The Endothelium-Dependent Nitric Oxide-cGMP Pathway

Nitric oxide (NO)-cyclic 3'-5' guanosine monophosphate (cGMP) signaling plays a critical role on smooth muscle tone, platelet activity, cardiac contractility, renal function and fluid balance, and cell growth. Studies of the 1990s established endothelium dysfunction as one of the major causes of cardiovascular diseases. Therapeutic strategies that benefit NO bioavailability have been applied in clinical medicine extensively. Basic and clinical studies of cGMP regulation through activation of soluble guanylyl cyclase (sGC) or inhibition of cyclic nucleotide phosphodiesterase type 5 (PDE5) have resulted in effective therapies for pulmonary hypertension, erectile dysfunction, and more recently benign prostatic hyperplasia. This section reviews (1) how endothelial dysfunction and NO deficiency lead to cardiovascular diseases, (2) how soluble cGMP regulation leads to beneficial effects on disorders of the circulation system, and (3) the epigenetic regulation of NO-sGC pathway components in the cardiovascular system. In conclusion, the discovery of the NO-cGMP pathway revolutionized the comprehension of pathophysiological mechanisms involved in cardiovascular and other diseases. However, considering the expression "from bench to bedside" the therapeutic alternatives targeting NO-cGMP did not immediately follow the marked biochemical and pathophysiological revolution. Some therapeutic options have been effective and released on the market for pulmonary hypertension and erectile dysfunction such as inhaled NO, PDE5 inhibitors, and recently sGC stimulators. The therapeutic armamentarium for many other disorders is expected in the near future. There are currently numerous active basic and clinical research programs in universities and industries attempting to develop novel therapies for many diseases and medical applications.

[Segmental tracheal resection and anastomosis for the treatment of cicatricial stenosis in cervical tracheal]

OBJECTIVE

To evaluate the efficacy of segmental tracheal resection with end-to-end anastomosis for cicatricial cervical tracheal stenosis.

METHODS

The clinical outcomes of 40 patients treated with tracheal resection were retrospectively reviewed. There were 28 male patients and 12 female patients with the age ranged from 6 to 64 years (mean 33.7 years). The degree of stenosis was classified according to Myer-Cotton classification as follows: grade Ⅱ (n=7), grade Ⅲ (n=22) and grade Ⅳ (n=11). The stenosis extension ranged from 1.0 to 4.3 cm (mean 2.5 cm). The causes of the stenosis were postintubation (n=33), cervical trauma (n=6) and resection of tracheal neoplasm (n=1).

RESULTS

Thirty-four(85.0%) patients were decannulated and 6 failed. Of the 6 patients failed, 4 were decannulated after reoperation with the sternohyoid myocutaneous flap or thyroid alar cartilage graft. Complications occurred in 10 patients. In 8 patients granulation tissues formed at the site of the tracheal anastomosis, which needed endoscopic resction, and in 2 patients anastomosic dehiscence occurred. No injury to recurrent laryngeal nerve or trachoesophageal fistula occurred.

CONCLUSION

Segmental tracheal resection with end-to-end anastomosis is an effective surgical method for tracheal stenosis, which has a higher successful rate for primary operation and shorter therapeutic period.

Effect of ozone treatment on deoxynivalenol and quality evaluation of ozonised wheat

Deoxynivalenol (DON) is the secondary metabolite of Fusarium graminearum, which is always found in Fusarium head blight of wheat. In this study, gaseous ozone was used to treat both DON solution and scabbed wheat to investigate the effectiveness of ozone treatment on DON degradation and the effect of ozone on the quality parameters of wheat. It was found that gaseous ozone had a significant effect on DON reduction in solution, when 10 mg l(-1) gaseous ozone was used to treat a 1 μg ml(-1) of DON solution, the degradation rate of DON was 93.6% within 30 s. Lower initial concentrations of DON solution treated with higher concentrations of ozone, and longer times showed higher DON degradation rates. Gaseous ozone was effective against DON in scabbed wheat. The degradation rate of DON increased with ozone concentration and processing time. The correlation between the time and degradation rate was y = -1.1926x(2) + 11.427x - 8.7787. In the process of ozone oxidation, a higher moisture content of wheat was more sensitive than that of lower moisture content to ozone under the same conditions. All samples were treated with different concentrations of ozone for 4 h to investigate the effect of ozone on wheat quality. No significant detrimental changes in the starch pasting properties of wheat were observed after all the samples were treated with ozone within 4 h. On the other hand, there was a slight rise in the dough development time and stability time, which meant the quality of flour improved after ozone treatment.

Nitric oxide and cyclic GMP signaling pathway as a focus for drug development

Recent progress in understanding of the nitric oxide and cGMP signaling pathway provided evidence for mechanism of action of known drugs and identified novel targets for drug development. These discoveries resulted in numerous efforts in drug and formulation discovery. Some of the most promising approaches were applied for efficient therapies of various diseases.

Diversity of endotoxin-induced nitrotyrosine formation in macrophage-endothelium-rich organs

The administration of bacterial lipopolysaccharide (LPS; endotoxin) can stimulate the development of the systemic inflammatory response syndrome, which can compromise the function of many organ systems, resulting in multiple organ failure. Activation of macrophages and cytokines by endotoxin and the subsequent formation of reactive oxygen and nitrogen species are of central pathogenic importance in various inflammatory diseases including sepsis. However, whether different tissues behave the same in pathological changes produced by LPS and what factors may affect pathological processes and protein tyrosine nitration in different organs, still remain to be evaluated. In the present study, we investigated the distribution of nitrotyrosine and other pathological changes induced by LPS in rat liver, spleen, and lung, all of which are rich in macrophages and endothelial cells. Our study revealed two important findings: first, a denitration activity in spleen white pulp might play a key role to protect the areas from nitration. Similar activity might also exist in endothelial cells of sinusoids and capillaries. Second, protein nitration might not induce significant tissue damage as shown in liver and spleen. However, inflammatory infiltration with increased formation NO* and other reactive species may result in severe tissue injury, as demonstrated in lung after LPS administration.

Down-regulation of inducible nitric-oxide synthase (NOS-2) during parasite-induced gut inflammation: a path to identify a selective NOS-2 inhibitor

Nitric oxide (NO) possesses potent anti-inflammatory properties; however, an over-production of NO will promote inflammation and induce cell and tissue dysfunction. Thus, the ability to precisely regulate NO production could prove beneficial in controlling damage. In this study, advantage was taken of the well characterized inflammatory response caused by an intestinal parasite, Trichinella spiralis, to study the relationship between intestinal inflammation and the regulation of nitric oxide synthase-type 2 (NOS-2) expression. Our study revealed that a specific gut inflammatory reaction results in inhibition of NOS-2 expression. Characteristics of this inhibition are: 1) local jejunal inflammation induced by T. spiralis systemically inhibits NOS-2 gene transcription, protein expression, and enzyme activity; 2) the inhibition blunts endotoxin-stimulated NOS-2 expression; 3) the inhibition does not extend to the expression of other isoforms of NOS, to paxillin, a housekeeper protein, or to cyclooxygenase-2, another protein induced by proinflammatory cytokines; 4) the inhibition is unlikely related to the formation of specific anti-parasite antibodies; and 5) the inhibition may involve substances other than stress-induced corticosteroids. Elucidation of such potent endogenous NOS-2 down-regulatory mechanisms could lead to the development of new strategies for the therapy of inflammatory conditions characterized by the overproduction of NO.

Cutting edge: targeted disruption of the C3a receptor gene demonstrates a novel protective anti-inflammatory role for C3a in endotoxin-shock

The complement anaphylatoxin C3a, on binding the C3aR, mediates numerous proinflammatory activities. In addition, recent in vitro studies with C3a have implicated C3aR as a possible anti-inflammatory receptor. Because of its possible dual role in modulating the inflammatory response, it is uncertain whether C3aR contributes to the pathogenesis of endotoxin shock. Here, the targeted-disruption of the C3aR in mice is reported. These mice exhibit an enhanced lethality to endotoxin shock with a pronounced gene dosage effect. In addition, the plasma concentration of IL-1beta was significantly elevated in the C3aR(-/-) mice compared with their littermates following LPS challenge. These findings demonstrate an important protective role for the C3aR in endotoxin shock and indicate that, in addition to its traditionally accepted functions in mediating inflammation, the C3aR also acts in vivo as an anti-inflammatory receptor by attenuating LPS-induced proinflammatory cytokine production.

Cellular signaling with nitric oxide and cyclic guanosine monophosphate

The understanding of the formation and biological actions of nitric oxide (NO) has grown extensively during the past two decades. With the discoveries of the biological effects of NO and nitrovasodilators on cyclic guanosine monophosphate, with the elucidation of the biochemical mechanisms of NO synthesis, and with the growing knowledge of regulation of NO synthases, the complexities of this signal transduction cascade and its participation in numerous cell signaling processes continues. NO can be recognized as an intracellular second messenger, a local substance for regulation of neighboring cells, a neurotransmitter, and probably a hormone acting at distant sites.

Nitrotyrosine formation with endotoxin-induced kidney injury detected by immunohistochemistry

The presence of nitrotyrosine in the kidney has been associated with several pathological conditions. In the present study, we investigated nitrotyrosine formation in rat kidney after animals received endotoxin for 24 h. With lipopolysaccharide (LPS) treatment, immunohistochemical data demonstrated intense nitrotyrosine staining throughout the kidney. In spite of marked nitrotyrosine formation, the architectural appearance of tubules, glomeruli, and capillaries remained intact when examined by reticulin staining. Our data suggested that the marked staining of nitrotyrosine in proximal tubular epithelial cells was in the subapical compartment where the endocytic lysosomal apparatus is located. Thus a large portion of nitrotyrosine may come from the hydrolysis of nitrated proteins that are reabsorbed by the proximal tubule during the LPS treatment. We also found the colocalization of nitric oxide synthase (NOS-1) and nitrotyrosine within the macula densa of LPS-treated rats by using a double fluorescence staining method. In renal arterial vessels, vascular endothelial cells were more strongly stained for nitrotyrosine than vascular smooth muscle cells. Control animals without LPS treatment showed much less renal staining for nitrotyrosine. The general distribution of nitrotyrosine staining in control rat renal cortex is in the proximal and convoluted tubules, whereas the endothelial cells of vasa recta are major areas of nitrotyrosine staining in inner medulla. The renal distribution of nitrotyrosine in control and LPS-treated animals suggests that protein nitration may participate in renal regulation and injury in ways that are yet to be defined.

An activity in rat tissues that modifies nitrotyrosine-containing proteins

Homogenates from rat spleen and lung could modify nitrotyrosine-containing BSA. With incubation, nitrotyrosine-containing BSA lost its epitope to a monoclonal antibody that selectively recognized nitrotyrosine-containing proteins. In the presence of protease inhibitors, the loss of the nitrotyrosine epitope occurred without protein degradation and hydrolysis. This activity was found in supernatant but not particulate fractions of spleen homogenates. The factor was heat labile, was sensitive to trypsin treatment, and was retained after passage through a membrane with a 10-kDa retention. The activity was time- and protein-concentration dependent. The activity increased about 2-fold in spleen extracts with endotoxin (bacterial lipopolysaccharide) treatment of animals, suggesting that the activity is inducible or regulatable. Other nitrotyrosine-containing proteins also served as substrates, while free nitrotyrosine and some endogenous nitrotyrosine-containing proteins in tissue extracts were poor substrates. Although the product and possible cofactors for this reaction have not yet been identified, this activity may be a "nitrotyrosine denitrase" that reverses protein nitration and, thus, decreases peroxynitrite toxicity. This activity was not observed in homogenates from rat liver or kidney, suggesting that there may also be some tissue specificity for the apparent denitrase activity.

Perivascular sensory nerve Ca2+ receptor and Ca2+-induced relaxation of isolated arteries

The present study tested two hypotheses: (1) that a receptor for extracellular Ca2+ (Ca2+ receptor [CaR]) is located in the perivascular sensory nerve system and (2) that activation of this receptor by physiological concentrations of extracellular Ca2+ results in the release of vasodilator substance that mediates Ca2+-induced relaxation. Reverse transcription-polymerase chain reaction using primers derived from rat kidney CaR cDNA sequence showed that mRNA encoding a CaR is present in dorsal root ganglia but not the mesenteric resistance artery. Western blot analysis using monoclonal anti-CaR showed that a 140-kD protein that comigrates with the parathyroid CaR is present in both the dorsal root ganglia and intact mesenteric resistance artery. Immunocytochemical analysis of whole mount preparations of mesenteric resistance arteries showed that the anti-CaR-stained perivascular nerves restricted to the adventitial layer. Biophysical analysis of mesenteric resistance arteries showed that cumulatively raising Ca2+ from 1 to 1.25 mol/L and above relaxes precontracted arteries with an ED50 value of 2.47+/-0.17 mmol/L (n=12). The relaxation is endothelium independent and is unaffected by blockade of nitric oxide synthase but is completely antagonized by acute and subacute phenolic destruction of perivascular nerves. A bioassay showed further that superfusion of Ca2+ across the adventitial surface of resistance arteries releases a diffusible vasodilator substance. Pharmacological analysis indicates that the relaxing substance is not a common sensory nerve peptide transmitter but is a phospholipase A2/cytochrome P450-derived hyperpolarizing factor that we have classified as nerve-derived hyperpolarizing factor. These data demonstrate that a CaR is expressed in the perivascular nerve network, show that raising Ca2+ from 1 to 1.25 mol/L and above causes nerve-dependent relaxation of resistance arteries, and suggest that activation of the CaR induces the release of a diffusible hyperpolarizing vasodilator. We propose that this system could serve as a molecular link between whole-animal Ca2+ balance and arterial tone.

Traumatic brain injury does not alter cerebral artery contractility

Previous studies have shown that traumatic brain injury (TBI) significantly reduces cerebral blood flow determined in vivo and reduces vascular reactivity in the pial circulation measured with cranial window preparations. We have now tested the hypothesis that TBI induces these changes by impairing intrinsic contractile activity of cerebral arteries. Anesthetized rats underwent moderate (2.2 atm) and severe (3.0 atm) midline fluid percussion TBI or sham injury following which posterior cerebral or middle cerebral arteries were isolated and isometric force generation was measured. Moderate (n = 5) and severe (n = 3) trauma had no effect on the magnitude of serotonin- or K+-induced force generation or sensitivity to serotonin in arteries isolated within 10 min of TBI. Functional disruption of the endothelium of posterior cerebral arteries isolated 10 min after moderate trauma or sham injury caused a reduction in the active tension response to serotonin that was similar in both groups. Blockade of cyclooxygenase with 5 microM indomethacin had no effect on serotonin-induced force generated by vessels with moderate trauma or in sham-treated rats. Acetylcholine induced an endothelium-dependent relaxation of posterior and middle cerebral arteries; the magnitude of the response was unaffected by moderate TBI. To determine whether prolonged in situ exposure of vessels to the traumatized cerebral milieu could reveal an alteration in intrinsic contractility, posterior cerebral arteries were isolated 30 min after TBI; again, no differences in the tension or relaxation responses were observed. It is concluded that midline fluid percussion TBI did not affect contraction or relaxation of proximal middle or posterior cerebral arteries in rats.

Agonists increase the sensitivity of contractile elements for Ca++ in pregnant rat myometrium

OBJECTIVE

The effects of agonists and guanosine 5'-triphosphate binding proteins (G proteins) on contractile properties were investigated in rat longitudinal myometrial tissues in late gestation and during delivery.

STUDY DESIGN

The effect of carbachol was examined on the intracellular Ca++ concentration in intact thin muscle strips from pregnant rat myometrium. In addition, the action of carbachol with guanosine 5'-triphosphate was examined on the Ca(++)-induced contractions in beta-escin-treated skinned strips (membrane-permeable conditions and chemical clamping of intracellular Ca++ concentrations). The effects of guanosine 5'-0-(gamma-thiotriphosphate) (a nonhydrolyzable analog of guanosine 5'-triphosphate), prostaglandin F2 alpha with guanosine 5'-triphosphate, prostaglandin E2 with guanosine 5'-triphosphate, and okadaic acid (a phosphatase inhibitor) were also examined in skinned strips.

RESULTS

In intact longitudinal rat myometrium at late gestation the maximum contractions induced by carbachol were larger than the maximum contractions induced by high K+ (118 mmol/L), whereas increases in intracellular Ca++ concentration produced by both agents were similar. In beta-escin-treated skinned myometrial strips from late gestation, 0.3 mumol/L Ca++ evoked contractions. Carbachol (10 mumol/L) plus guanosine 5'-triphosphate (10 mumol/L) enhanced the 0.3 mumol/L Ca(++)-induced contractions of skinned strips; the increase was antagonized by 1 mmol/L guanosine 5'-0-(beta-thiodiphosphate). Guanosine 5'-0-(gamma-thiotriphosphate) (0.1 to 100 mumol/L), prostaglandin F2 alpha (10 mumol/L) plus guanosine 5'-triphosphate (10 mumol/L), prostaglandin E2 (10 mumol/L) plus guanosine 5'-triphosphate (10 mumol/L), and okadaic acid (1 nmol/L) also augmented 0.3 mumol/L Ca++ contractions in skinned strips. The increases of 0.3 mumol/L Ca(++)-induced contractility by the agonists with guanosine 5'-triphosphate or guanosine 5'-0-(gamma-thiotriphosphate) were similar between late gestation and delivery.

CONCLUSION

These results suggest that agonists such as carbachol, prostaglandin F2 alpha, and prostaglandin E2 enhance the Ca(++)-induced contraction of myometrium at late gestation through G protein-mediated mechanisms. The agonist/G protein-mediated Ca(++)-sensitizing effects on contractile elements produce additional contractile force with the same amount of intracellular calcium, thus providing expelling forces for delivery of the fetuses.

1,25(OH)2D3 modulates intracellular Ca2+ and force generation in resistance arteries

The mechanism by which 1 alpha,25-dihydroxycholecalciferol [1,25(OH)2D3] enhances smooth muscle force generation was examined. Rats were injected on three mornings with 1,25(OH)2D3 (35 ng/100 g) or vehicle, and on the fourth morning mesenteric resistance arteries were isolated and used for simultaneous measurement of intracellular Ca2+ and force or myosin light chain phosphorylation. 1,25(OH)2D3 did not affect media thickness or wall-to-lumen ratio, but it increased basal intracellular Ca2+ (vehicle = 49.2 +/- 2.2 nM vs. 1,25(OH)2D3 = 65.9 +/- 4.0 nM, P < 0.05, n = 24-26 rats). 1,25(OH)2D3 enhanced the active stress and intracellular Ca2+ responses to increasing doses of norepinephrine, and the increases were normalized by verapamil (10 microM). In a second group of animals, 1,25(OH)2D3 significantly increased both basal intracellular Ca2+ and light chain phosphorylation and the active stress and Ca2+ mobilization responses to norepinephrine (10 microM). The hormone did not affect peak or steady-state light chain phosphorylation. Myofilament Ca2+ sensitivity, determined during stimulation with 2 microM norepinephrine, was depressed in vessels isolated from rats treated with 1,25(OH)2D3 [vehicle Ca2+ 50% effective dosé (ED50) = 82.7 +/- 3.8 nM vs. 1,25(OH)2D3 = 104.8 +/- 4.9 nM, P = 0.002]. We conclude that 1,25(OH)2D3 enhances resistance artery force generation by altering smooth muscle Ca2+ homeostasis, with effects on basal and verapamil-sensitive, agonist-induced Ca2+ mobilization.

Vascular actions of the calcium-regulating hormones

The vascular actions of the hormones that participate in the regulation of whole animal calcium (Ca2+) homeostasis and related factors are discussed. Parathyroid hormone (PTH) has vasodilator activity that is mediated by a specific cell membrane receptor coupled to adenylate cyclase and thus increases intracellular cAMP and lowers intracellular Ca2+. The peptide may also block voltage-sensitive Ca2+ channels. However, the general consensus is that PTH does not achieve sufficient levels in the serum to modulate vascular reactivity. Parathyroid hormone does, however, share a common receptor and N-terminal amino acid sequence homology with parathyroid hormone-related peptide (PTHrp), which has many of the properties of a locally acting vascular regulator. Exciting actions of the steroid hormone, 1,25(OH)2 vitamin D3, have recently been described which suggest that the hormone is a vascular smooth muscle-differentiating agent and promises to set the stage for learning about the long-term modulatory actions of other steroid hormones. Calcitonin has minimal vascular actions, and although CGRP is not classifiable as a Ca(2+)-regulating hormone, it is a potent vasodilator neurotransmitter. Finally, within the past 2 years there has been a ground swell of activity surrounding the existence of the extracellular Ca2+ receptor that senses changes in interstitial Ca2+. The response of the smooth muscle cell to extracellular Ca2+ is discussed in the context of this receptor.

Differential expression and effect of 1,25-dihydroxyvitamin D3 on myosin in arterial tree of rats

The hypothesis that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3, also known as calcitriol] modulates myosin expression in vascular smooth muscle was tested. Wistar-Kyoto or spontaneously hypertensive rats given intraperitoneal injections of 25 ng 1,25(OH)2D3/100 g body weight for varying periods of time showed a greater than twofold increase in aortic mRNA encoding the myosin regulatory light chain relative to 18S rRNA (P < 0.05). 1,25(OH)2D3 administration to Wistar rats caused a significant increase in the aortic content of total myosin regulatory light chain and total myosin heavy chain. The increase in myosin light chain was the result of a specific increase in expression of its smooth muscle isoform [control = 65.2 +/- 3.4% vs. 1,25(OH)2D3 = 78.7 +/- 3.6%, P = 0.020]. 1,25(OH)2D3 had no effect on total myosin light chain or heavy chain in the superior mesenteric artery. The hormone did, however, increase the proportion of the smooth muscle isoform of the light chain in this vessel [control = 81.4 +/- 2.6% vs. 1,25(OH)2D3 = 88.8 +/- 2.1%, P = 0.048]. In branch II and III mesenteric resistance arteries, 1,25(OH)2D3 significantly increased the active stress response to 10 mumol/l norepinephrine but was without effect on total myosin light chain or heavy chain content or on the relative expression of the myosin light chain isoforms [control = 94.0 +/- 1.4% vs. 1,25(OH)2D3 = 95.8 +/- 1.1%, P = 0.33].(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of resistance artery force generation by extracellular Ca2+

We tested the hypothesis that increasing extracellular Ca2+ (Cao) over a physiological concentration range depresses vascular smooth muscle force generation by altering the intracellular Ca2+ (Cai)-force relationship. Mesenteric resistance arteries were isolated from Wistar rats; Cai and isometric force were measured using a fura-based method and wire myography. Vessels were depleted of releasable Cai by repeated contraction with norepinephrine; Cao was then cumulatively added back from 0.025-2.5 mM in the presence of an agonist. With norepinephrine, serotonin, prostaglandin F2 alpha, and K+, Cao from 0.025 to 0.8 mM induced a graded increase in Cai and active stress. With the receptor agonists but not K+ raising Cao from 0.8 to 1.6 mM and from 1.6 to 2.5 mM decreased active stress to 82 +/- 6 and 54 +/- 6% of maximum, respectively, P < 0.05. Although there was a transient decrease in Cai in response to both 1.6 and 2.5 mM Cao, steady-state Cai only decreased significantly in response to 2.5 mM Cao (85 +/- 3% of maximum). Inhibition of the sarcoplasmic reticulum Ca(2+)-adenosinetriphosphatase with 1 microM thapsigargin had no effect on the decrease in force induced by high Ca2+. The decrease in active stress induced by 1.6 and 2.5 mM Cao was inhibited by Ca2+ channel antagonists and by blockade of Ca(2+)-activated K+ channels with charybdotoxin (with 1.6 mM Cao, control tension = 67 +/- 10% of maximum vs. charybdotoxin = 99.2 +/- 1%, P < 0.05; n = 9).(ABSTRACT TRUNCATED AT 250 WORDS)

Myofilament calcium sensitivity of normotensive and hypertensive resistance arteries

We measured intracellular Ca2+ and isometric force simultaneously in endothelium-denuded mesenteric resistance arteries of 12- to 15-week-old male spontaneously hypertensive rats (SHR). Wistar-Kyoto (WKY) rats, and Wistar rats. Basal Ca2+ did not differ among vessels of these strains (SHR, 86.6 +/- 4.5 nmol/L; WKY, 78.5 +/- 4.7 nmol/L; Wistar, 83.1 +/- 3.9 nmol/L). Myofilament Ca2+ sensitivity was determined by measuring the intracellular Ca2+ and force responses to cumulative addition of extracellular Ca2+ (0.025 to 2.5 mmol/L) in the presence of 100 mmol/L K+ or 10 mumol/L norepinephrine after depletion of releasable intracellular Ca2+ stores. With 100 mmol/L K+, no between-strain differences in active stress, intracellular Ca2+, or myofilament Ca2+ sensitivity were observed. With 10 mumol/L norepinephrine, the active stress response of SHR vessels to 0.025 and 0.05 mmol/L Ca2+ was increased compared with both normotensive strains. The intracellular Ca2+ response was not different in vessels of SHR and WKY rats but was depressed in Wistar vessels. Myofilament Ca2+ sensitivity of SHR was elevated compared with both WKY and Wistar rats (P < .05) (ED25 for SHR, 74.4 +/- 5.1 nmol/L; WKY, 89.8 +/- 5.5 nmol/L; Wistar, 86.9 +/- 3.4 nmol/L). No strain differences in intracellular Ca2+ or active stress responses of SHR and WKY vessels were detected during cumulative addition of norepinephrine with constant extracellular Ca2+ (1.5 mmol/L). These results indicate that no hypertension-associated defect in vascular Ca2+ handling exists in mesenteric arteries of the SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

Stroke-prone SHR vascular muscle Ca2+ current amplitudes correlate with lethal increases in blood pressure

Studies on the possible causal relationship between the Ca2+ channel current density in the vascular muscle cell (VMC) and increases in blood pressure were extended by a comparison of stroke-prone spontaneously hypertensive rats (SP-SHR) with N/nih outbred normotensive rats. Maximal amplitudes of both L-type and T-type Ca2+ channel currents were significantly increased in SP-SHR without a difference in cell capacitance. SP-SHR peak current amplitudes in 20 mM Ba2+ averaged 446 +/- 64 pA while N/nih averaged 156 +/- 25 pA (clearly separated statistically). Both L-type and T-type Ba2+ currents (IBa) were significantly increased in SP-SHR, shown also by peak current frequency distributions. There was a significant shift to the left of both activation (7 mV) and inactivation (15 mV) current-voltage (I-V) plots. SP-SHR IBa recovery from inactivation was significantly slower (103 versus 61 ms) than in N/nih VMC. The increases in SP-SHR IBa amplitude under maximized conditions correlated with increases in blood pressure. Together with earlier observations of increased vascular muscle Ca2+ current density coexistent with blood pressure elevation in Kyoto-Wistar SHR, these data provide evidence for altered function of Ca2+ channels as a fundamental component of hypertension. Since the Ca2+ channel alterations exist in venous VMCs of newborn SP-SHR rats (in a low pressure blood vessel and at a time when increased Ca2+ current density could not be an effect of increased blood pressure), our results add to the growing evidence of Ca2+ channel abnormalities as a cause of genetic hypertension.

Glyburide actions on the dihydropyridine-sensitive Ca2+ channel in rat vascular muscle

The effects of glyburide, a purportedly selective ATP-sensitive K+ channel antagonist, were studied on dihydropyridine (DHP)-sensitive (L-type) Ca2+ channel currents in rat aortic muscle cells. Whole-cell voltage-clamp Ba2+ currents (IBa) were recorded at a series of test potentials (VT) from -30 to +60 mV during 300-ms voltage steps from a holding potential of -80 mV. Bay k8644 (1 microM) increased peak divalent cation currents from 47.2 +/- 15.1 to 102.6 +/- 13.4 pA, and the current-voltage relationship curve was shifted 10 mV to the left (n = 5). The combination of 10 microM glyburide with 1 microM Bay k8644 further increased Bay k8644-enhanced IBa in each cell (average of 223.7 +/- 26.4 pA, n = 5), and caused a further 10 mV hyperpolarizing (leftward) shift of the activation curve. The kinetics of IBa were also changed (more rapid inactivation) by glyburide. These stimulatory actions of glyburide were reversed on washout. In contrast to this apparent synergism with Bay k8644, 10 microM glyburide alone inhibited (rather than potentiated) IBa by about 20% at VT of 0, +10, and +30 mV. Increasing glyburide concentration to 30 microM further inhibited the IBa to about 40-50% of controls. With the pure agonist isomer, 0.5 microM Bay R5417, at theoretically the same concentration of the minus enantiomer as is present in Bay k8644, IBa increased from 137 +/- 18.3 pA to 354.2 +/- 12.4 pA (n = 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Intracellular Ca2+ and force generation determined in resistance arteries of normotensive and hypertensive rats

OBJECTIVE

Dysfunctional cellular Ca2+ handling has been proposed to underlie the heightened vascular reactivity observed in the spontaneously hypertensive rat (SHR) model of genetic hypertension. We tested the hypothesis that basal or agonist-induced mobilization of intracellular Ca2+ is elevated in mesenteric resistance arteries of SHR compared with the normotensive Wistar-Kyoto (WKY) rat.

DESIGN

A method using fura-2 for the simultaneous measurement of intracellular Ca2+ and isometric force generation in isolated mesenteric resistance arteries was employed to measure agonist-induced changes in Ca2+ and force during activation with 100 mmol/l K+ or 10 mumol/l norepinephrine. Arteries with normalized diameter 220-240 microns from male rats aged 14-15 weeks were examined.

RESULTS

No differences were detected between the rat strains in basal Ca2+ concentration or the steady-state concentration of Ca2+ achieved in response to either 100 mmol/l K+ or 10 mumol/l norepinephrine. The relationship between Ca2+ and force during the contractile responses to K+ and norepinephrine was analyzed. No differences between the strains in the level of active stress, normalized to unit intracellular Ca2+, were detected in the steady-state responses to K+ or norepinephrine.

CONCLUSIONS

The present results do not support the hypothesis that alterations in either the basal concentration of intracellular Ca2+ or the amount of intracellular Ca2+ mobilized in response to high levels of norepinephrine or K+ are present in resistance arteries of SHR compared with those of WKY rats. Moreover, these findings suggest that elevations in Ca2+ do not contribute to heightened peripheral resistance in SHR.

Neuropeptide Y increases force development through a mechanism that involves calcium entry in resistance arteries

The hypothesis that neuropeptide Y (NPY) potentiates noradrenaline (NA)-induced vascular force development by increasing free intracellular Ca2+ ([Ca2+]i) was tested in rat mesenteric resistance arteries. NPY (100 nM) alone was not able to increase either the contraction or [Ca2+]i. However, pretreatment of mesenteric resistance arteries with 100 nM NPY potentiated both [Ca2+]i and active stress induced by 1.5 microM NA. Addition of 100 nM NPY to vessels that had been precontracted with NA (1.5 microM) elicited a large increase in [Ca2+]i and an increase in active stress development. In Ca(2+)-free medium containing 2 mM ethylene glycol-bis(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid, the potentiating effect of NPY on the NA-induced contraction was prevented, and readdition of Ca2+ resulted in a large increase in both [Ca2+]i and active stress development. It is concluded that NPY potentiates NA-induced contraction in the isolated mesenteric resistance artery by inducing a rise in [Ca2+]i through an influx of Ca2 from the extracellular source.

Ca2+ channel actions of the non-dihydropyridine Ca2+ channel antagonist Ro 40-5967 in vascular muscle cells cultured from dog coronary and saphenous arteries

We studied the membrane effects of (1S,2S)-2-(2-[[3-2(benzimidazolyl) propyl]methylamino]ethyl)-6-fluoro-1, 2,3,4-tetrahydro-1-isopropyl-2-naphthyl-methoxyacetate dihydrochloride, Ro 40-5967, a new non-dihydropyridine (DHP) Ca2+ channel antagonist, on dog coronary and saphenous arterial vascular muscle cells using the whole-cell patch-clamp method. Long-lasting (L-type) inward currents in 20 mM Ba2+ were measured over a range of test potentials (300 ms) from -50 mV to +90 mV from a holding potential of -80 mV in the presence of 1 microM Bay k8644 (a DHP Ca2+ agonist). Ro 40-5967 caused a concentration-dependent suppression of Ca2+ channel currents in muscle cells from both arteries, with greater potency on coronary than saphenous arterial cells. The concentration of Ro 40-5967 which inhibited the magnitude of peak inward currents by 50% (IC50) was estimated to be 1 microM (n = 5) in muscle cells from coronary artery and 10 microM (n = 4) in saphenous artery. Ro 40-5967 (1 microM) decreased the amplitude of the activation current-voltage relationship for coronary L-type Ca2+ channel currents over a wider range of membrane potentials than verapamil, diltiazem, or nifedipine. In contrast, block of Ca2+ channel currents in saphenous artery cells by 1 microM Ro 40-5967 was only observed at command potentials positive to 0 mV. Ro 40-5967 (1 microM) significantly shifted the voltage-inactivation curve downward by 40% in coronary (n = 4), but only by 18% in saphenous arterial muscle cells (n = 3).(ABSTRACT TRUNCATED AT 250 WORDS)