response induced by NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME). RESULTS: FA induced concentration-dependent relaxation responses which were greater in 2K1C hypertensive rats than in sham-clipped control rats. This relaxation induced by FA was partially blocked by the removal of endothelium or by pretreating with L-NAME. L-NAME-induced contractile responses were augmented by FA in 2K1C rats, while no significant differences were noted in sham rats. FA improved acetylcholine-induced endothelium-dependent vasodilation in 2K1C rats, but not in sham rats. The simultaneous addition of hydroxyhydroquinone significantly inhibited the increase in acetylcholine-induced vasodilation by FA. CONCLUSION: These results suggest that FA restores endothelial function by altering the bioavailability of NO in 2K1C hypertensive rats. The results explain, in part, the mechanism underlying the vascular effects of FA in chronic renal hypertension.

Direct Vascular Actions of Indapamide in Aorta from Renal Hypertensive Rats / 대한신장학회지

PURPOSE: Thiazide diuretics exert their hypotensive efficacy through a combined vasodilator and diuretic effect. The present study was conducted to assess the inhibitory effect of thiazide diuretic, hydrochlorothiazide, and the thiazide-like diuretics, indapamide and chlorthalidone on contractile responses to norepinephrine and arginine vasopressin in aortic rings from 2K1C renal hypertensive and sham-clipped normotensive rats. METHODS: 2K1C hypertension was made by clipping the left renal artery and age-matched control rats received a sham treatment. Changes in the tension of aortic ring preparations were measured isometrically. RESULTS: Indapamide inhibits the contractile responses to norepinephrine and vasopressin in aortic rings from 2K1C rats, while it did not modify in control rats. The inhibitory effect of indapamide was abolished by endothelium removal. Hydrochlorothiazide or chlorthalidone did not affect the vasoconstriction induced by norepinephrine and vasopressin either in sham or in 2K1C hypertensive rats. CONCLUSION: These results suggest that indapamide inhibits the contractile responses to norepinephrine and vasopressin via an endothelium-dependent mechanism in 2K1C renal hypertension.

Interplay of Hydrogen Sulfide and Nitric Oxide on the Pacemaker Activity of Interstitial Cells of Cajal from Mouse Small Intestine / 전남의대학술지

We studied whether nitric oxide (NO) and hydrogen sulfide (H2S) have an interaction on the pacemaker activities of interstitial cells of Cajal (ICC) from the mouse small intestine. The actions of NO and H2S on pacemaker activities were investigated by using the whole-cell patch-clamp technique and intracellular Ca2+ analysis at 30degrees C in cultured mouse ICC. Exogenously applied (+/-)-S-nitroso-N-acetylpenicillamine (SNAP), an NO donor, or sodium hydrogen sulfide (NaHS), a donor of H2S, showed no influence on pacemaker activity (potentials and currents) in ICC at low concentrations (10 microM SNAP and 100 microM NaHS), but SNAP or NaHS completely inhibited pacemaker amplitude and pacemaker frequency with increases in the resting currents in the outward direction at high concentrations (SNAP 100 microM and NaHS 1 mM). Co-treatment with 10 microM SNAP plus 100 microM NaHS also inhibited pacemaker amplitude and pacemaker frequency with increases in the resting currents in the outward direction. ODQ, a guanylate cyclase inhibitor, or glibenclamide, an ATP-sensitive K+ channel inhibitor, blocked the SNAP+NaHS-induced inhibition of pacemaker currents in ICC. Also, we found that SNAP+NaHS inhibited the spontaneous intracellular Ca2+ ([Ca2+]i) oscillations in cultured ICC. In conclusion, this study describes the enhanced inhibitory effects of NO plus H2S on ICC in the mouse small intestine. NO+H2S inhibited the pacemaker activity of ICC by modulating intracellular Ca2+. These results may be evidence of a physiological interaction of NO and H2S in ICC for modulating gastrointestinal motility.

5-Hydroxytryptamine Generates Tonic Inward Currents on Pacemaker Activity of Interstitial Cells of Cajal from Mouse Small Intestine

In this study we determined whether or not 5-hydroxytryptamine (5-HT) has an effect on the pacemaker activities of interstitial cells of Cajal (ICC) from the mouse small intestine. The actions of 5-HT on pacemaker activities were investigated using a whole-cell patch-clamp technique, intracellular Ca2+ ([Ca2+]i) analysis, and RT-PCR in ICC. Exogenously-treated 5-HT showed tonic inward currents on pacemaker currents in ICC under the voltage-clamp mode in a dose-dependent manner. Based on RT-PCR results, we found the existence of 5-HT2B, 3, 4, and 7 receptors in ICC. However, SDZ 205557 (a 5-HT4 receptor antagonist), SB 269970 (a 5-HT7 receptor antagonist), 3-tropanylindole - 3 - carboxylate methiodide (3-TCM; a 5-HT3 antagonist) blocked the 5-HT-induced action on pacemaker activity, but not SB 204741 (a 5-HT2B receptor antagonist). Based on [Ca2+]i analysis, we found that 5-HT increased the intensity of [Ca2+]i. The treatment of PD 98059 or JNK II inhibitor blocked the 5-HT-induced action on pacemaker activity of ICC, but not SB 203580. In summary, these results suggest that 5-HT can modulate pacemaker activity through 5-HT3, 4, and 7 receptors via [Ca2+]i mobilization and regulation of mitogen-activated protein kinases.

Interplay of Hydrogen Sulfide and Nitric Oxide on the Pacemaker Activity of Interstitial Cells of Cajal from Mouse Small Intestine / 전남의대학술지

We studied whether nitric oxide (NO) and hydrogen sulfide (H2S) have an interaction on the pacemaker activities of interstitial cells of Cajal (ICC) from the mouse small intestine. The actions of NO and H2S on pacemaker activities were investigated by using the whole-cell patch-clamp technique and intracellular Ca2+ analysis at 30degrees C in cultured mouse ICC. Exogenously applied (+/-)-S-nitroso-N-acetylpenicillamine (SNAP), an NO donor, or sodium hydrogen sulfide (NaHS), a donor of H2S, showed no influence on pacemaker activity (potentials and currents) in ICC at low concentrations (10 microM SNAP and 100 microM NaHS), but SNAP or NaHS completely inhibited pacemaker amplitude and pacemaker frequency with increases in the resting currents in the outward direction at high concentrations (SNAP 100 microM and NaHS 1 mM). Co-treatment with 10 microM SNAP plus 100 microM NaHS also inhibited pacemaker amplitude and pacemaker frequency with increases in the resting currents in the outward direction. ODQ, a guanylate cyclase inhibitor, or glibenclamide, an ATP-sensitive K+ channel inhibitor, blocked the SNAP+NaHS-induced inhibition of pacemaker currents in ICC. Also, we found that SNAP+NaHS inhibited the spontaneous intracellular Ca2+ ([Ca2+]i) oscillations in cultured ICC. In conclusion, this study describes the enhanced inhibitory effects of NO plus H2S on ICC in the mouse small intestine. NO+H2S inhibited the pacemaker activity of ICC by modulating intracellular Ca2+. These results may be evidence of a physiological interaction of NO and H2S in ICC for modulating gastrointestinal motility.

The Inhibitory Effects of Hydrogen Sulfide on Pacemaker Activity of Interstitial Cells of Cajal from Mouse Small Intestine

In this study, we studied whether hydrogen sulfide (H2S) has an effect on the pacemaker activity of interstitial cells of Cajal (ICC), in the small intestine of mice. The actions of H2S on pacemaker activity were investigated using whole-cell patch-clamp technique, intracellular Ca2+ analysis at 30degrees C and RT-PCR in cultured mouse intestinal ICC. Exogenously applied sodium hydrogen sulfide (NaHS), a donor of hydrogen sulfide, caused a slight tonic inward current on pacemaker activity in ICC at low concentrations (50 and 100 micrometer), but at high concentration (500 micrometer and 1 mM) it seemed to cause light tonic inward currents and then inhibited pacemaker amplitude and pacemaker frequency, and also an increase in the resting currents in the outward direction. Glibenclamide or other potassium channel blockers (TEA, BaCl2, apamin or 4-aminopydirine) did not have an effect on NaHS-induced action in ICC. The exogenous application of carbonilcyanide p-triflouromethoxyphenylhydrazone (FCCP) and thapsigargin also inhibited the pacemaker activity of ICC as NaHS. Also, we found NaHS inhibited the spontaneous intracellular Ca2+ ([Ca2+]i) oscillations in cultured ICC. In doing an RT-PCR experiment, we found that ICC enriched population lacked mRNA for both CSE and CBS, but was prominently detected in unsorted muscle. In conclusion, H2S inhibited the pacemaker activity of ICC by modulating intracellular Ca2+. These results can serve as evidence of the physiological action of H2S as acting on the ICC in gastrointestinal (GI) motility.

The Role of Oxygen-Derived Free Radicals in Vascular Relaxations to Pinacidil in Renal Hypertensive Rats / 대한신장학회지

PURPOSE: Evidence has emerged that oxygen-derived free radicals may induce vascular relaxations via ATP-sensitive K+ (K(ATP)) channels and the level of free radicals is increased in animal models of hypertension. The present study was conducted to determine whether relaxations to an K(ATP) channel opener, pinacidil, are increased in the aorta from two-kidney, one clip (2K1C) hypertensive rats and whether free radial scavengers reduce these relaxations. METHODS: 2K1C hypertension was induced by clipping the left renal artery and age-matched control rats received a sham treatment. Rings of aortae without endothelium were suspended for isometric force recording. RESULTS: Relaxations to pinacidil (10(-8) to 10(-5) M), which are abolished by glibenclamide (10(-5) M), were augmented in the aorta from 2K1C rats, compared to those from control rats. In the aorta from 2K1C rats, catalase (1,200 U/mL), but neither superoxide dismutase (150 U/mL) nor deferoxamine (10(-4) M), reduced relaxations to pinacidil, whereas in the aorta from control rats, the free radical scavengers did not affect these relaxations. CONCLUSION: These results suggest that in 2K1C hypertension, vasorelaxation to an KATP channel opener is augmented and that hydrogen peroxide in smooth muscle cells may partly contribute to these relaxations.

Modulation of Baroreflexes in Hypertensive Rats / 대한신장학회지

PURPOSE: Baroreceptor reflex regulation has been shown to reset towards a higher blood pressure level. This study was designed to assess alterations of chronotropic baroreflexes in two-kidney, one clip (2K1C) and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. METHODS: Arterial pressure and heart rate (HR) were monitored continuously during intravenous infusions of phenylephrine or sodium nitroprusside. Ensuing reflex HR responses during each drug infusion were determined in two ways: (a) at 10 s intervals (time analysis), and (b) with every 10 mmHg change in pressure (pressure analysis). RESULTS: Both pressor and depressor responses produced by phenylephrine or sodium nitroprusside were comparable between normotensive and hypertensive rats. Both reflex tachycardia and bradycardia were attenuated in 2K1C hypertensive rats as compared with normotensive rats, whereas no significant differences were shown in DOCA-salt hypertensive rats. CONCLUSION: These results indicate that chronotropic baroreflexes are impaired in 2K1C hypertensive rats, but not in DOCA-salt hypertensive rats.

Effects of Atrial Natriuretic Peptide on the Arterial Basal Tone in Renovascular Hypertensive Rats / 대한신장학회지

PURPOSE: Hypertension may be involved an alteration of intrinsic basal tone in vascular smooth muscle. The purpose of this study was to investigate the vasorelaxant effect of atrial natriuretic peptide (ANP) on isolated non-contracted aorta from two-kidney, one clip (2K1C) renovascular hypertensive rats. METHODS: 2K1C hypertension was induced by clipping the left renal artery and were used 6 weeks later. Age-matched rats receiving a sham treatment, which served as controls. The thoracic aortae were mounted in tissue baths to measure the isometric tension. RESULTS: ANP diminished basal tone in previously unstimulated thoracic aortic rings from 2K1C hypertensive rats, while it had no effect in the control rats. Endothelial destruction potentiated the vasorelaxant effect of ANP on basal tone in 2K1C rats. A similar potentiation of the ANP response was observed by pre-treatment with N omega-nitro-L-arginine methyl ester (L-NAME) or methylene blue in aortic rings with endothelium. Treatment with calcium-free Krebs decreased basal tone and abolished ANPresponse. These effects were observed only in aortic rings from 2K1C rats. Similarly, staurosporine and calphostin C, inhibitors of protein kinase C (PKC), lowered basal tone and abolished ANP-response in hypertensive rats. CONCLUSION: These results demonstrate that ANP has a vasorelaxant effect on basal tone in 2K1C renovascular hypertension. Inhibition of ANP effects on basal tone by calcium-free Krebs and PKC antagonists suggests that altered Ca2+ -active tone is involved in hypertension, that modifies the response of vascular smooth muscle to the ANP.

(-)-Epigallocatechin Gallate Inhibits the Pacemaker Activity of Interstitial Cells of Cajal of Mouse Small Intestine

The effects of (-)-epigallocatechin gallate (EGCG) on pacemaker activities of cultured interstitial cells of Cajal (ICC) from murine small intestine were investigated using whole-cell patch-clamp technique at 30degrees C and Ca2+ image analysis. ICC generated spontaneous pacemaker currents at a holding potential of -70 mV. The treatment of ICC with EGCG resulted in a dose-dependent decrease in the frequency and amplitude of pacemaker currents. SQ-22536, an adenylate cyclase inhibitor, and ODQ, a guanylate cyclase inhibitor, did not inhibit the effects of EGCG. EGCG-induced effects on pacemaker currents were not inhibited by glibenclamide, an ATP-sensitive K+ channel blocker and TEA, a Ca2+-activated K+ channel blocker. Also, we found that EGCG inhibited the spontaneous [Ca2+]i oscillations in cultured ICC. In conclusion, EGCG inhibited the pacemaker activity of ICC and reduced [Ca2+]i oscillations by cAMP-, cGMP-, ATP-sensitive K+channel-independent manner.

Involvement of Thromboxane A2 in the Modulation of Pacemaker Activity of Interstitial Cells of Cajal of Mouse Intestine

Although many studies show that thromboxane A2 (TXA2) has the action of gastrointestinal (GI) motility using GI muscle cells and tissue, there are no reports on the effects of TXA2 on interstitial cells of Cajal (ICC) that function as pacemaker cells in GI tract. So, we studied the modulation of pacemaker activities by TXA2 in ICC with whole cell patch-clamp technique. Externally applied TXA2 (5 micrometer) produced membrane depolarization in current-clamp mode and increased tonic inward pacemaker currents in voltage-clamp mode. The tonic inward currents by TXA2 were inhibited by intracellular application of GDP-beta-S. The pretreatment of ICC with Ca2+ free solution and thapsigargin, a Ca2+-ATPase inhibitor in endoplasmic reticulum, abolished the generation of pacemaker currents and suppressed the TXA2-induced tonic inward currents. However, chelerythrine or calphostin C, protein kinase C inhibitors, did not block the TXA2-induced effects on pacemaker currents. These results suggest that TXA2 can regulate intestinal motility through the modulation of ICC pacemaker activities. This modulation of pacemaker activities by TXA2 may occur by the activation of G protein and PKC independent pathway via extra and intracellular Ca2+ modulation.

Inhibition of Pacemaker Activity of Interstitial Cells of Cajal by Hydrogen Peroxide via Activating ATP-sensitive K(+) Channels

To investigate whether hydrogen peroxide (H2O2) affects intestinal motility, pacemaker currents and membrane potential were recorded in cultured interstitial cells of Cajal (ICC) from murine small intestine by using a whole-cell patch clamp. In whole cell patch technique at 30 degress C, ICC generated spontaneous pacemaker potential under current clamp mode (I=0) and inward currents (pacemaker currents) under voltage clamp mode at a holding potential of -70 mV. When ICC were treated with H2O2 in ICC, H2O2 hyperpolarized the membrane potential under currents clamp mode and decreased both the frequency and amplitude of pacemaker currents and increased the resting currents in outward direction under voltage clamp mode. Also, H2O2 inhibited the pacemaker currents in a dose-dependent manner. Because the properties of H2O2 action on pacemaker currents were same as the effects of pinacidil (ATP-sensitive K+ channels opener), we tested the effects of glibenclamide (ATP-sensitive K+ channels blocker) on H2O2 action in ICC, and found that the effects of H2O2 on pacemaker currents were blocked by co- or pre-treatment of glibenclamide. These results suggest that H2O2 inhibits pacemaker currents of ICC by activating ATP-sensitive K(+) channels.

Role of KCa Channels in SNAP-Induced Relaxation of Aorta from Renal Hypertensive Rats / 대한신장학회지

PURPOSE: S-nitroso-N-acetylpenicillamine (SNAP), a nitric oxide (NO) donor, is thought to relax vascular smooth muscle by stimulation of soluble guanylate cyclase, accumulation of its product cyclic GMP (cGMP) level. Evidence has emerged that NO-induced vasodilatation is also mediated by stimulating Ca2+-activated K+ (KCa) channels directly or indirectly through cGMP. The aim of the present study was to investigate possible involvement or alteration of KCa channels in the mechanism of vasodilation induced by SNAP in two-kidney, one-clip (2K1C) hypertensive rats. METHODS: 2K1C hypertension was made by clipping the left renal artery and age-matched control rats received a sham treatment. Using rings prepared from thoracic aortae, we studied changes in isometric tension of the rings in response to SNAP to evaluate effects of a soluble guanylate cyclase inhibitor methylene blue (MB), and a specific blocker of KCa channel iberiotoxin (ITX). RESULTS: Aortic rings from 2K1C hypertensive and sham-clipped control rats precontracted with phenylephrine showed similar relaxation to SNAP. MB markedly suppressed the SNAP-induced relaxation in both groups, leaving about 30% of MB-resistant relaxation. ITX nearly completely eliminated the MB-resistant relaxation in control rats, but it did not affect 2K1C rats. CONCLUSION: These results suggest that SNAP-induced vasorelaxation is mediated through cGMP- dependent and cGMP-independent KCa channel involving mechanisms, the latter may be altered in 2K1C renal hypertension.

Altered Dilator Responses to Heptanol and Octanol in Aorta from Renal Hypertensive Rats / 대한신장학회잡지

BACKGROUND: Cells rely on gap junctions for intercellular communication, which is important for growth and contractility. The present study was conducted to test the hypothesis that contractile responses in aortic rings from two-kidney, one clip (2K1C) hypertensive rats are more dependent on gap junctional communication compared to those from normotensive rats. METHODS: 2K1C hypertension was induced by clipping the left renal artery and age-matched rats received a sham operation. Heptanol and octanol were used as inhibitors of gap junctional activity. RESULTS: The contraction induced by phenylephrine or KCl was completely reversed by either heptanol or octanol, and the relaxant response to inhibitors was more enhanced in 2K1C hypertensive rats compared to sham-operated rats. Vessels from hypertensive rats also relaxed more to nifedipine when precontracted with KCl, although it did not differ in aortic segments contracted with phenylephrine in between normotensive and hypertensive rats. CONCLUSION: These results suggest that gap junctional communication and voltage-operated calcium channels are differentially regulated in 2K1C renal hypertension.

Altered Dilator Responses to Heptanol and Octanol in Aorta from Renal Hypertensive Rats / 대한신장학회잡지

BACKGROUND: Cells rely on gap junctions for intercellular communication, which is important for growth and contractility. The present study was conducted to test the hypothesis that contractile responses in aortic rings from two-kidney, one clip (2K1C) hypertensive rats are more dependent on gap junctional communication compared to those from normotensive rats. METHODS: 2K1C hypertension was induced by clipping the left renal artery and age-matched rats received a sham operation. Heptanol and octanol were used as inhibitors of gap junctional activity. RESULTS: The contraction induced by phenylephrine or KCl was completely reversed by either heptanol or octanol, and the relaxant response to inhibitors was more enhanced in 2K1C hypertensive rats compared to sham-operated rats. Vessels from hypertensive rats also relaxed more to nifedipine when precontracted with KCl, although it did not differ in aortic segments contracted with phenylephrine in between normotensive and hypertensive rats. CONCLUSION: These results suggest that gap junctional communication and voltage-operated calcium channels are differentially regulated in 2K1C renal hypertension.

Effects of Tamoxifen on the Voltage-dependent Ionic Currents in Mouse Colonic Smooth Muscle Cells / 대한소화기학회지

BACKGROUND/AIMS: Tamoxifen is a widely used anticancer drug for breast cancer with frequent gastrointestinal side effects. Changes in gastrointestinal motility is associated with altered activities of membrane ion channels. Ion channels have important role in regulating membrane potential and cell excitability. This study was performed to investigate the effects of tamoxifen on the membrane ionic currents in colonic smooth muscle cells. METHODS: Murine colonic smooth muscle cells were isolated from the proximal colon using collagenase, and the membrane currents were recorded using a whole-cell patch clamp technique. RESULTS: Two types of voltage-dependent K+ currents were recorded (A-type and delayed rectifier K+ currents). Tamoxifen inhibited both types of voltage-dependent K+ currents in a dose-dependent manner. However, tamoxifen did not change the half-inactivation potential and the recovery time of voltage-dependent K+ currents. Chelerythrine, a protein kinase C inhibitor or phorbol 12, 13-dibutyrate, a protein kinase C activator did not affect the voltage-dependent K+ currents. Guanosine 5'-O-(2-thio-diphosphate) did not affect the tamoxifen-induced inhibition of voltage-dependent K+ currents. Tamoxifen inhibited voltage-dependent Ca2+ currents completely in whole-test ranges. CONCLUSIONS: These results suggest that tamoxifen can alter various membrane ionic currents in smooth muscle cells and cause some adverse effects on the gastrointestinal motility.

Effects of Nitric Oxide Synthesis Inhibition on the Depressor Response of Atrial Natriuretic Peptide in Rats

BACKGROUND AND OBJECTIVES: It has been suggested that nitric oxide (NO) and atrial natriuretic peptide (ANP) share a final common pathway for vascular smooth muscle relaxation. The aim of the present study was to determine the role of NO on the hypotensive and vasorelaxant effects of ANP. MATERIALS AND METHODS: Sprague-Dawley rats weighing 250-300 g each were anesthetized with thiopental (50 mg/kg IP). The femoral artery was cannulated and the arterial blood pressure and heart rate were continuously monitored in the anesthetized rats (n=19). ANP was administered into the jugular vein after L-NAME treatment. In vitro experiments were performed on intact and endothelium-denuded isolated thoracic aortic rings (n=51) in the presence of either L-NAME or methylene blue. RESULTS: Intravenous administration of ANP (5 ug/kg bolus and 0.2 ug/kg/min infusion) caused a decrease in the mean arterial pressure. L-NAME-pretreatment (1 mg/kg) suppressed the depressor response of ANP. In vitro, the ANP caused a dose-dependent relaxation, and the relaxation response to ANP was attenuated by L-NAME (10-4 M). Endothelium removal or methylene blue (10-5 M) also inhibited the ANP-induced vascular relaxation. CONCLUSION: These results suggest that the hypotensive and the vasorelaxant effect of ANP are, at least in part, NO-dependent.