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.

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.

Effects of Aminoguanidine on Norepinephrine-Induced Vascular Contraction in Renovascular Hypertensive Rats / 대한신장학회잡지

BACKGROUND: It has been established that hypertension is characterized by a dysfunctional endothelium. Among the endothelial factors that cause vasorelaxation, nitric oxide has been most widely known, which is synthesized by the enzyme nitric oxide synthase. This study was aimed to evaluate the role of the inducible nitric oxide synthase in chronic two-kidney, one clip (2K1C) hypertensive rats. METHODS: 2K1C hypertension was made by clipping the left renal artery and age- matched rats received a sham treatment served as control. In vitro experiments were preformed on intact and endothelium-denuded isolated thoracic aortic rings from lipopolysaccharide (LPS)-treated rats, in the presence of aminoguanidine alone, considered to be a selective inhibitor of the inducible nitric oxide synthase and of aminoguanidine and the nonselective nitric oxide synthase inhibitor Nomega-nitro-L-arginine (L-NNA). RESULTS: LPS treatment induced a shift to the right of concentration-response curves to norepinephrine in aortic rings with or without endothelium from sham- clipped control rats, while it did not modify in 2K1C hypertensive rats. In aortic rings with endothelium, aminoguanidine caused a significant shift of the norepinephrine concentration-response curve to the left in LPS-treated control rats, but had no effect in hypertensive rats. L-NNA caused an additional shift of the concentration-response curve to norepinephrine in both control and hypertensive rats, although the magnitude was diminished in hypertensive rats. In the endothelium-denuded rings, norepinephrine-induced contractions were enhanced by aminoguanidine in LPS- treated control rats, whereas no significant changes were observed in hypertensive rats. LPS treatment inhibited the relaxation response to acetylcholine in aortic rings from control rats, while it was without effect in hypertensive rats. L-arginine caused a dose-dependent relaxation in endothelium-denuded rings from LPS-treated rats. The relaxation response to L-arginine was attenuated by aminoguanidine in control rats, but no significant changes were noted in hypertensive rats. CONCLUSION: These results provide indirect evidence for an impaired activity of the inducible nitric oxide synthase in 2K1C hypertension, although involvement of an altered activity of constitutive nitric oxide synthase in the endothelium cannot be excluded.

PGE2 Regulates Pacemaker Currents through EP2-Receptor in Cultured Interstitial Cells of Cajal from Murine Small Intestine

The interstitial cells of Cajal (ICCs) are the pacemaker cells in gastrointestinal tract and generate electrical rhythmicity in gastrointestinal muscles. Therefore, ICC may be modulated by endogenous agents such as neurotransmitter, hormones, and prostaglandins (PGs). In the present study, we investigated the effects of prostaglandins, especially PGE2, on pacemaker currents in cultured ICCs from murine small intestine by using whole-cell patch clamp techniques. ICCs generated spontaneous slow waves under voltage-clamp conditions and showed a mean amplitude of -452+/-39 pA and frequency of 18+/-2 cycles/min (n=6). Treatments of the cells with PGE2 (1muM) decreased both the frequency and amplitude of the pacemaker currents and increased the resting currents in the outward direction. PGE2 had only inhibitory effects on pacemaker currents and this inhibitory effect was dose-dependent. For characterization of specific membrane EP receptor subtypes, involved in the effects of PGE2 on pacemaker currents in ICCs, EP receptor agonists were used: Butaprost (1muM), EP2 receptor agonist, reduced the spontaneous inward current frequency and amplitude in cultured ICCs (n=5). However sulprostone (1muM), a mixed EP1 and EP3 agonist, had no effects on the frequency, amplitude and resting currents of pacemaker currents (n=5). SQ-22536 (an inhibitor of adenylate cyclase; 100muM) and ODQ (an inhibitor of guanylate cyclase; 100muM) had no effects on PGE2 actions of pacemaker currents. These observations indicate that PGE2 alter directly the pacemaker currents in ICCs, and that the PGE2 receptor subtypes involved are the EP2 receptor, independent of cyclic AMP- and GMP-dependent pathway.

Influence of Vascular Endothelium in Contraction Induced by Phorbol Ester in Renal Hypertensive Rats

BACKGROUND AND OBJECTIVES: The vascular endothelium plays an important role in circulation, by modulating the contractile responses of the arterial smooth muscle. This study was aimed at investigating the possible role of the endothelium in the contractile response to phorbol 12, 13-dibutyrate (PDB) in chronic two-kidney, one clip (2K1C) hypertensive rats. MATERIALS AND METHODS: 2K1C hypertension was induced by clipping the left renal artery of the study rats, with 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: The PDB showed a dose-dependent contraction, with larger responses in the 2K1C hypertensive than the sham-clipped control rats. Nw-nitro-L-arginine (L-NNA) and methylene blue (MB) induced an increase in the tension in the presence of PDB, and the potentiating effects of L-NNA or MB were attenuated in the 2K1C rats as compared to the controls. Staurosporine, an inhibitor of protein kinase C, completely inhibited the contractile response to PDB, as well as enhancing the effects of L-NNA and MB. Removal of the endothelium abolished the contractile responses to L-NNA and MB in both the 2K1C and control rats. The relaxation responses to acetylcholine in the aortic rings precontracted with PDB were also attenuated in the 2K1C rats, and L-NNA prevented the effect of the acetylc-holine-induced relaxation. Indomethacin, glibenclamide and iberiotoxin did not affect the PDB responses in both the 2K1C and control rats. CONCLUSION: These results indicate the endothelium plays an inhibitory role against PDB-induced contraction in rat aortae, by releasing nitric oxide, and the inhibitory role of the endothelium is impaired in 2K1C renal hypertension.

Role of Tyrosine Kinases in Norepinephrine-Induced Vascular Contraction in Renal Hypertensive Rats

BACKGROUND AND OBJECTIVES: Protein tyrosine kinases appear to be involved in the signal transduction mechanisms, which result in vascular smooth muscle contraction, as well those required in cell growth. The present study was conducted to examine the role of tyrosine kinases in the norepinephrine-induced vascular smooth muscle contraction of isolated aortae from two-kidney, one clip (2K1C) hypertensive rats. MATERIALS AND METHODS: 2K1C hypertension was made by clipping the left renal artery of the rats, with age-matched rats receiving a sham treatment serving as controls. Thoracic aortae denuded of endothelium were mounted in tissue baths to measure the isometric tension. RESULTS: The putative tyrosine kinase inhibitors, genistein and tyrphostin 25, significantly inhibited the contractile responses of the aorta to norepinephrine in the control rats, but not in the 2K1C rats. The protein tyrosine phosphatase inhibitor, sodium orthovanadate, selectively potentiated the contractile response to norepinephrine, but only in the controls. Genistein, tyrphostin 25 and sodium orthovanadate did not affect KCl-induced vascular contractions in either the 2K1C or the controls. The vascular contraction elicited by phorbol 12, 13 dibutyrate, in the presence and absence of genistein, did not alter in either the 2K1C or the controls. CONCLUSION: These findings indicate that protein tyrosine kinases participate in the norepinephrine-induced contraction of rat aortic smooth muscle, where the role is attenuated in 2K1C renal hypertension.

Inwardly Rectifying K+ Currents in Gastric Myocytes of Guinea-pig

To identify the presence of inwardly rectifying K+ channels and its characteristics, membrane currents were measured using a whole-cell patch clamp from isolated gastric myocytes of guinea-pig. Change of external K+ concentration from 5 to 90 mM induced an inward current at a holding potential of 80 mV. The high K+-induced inward current was blocked by Ba2+ and Cs+, but not by glibenclamide. With 90 mM K+ in bath, the Ba2+- and Cs+-sensitive currents showed strong inward rectification. Ten mM TEA weakly blocked the inward current only at potentials more negative than 50 mV. With 90 mM K+ in bath, hyperpolarizing step pulses from 10 mV induced inward currents, which were inactivated at potentials more negative than 70 mV. Reduction of external K+ to 60 mM decreased the amplitudes of the currents and shifted the reversal potential to more negative potential. The inactivation of inward K+ current at negative clamp voltage was not affected by removing external Na . These results suggest that the inwardly rectifying K+ channels may exist in gastric smooth muscle.

Altered Resting Nitric Oxide Vasodilator Tone in Two-Kidney, One Clip Rats / 대한신장학회잡지

Endogenous nitric oxide(NO) plays an important role in the regulation of blood pressure. It has been known that the evoked NO-dependent dilator system may be impaired in various hypertensive models. The effects of NG-nitro-L-arginine(L-NNA), lipopolysaccharide(LPS) and tempol on mean arterial pressure(MAP) and the effects of L-NNA on isolated aorta tone were studied in order to elucidate potential alterations in resting vasodilator tone of NO in two-kidney, one clip(2K1C) hypertension. Plasma nitrite/nitrate levels were measured by colorimetric assay, and the expression of endothelial and inducible NO synthases(eNOS, iNOS) was determined by Western blot analysis. L-NNA caused an increase of MAP, while LPS produced a hypotensive effect in both 2K1C and control rats. The magnitude of the pressor or depressor response to L-NNA and LPS was comparable in the two groups. Tempol induced a sustained decrease in MAP in 2K1C rats, while it had no effects on MAP in control rats. Plasma concentrations of NO metabolites were significantly increased following the LPS-treatment in both 2K1C and control rats, while they were not affected by tempol-treatment. In endothelium-intact aortic rings precontracted with 25 mM KCl, L-NNA caused a dose-dependent contraction. The magnitude of the maximal contraction was attenuated in 2K1C rats as compared with control. An inhibition of contractile responses to L-NNA in the hypertensive group was also shown in rubbed rings, although the magnitude of contractions was markedly reduced. The vascular expression of both eNOS and iNOS was significantly decreased in 2K1C rats as compared with control. These results indicate that 2K1C hypertension is associated with a reduced basal vasodilator tone of NO and a decrease in the vascular expression of NOS isozymes.

Altered Endothelial Modulation of Vasoconstriction in Chronic Two-Kidney, One Clip Hypertensive Rats / 대한신장학회잡지

It is well known that the endothelium plays an important role in the circulation by modulating contractile responses of vascular smooth muscle. This study was designed to investigate the alterations and the mechanisms of endothelial modulation in chronic 2-kidney, 1 clip(2K1C) hypertensive rats. 2K1C hypertension was made by clipping the left renal artery and age-matched control rats received a sham treatment. Aortic rings were mounted in tissue baths for measurement of isometric tension. In rings with endothelium, norepinephrine evoked concentration-dependent contraction. Endothelium removal markedly enhanced the contraction, and the responses were less pronounced in 2K1C rats than control rats. Similar fashion of the contractions by endothelium removal was observed with norepinephrine and the alpha1 drenoceptor agonist phenylephrine in control rats, while phenylephrine did not alter the contraction by endothelium removal in 2K1C rats. The alpha2 drenoceptor agonist clonidine also greatly enhanced the contraction after endothelium removal, however the endothelial inhibition was still shown in 2K1C rats. In contrast to norepinephrine-induced contractions, the enhancement of serotonin-or prostaglandin F2alpha - induced contractions after endothelium removal was small and similar in 2K1C and control rats. NG-nitro-L-arginine methyl ester enhanced the contraction induced by agonists in aortic rings with endothelium, which was similar to the response in rings without endothelium. The relaxation response to acetylcholine was attenuated in 2K1C rats, while the response to sodium nitroprusside remained unaltered. These results indicate the endothelium plays an inhibitory role against contractions in rat aorta by releasing nitric oxide, but the characteristics of the endothelial inhibition are not identical against various agonists. The negative endothelial modulation is more pronounced during alpha1 and alpha2 renoceptor- mediated contractions than during contractions mediated by other receptors. In addition, the inhibitory role of the endothelium against alpha1 drenoceptor agonist-induced contraction is impaired in 2K1C renal hypertension.