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C van Breemen

Publications and source records attributed to C van Breemen.

At least 19 recordsLinked to original sources
PubMed2002

Ca(2+) removal mechanisms in freshly isolated rabbit aortic endothelial cells.

Calcium removal from the cytoplasm was investigated in freshly isolated aortic endothelial cells by monitoring changes in intracellular calcium ([Ca(2+)](i)) using ratiometric fura-2 fluorimetry. Blockade of the Na(+)/Ca(2+) exchanger (NCX) by replacement of external sodium with equi-molar N-methyl-D-glutamine (0Na PSS) decreased the removal rate by 52%. Blockade of the sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA) by cyclopiazonic acid (CPA) decreased the removal rate by 50%. Simultaneous application of CPA and 0Na PSS did not reduce the removal rate any further (53%). The lack of additivity of these two procedures, suggests that SERCA and the NCX function in series to lower [Ca(2+)](i). In addition, in the absence of extracellular Ca(2+), removal of external Na(+) markedly reduced the rate of loss of Ca(2+) from the ER further supporting the hypothesis that NCX is functionally linked to ER calcium release channels, and thus, plays an important role in ER calcium unloading. To investigate the mechanism for the coupling of NCX and SERCA, the same protocols as described above were repeated after treating the cells with cytochalasin D, which disrupts the cytoskeleton. This treatment uncoupled the NCX from SERCA, as evidenced by the resulting additive inhibitory effects of application of CPA and removal of extracellular Na(+) on the rate of Ca(2+) removal from the cytoplasm. These data suggest that in endothelial cells NCX and SERCA function in series to remove about half of the free Ca(2+) from the cytosol, while PMCA contributes to the other half of the Ca(2+) removal process.

Acetylcholine↗
PubMed2001

The mechanism of phenylephrine-mediated [Ca(2+)](i) oscillations underlying tonic contraction in the rabbit inferior vena cava.

1. We characterized the mechanisms in vascular smooth muscle cells (VSMCs) that produce asynchronous, wave-like Ca(2+) oscillations in response to phenylephrine (PE). Confocal imaging was used to observe [Ca(2+)](i) in individual VSMCs of intact inferior vena cava (IVC) from rabbits. 2. It was found that the Ca(2+) waves were initiated by Ca(2+) release from the sarcoplasmic reticulum (SR) via inositol 1,4,5-trisphosphate-sensitive SR Ca(2+) release channels (IP(3)R channels) and that refilling of the SR Ca(2+) store through the sarcoplasmic-endoplasmic reticulum Ca(2+)-ATPase (SERCA) was required for maintained generation of the repetitive Ca(2+) waves. 3. Blockade of L-type voltage-gated Ca(2+) channels (L-type VGCCs) with nifedipine reduced the frequency of PE-stimulated [Ca(2+)](i) oscillations, while additional blockade of receptor-operated channels/store-operated channels (ROCs/SOCs) with SKF96365 abolished the remaining oscillations. Parallel force measurements showed that nifedipine inhibited PE-induced tonic contraction by 27 % while SKF96365 abolished it. This indicates that stimulated Ca(2+) entry refills the SR to support the recurrent waves of SR Ca(2+) release and that both L-type VGCCs and ROCs/SOCs contribute to this process. 4. Application of the Na(+)-Ca(2+) exchanger (NCX) inhibitors 2',4'-dichlorobenzamil (forward- and reverse-mode inhibitor) and KB-R7943 (reverse-mode inhibitor) completely abolished the nifedipine-resistant component of [Ca(2+)](i) oscillations and markedly reduced PE-induced tone. 5. Thus, we conclude that each Ca(2+) wave depends on initial SR Ca(2+) release via IP(3)R channels followed by SR Ca(2+) refilling through SERCA. Na(+) entry through ROCs/SOCs facilitates Ca(2+) entry through the NCX operating in the reverse mode, which refills the SR and maintains PE-induced [Ca(2+)](i) oscillations. In addition some Ca(2+) entry through L-type VGCCs and ROCs/SOCs serves to modulate the frequency of the oscillations and the magnitude of force development.

Animals↗
PubMed2001

Mitochondrial release of apoptosis-inducing factor and cytochrome c during smooth muscle cell apoptosis.

Photodynamic therapy (PDT) is under investigation for the treatment of intimal hyperplastia in conditions such as atherosclerosis and restenosis. Although smooth muscle cells (SMCs) may be a key target for treatment, the effects of PDT on these cells are poorly characterized. In the present study, apoptosis was induced in primary human aortic SMCs by the combination of the photosensitizer verteporfin and visible light. After PDT, an increase in mitochondrial cytochrome c (cyt c) and apoptosis-inducing factor (AIF) levels were detected in the cytosol immediately and their levels increased steadily up to 2 hours. Cytosolic levels of the pro-apoptotic Bcl-2 family member Bax decreased reciprocally throughout this period, but this change did not occur before cyt c release. Confocal microscopy revealed a diffuse staining pattern of cyt c within apoptotic cells as compared to a distinct mitochondrial staining in normal cells. AIF translocated from mitochondria to the nucleus during the progression of apoptosis. After cyt c release, caspase-9 and caspase-3 processing was visible by 1 hour and caspase-6, -7, and -8 processing was apparent by 2 hours after PDT. In summary, these results demonstrate for the first time the cellular redistribution of mitochondrial AIF during SMC apoptosis, as well as the early release of cyt c and the subsequent activation of multiple caspases during PDT-induced SMC apoptosis.

Aorta↗
PubMed2001

Hepatic over-expression of peroxisome proliferator activated receptor gamma2 in the ob/ob mouse model of non-insulin dependent diabetes mellitus.

Studies of the molecular basis of insulin resistance have focused on the peroxisome proliferator activated receptor gamma (PPARgamma, gamma1 and gamma2). The aim of this study was to determine whether the insulin resistance in liver of diabetic animals is associated with abnormal expression of these receptors. PPARgamma mRNA and protein expression levels were quantified in liver of 9-week-old male ob/ob mice as a model of diabetes and compared to age- and gender-matched wild type control animals of the same genetic background. Semi-quantitative reverse transcription-polymerase chain reaction, using 18S rRNA as an internal standard, indicated that PPARgamma2 mRNA was significantly upregulated in ob/ob liver vs. that in wild type mice. Western blotting revealed greater immunoreactivity of PPARgamma2 in liver from ob/ob mice relative to that in wild type mice. An index of insulin resistance (product of serum glucose and insulin concentration) was correlated with liver PPARgamma2 mRNA expression (r = 0.776; p < 0.001). The findings that liver PPARgamma2 expression is (1) significantly elevated in the ob/ob model of diabetes and (2) positively associated with an index of insulin resistance, suggests a possible compensatory response through which type II diabetic and obese organisms strive to maintain insulin sensitivity of the liver.

Adipose Tissue↗
PubMed2001

Bcl-2 increases emptying of endoplasmic reticulum Ca2+ stores during photodynamic therapy-induced apoptosis.

Photodynamic therapy (PDT) is clinically approved for the treatment of several types of cancer as well as age-related macular degeneration, the leading cause of blindness in the elderly. PDT using the photosensitizer verteporfin has been previously shown to induce rapid apoptosis via a mitochondrial-caspase activation pathway. The impact of PDT on other cellular organelles such as the endoplasmic reticulum (ER) is undefined. The effect of PDT on intracellular Ca2+ ([Ca2+]i) in control and Bcl-2-overexpressing HeLa cells was assessed. A greater [Ca2+]i transient was observed for Bcl-2 overexpressing cells in response to PDT. The PDT-induced Ca2+ release was due to the emptying of Ca2+ from ER and possibly mitochondrial stores and was not due to an influx of Ca2+ from the medium. For Bcl-2-transfected cells, the release of Ca2+ was incomplete as determined by a further [Ca2+]i transient produced by the addition of the Ca2+ ionophore ionomycin after PDT. Furthermore, extrusion of Ca2+ was not hindered while ER-mediated sequestration of Ca2+ was impaired after PDT. Impairment of ER-mediated sequestration of Ca2+ may be due to the immediate caspase-independent depletion of sarco/endoplasmic reticulum Ca2+ ATPase-2 (SERCA2) that occurred in response to PDT in birth HeLa/Neo and Bcl-2 overexpressed HeLa cells. In summary, PDT induced the rapid degradation of SERCA2 and release of ER and mitochondrial Ca2+ stores. Although overexpression of Bcl-2 did not protect against SERCA2 degradation, it may influence the release of Ca2+ from ER and mitochondrial stores in PDT-treated cells.

Apoptosis↗
PubMed2001

Role of Ca2+-sensitive protein kinase C in phenylephrine enhancement of Ca2+ sensitivity in rat tail artery.

We investigated the role of protein kinase C (PKC) isoforms on changes in sensitivity of contractile mechanisms to intracellular Ca(2+) (force /[Ca(2+)]i) by phenylephrine (0.1-100 microM) in rat tail arterial helical strips using simultaneous measurements of force and [Ca(2+)]i. Force/[Ca(2+)]Ii induced by phenylephrine was greater than that induced by 80 mM K+. Force/[Ca(2+)]i induced by phenylephrine in physiologic saline solution or low Ca(2+) solution was dependent on the agonist concentration. Removal of Ca(2+) completely abolished the phenylephrine-induced contraction. The PKC inhibitors staurosporine and calphostin C inhibited the increase in force/[Ca(2+)]i induced by phenylephrine to a much greater extent than that induced by 80 mM K+. LY379196, a specific PKCbeta inhibitor, did not inhibit the increase of calcium sensitivity due to phenylephrine. The classic PKC isoforms, alpha, betaI, and II not gamma were demonstrated in the artery by immunohistochemistry. These results suggest that in rat tail arterial smooth muscle, PKCalpha, and not beta or gamma, mediates the increase of changes in sensitivity of contractile mechanisms to intracellular Ca(2+) to high dose of alpha1 receptor stimulation (phenylephrine 100 microM) on nonphysiologic conditions.

Animals↗
PubMed2001

Role of sarcoplasmic reticulum in regulation of tonic contraction of rabbit basilar artery.

Superficial sarcoplasmic reticulum (SR) regulates smooth muscle force development directly by Ca(2+) release and removal to and from the cytoplasm (Somlyo and Somlyo. J Cardiovasc Pharmacol 8, Suppl 8: S42-S47, 1986) by buffering Ca(2+) influx and contributing to Ca(2+) extrusion (Mueller and van Breemen. Nature 281: 682-683, 1979) and indirectly by releasing Ca(2+) near Ca(2+)-activated K(+) channels (K(Ca)) to hyperpolarize the plasma membrane (Bolton and Imaizumi. Cell Calcium 20: 141-152, 1996 and Nelson et al. Science 270: 633-637, 1995). In the rabbit basilar artery, relative contributions of direct effects and those mediated through activation of K(Ca) were evaluated by measuring force and intracellular Ca(2+) concentration ([Ca(2+)](i)) in response to the SR-depleting agents thapsigargin and ryanodine and the large conductance K(Ca) (BK(Ca)) blockers iberiotoxin (IbTX) and tetraethylammonium ion (TEA). A large contraction was observed in response to K(Ca) blockade with either 3 mM TEA or 100 nM IbTX and also after addition of 10 microM ryanodine or 2 microM thapsigargin. When K(Ca) was blocked first with TEA or IbTX, subsequent addition of thapsigargin or ryanodine also increased force. Measurements of fura 2 fluorescence showed parallel increases in [Ca(2+)](i) in response to sequential blockade of sarco(endo)plasmic reticulum Ca(2+)-ATPase and K(Ca) regardless of the order of application. It appears that a significant fraction of K(Ca) remains activated in the absence of SR function and that SR contributes to relaxation after blockade of K(Ca). We found that depletion of SR before stimulating Ca(2+) influx through voltage-gated Ca(2+) channels markedly reduced force development rate and that thapsigargin abolished this effect. We conclude that the SR of rabbit cerebral arteries modulates constriction by direct and indirect mechanisms.

Animals↗
PubMed2000

Profound inhibition of myogenic tone in rat cardiac allografts is due to eNOS- and iNOS-based nitric oxide and an intrinsic defect in vascular smooth muscle contraction.

BACKGROUND: The physiological consequences of inducible NO synthase (iNOS) expression were studied in allograft coronary arteries by pressure myography. METHODS AND RESULTS: Septal coronary arteries (diameter, 200.6+/-3.3 microm) were harvested from allograft and isograft hearts, and their myogenic properties were measured before and after iNOS and nonselective NOS inhibition with aminoguanidine (AG, 100 micromol/L) and N(G)-nitro-L-arginine methyl ester (L-NAME) (200 micromol/L). Fura 2 fluorescence microscopy was used to measure [Ca(2+)](i) in isolated endothelial cells. Monoclonal anti-iNOS immunostains demonstrated iNOS protein in day 2, 7, 14, and 28 allograft vessels, but only in day 2 isograft vessels. Myogenic tone was profoundly inhibited in allograft vessels from day 4 onward. In day 4 allograft vessels, these differences were abolished by L-NAME but not AG, suggesting greater basal release of eNOS-based NO from allograft endothelium. Fluorescence measurements confirmed elevation of [Ca(2+)](i) in day 4 allograft endothelium, providing a mechanism for enhanced eNOS activity. For days 7 to 28, AG potentiated myogenic tone in allograft but not isograft vessels, indicating that vasoactive iNOS-based NO was present. In mature vessels, constriction via agonist- and depolarization-mediated mechanisms showed parallel inhibition, suggesting an intrinsic defect in vascular smooth muscle cell contraction. CONCLUSIONS: Our data indicate that the profound inhibition of myogenic tone in allograft arteries involves direct vasodilation by eNOS- and iNOS-based NO, as well as an intrinsic defect in vascular smooth muscle contraction. The hemodynamic profile resulting from these changes in allograft resistance vessel function would favor movement of extracellular fluid from the intravascular space into the myocardial interstitium, resulting in edema, increased ventricular stiffness, and poor ventricular performance.

Animals↗
PubMed2000

Asynchronous Ca(2+) waves in intact venous smooth muscle.

The rabbit inferior vena cava (IVC) is a large-capacitance vessel that displays typical contractile dose-response curves for caffeine and phenylephrine (PE). Using confocal microscopy on the endothelium-denuded IVC, we undertook experiments to correlate these whole-tissue contractile dose-response curves with changes in subcellular [Ca(2+)](i) signals in the in situ vascular smooth muscle cells (VSMCs). We observed that both caffeine and PE initially elicited Ca(2+) waves in individual VSMCs. The [Ca(2+)](i) in cells challenged with caffeine subsequently returned to baseline whereas the [Ca(2+)](i) in cells challenged with PE exhibited repetitive asynchronous Ca(2+) waves. These [Ca(2+)](i) oscillations were related to Ca(2+) release from the sarcoplasmic reticulum as they were inhibited by ryanodine and caffeine. The lack of synchronicity of the [Ca(2+)](i) oscillations between VSMCs can explain the observed tonic contraction at the whole-tissue level. The nature of these Ca(2+) waves was further characterized. For caffeine, the amplitude was all-or-none in nature, with individual cells differing in sensitivity, leading to their recruitment at different concentrations of the agonist. This concentration dependency of recruitment appears to form the basis for the concentration dependency of caffeine-induced contraction. Furthermore, the speed of the Ca(2+) waves correlated positively with the concentration of caffeine. In the case of PE, we observed the same characteristics with respect to wave speed, amplitude, and recruitment. Increasing concentrations of PE also enhance the frequency of the [Ca(2+)](i) oscillations. We therefore conclude that PE stimulates whole-tissue contractility through differential recruitment of VSMCs and enhancement of the frequency of asynchronous [Ca(2+)](i) oscillations once the cells are recruited.

Animals↗
PubMed2000

Activation of purinergic P2X receptors inhibits P2Y-mediated Ca2+ influx in human microglia.

Purinoceptor (P2X and P2Y) mediated Ca2+ signaling in cultured human microglia was studied using Ca2+ sensitive fluorescence microscopy. ATP (at 100 microM) induced a transient increase in [Ca2+]i in both normal and Ca(2+)-free solution suggesting a primary contribution by release from intracellular stores. This conclusion was further supported by the failure of ATP to cause a divalent cationic influx in Mn2+ quenching experiments. However, when fluorescence quenching was repeated after removal of extracellular Na+, ATP induced a large influx of Mn2+, indicating that inward Na+ current through a non-selective P2X-coupled channel may normally suppress divalent cation influx. Inhibition of Mn2+ entry was also found when microglia were depolarized using elevated external K+ in Na(+)-free solutions. The possibility of P2X inhibition of Ca2+ influx was then investigated by minimizing P2X contributions of purinergic responses using either the specific P2Y agonist, ADP-beta-S in the absence of ATP or using ATP combined with PPADS, a specific inhibitor of P2X receptors. In quenching studies both procedures resulted in large increases in Mn2+ influx in contrast to the lack of effect observed with ATP. In addition, perfusion of either ATP plus PPADS or ADP-beta-S alone caused a significantly enhanced duration (about 200%) of the [Ca2+]i response relative to that induced by ATP. These results show that depolarization induced by P2X-mediated Na+ influx inhibits store-operated Ca2+ entry resulting from P2Y activation, thereby modulating purinergic signaling in human microglia.

Adenosine Diphosphate↗
PubMed1999

Nonspecific inhibition of myogenic tone by PD98059, a MEK1 inhibitor, in rat middle cerebral arteries.

Activation of MAP kinase kinase, also called ERK kinase (MEK), may lead to desinhibition of thin filament regulatory proteins and we therefore investigated the acute effects of the potent MEK inhibitor, PD98059 on the contractile properties of pressurized rat middle cerebral arteries. Cerebral arteries (diameter 100-150 microm) were mounted on a pressure myograph and PD98059 (10 microM, 40 microM) significantly inhibited (15% and 64%) myogenic tone (P < 0.001). At these concentrations, PD98059 also significantly reduced the vasopressin (0.1 microM)- and KCl (60 mM)-induced tone. Cumulative addition of exogenous Ca2+ (0.4-1.6 mM) increased myogenic tone to approximately 50% of constriction at 80 mmHg. This effect was inhibited by PD98059 (P < 0.001). These results demonstrate that pressure-induced myogenic tone is inhibited by PD98059 at the concentrations that have been reported to be selective for inhibition of MEK and the MAP kinase cascade. However, our results also demonstrate that PD98059 may have nonspecific effects on voltage-sensitive Ca2+ entry in vascular smooth muscle.

Animals↗
PubMed1999

Depolarization-mediated inhibition of Ca(2+) entry in endothelial cells.

The effect of extracellular Cl(-) in regulating ACh-induced Ca(2+) entry into freshly isolated rabbit aortic endothelial cells was studied using Ca(2+)-sensitive fluorescence microscopy and patch-clamp electrophysiology. After ACh caused transient Ca(2+) release in Ca(2+)-free medium, readdition of 3 mM Ca(2+) to the bath maintained Ca(2+) entry. Removal of extracellular Cl(-) abolished the plateau phase in Ca(2+) signal and inhibited divalent cation entry. However, in the presence of the K(+) ionophore valinomycin, removal of Cl(-) had no effect on the Ca(2+) plateau. Under current-clamp conditions, substitution of gluconate for Cl(-) induced membrane depolarization. Under voltage clamp, with CsCl in the pipette, ACh activated a slowly developing Cl(-) current, which was blocked by SITS and 5-nitro-2-(3-phenylpropylamino)benzoic acid. Varying the membrane potential by utilizing different extracellular K(+) concentrations in the presence of 5 microM valinomycin demonstrated that depolarization blocked ACh-stimulated Mn(2+) entry. These data suggest that ACh-induced Ca(2+) entry in freshly isolated endothelial cells requires the presence of extracellular Cl(-) to maintain a polarized membrane potential.

Acetylcholine↗
PubMed1999

Heterogeneity of endothelium-dependent vasodilation in pressurized cerebral and small mesenteric resistance arteries of the rat.

We compared endothelial responses to calcium-mobilizing agents in mesenteric and cerebral resistance arteries of the rat. Middle cerebral and small mesenteric arteries were mounted in a pressure myograph, and myogenic responses were recorded. The effects of acetylcholine (ACh), bradykinin, substance P, histamine, A23187, cyclopiazonic acid (CPA), and sodium nitroprusside were investigated in both arteries with myogenic tone in the absence and presence of nitric oxide synthase and cyclooxygenase inhibitors. The effects of raised potassium, K(+) channel blockers, and arachidonic metabolism inhibition were examined on the nitric oxide (NO) synthase/cyclooxygenase inhibitor-resistant dilation induced by ACh and CPA. Cerebral arteries display a high level of myogenic reactivity compared with mesenteric arteries. In cerebral arteries, only bradykinin and substance P induced endothelium-dependent dilation. The observed dilation was solely related to the activation of the NO pathway. However, in mesenteric arteries, all of the vasoactive agents induced endothelium-dependent dilation. A combination of NO, cyclooxygenase-derived prostanoids, and a factor with endothelium-derived hyperpolarizing factor-like properties was responsible for the observed vasodilation. NO and cyclooxygenase derivatives were able to compensate for each other in the CPA-induced endothelium-dependent vasodilation when one of the two pathways was blocked. Moreover, small Ca(2+)-activated K(+) channels and a combination of both large and small Ca(2+)-activated K(+) channels were implicated in the endothelium-derived hyperpolarizing factor-like component of dilation to ACh and CPA, respectively. Finally, the results suggest that the pathway by which agonists raise intracellular calcium concentration may determine the nature of the endothelial secretory product.

Animals↗
PubMed1998

Gender difference in the basal intracellular Ca2+ concentration in rat valvular endothelial cells.

Intracellular Ca2+ concentration ([Ca2+]i) was measured by Fura 2/AM fluorescence imaging microscopy in freshly isolated valvular endothelial cells taken from female and male rats. The basal level of [Ca2+]i was significantly elevated in female valvular endothelial cells when compared to males (P < 0.05). Inhibition of the sarco-endoplasmic reticulum Ca(2+)-ATPase with cyclopiazonic acid (CPA, 10 microM) caused a greater increase in the [Ca2+]i in female than male endothelial cells. Removal of extracellular Ca2+ returned the [Ca2+]i to the basal level. The rate of [Ca2+]i decline was significantly slower in female endothelial cells compared to males. There were no differences in the unstimulated rate of Mn2+ quenching between two groups. These results demonstrate that estrogen affects NOS at least in part, by an alteration in Ca2+ homeostasis in endothelial cells.

Animals↗
PubMed1998

Functional linkage of Na(+)-Ca2+ exchange and sarcoplasmic reticulum Ca2+ release mediates Ca2+ cycling in vascular smooth muscle.

Ca2+ loss from the sarcoplasmic reticulum (SR) of rabbit inferior vena cava smooth muscle was monitored by measuring the decay of caffeine-induced fura-2 fluorescence transients. Removal of Ca2+ from the extracellular space caused a rapid loss of SR Ca2+ and a decline of cytoplasmic Ca2+ concentration ([Ca2+]i). Simultaneous removal of extracellular Na+ greatly inhibited the rate of this (SR) Ca2+ loss. A rapid loss of SR Ca2+ was induced by 20 microns CPA, regardless of the presence or absence of extracellular Na+ or Ca2+. These effects were not influenced by alterations in membrane potential owing to activity of Ca2(+)-activated K+ channels since 3 mM TEA had no effect on the rate of Ca2+ loss from the SR. These results indicate that when Ca2+ is removed from the extracellular space, it induces Ca2+ release from the SR towards the plasma membrane Na(+)-Ca2+ exchanger which subsequently translocates it from the junctional cytoplasmic space to the extracellular space. When the Na(+)-Ca2+ exchanger is arrested by removal of extracellular Na+ and Ca2+, Ca2+ released from the SR is re-sequestered by the sarco-endo-plasmic reticulum Ca2(+)-ATPase (SERCA). However, when both the Na(+)-Ca2+ exchanger, and, the SERCA are blocked, Ca2+ released from the SR is extruded from the cells by the plasma membrane Ca2(+)-ATPase. These results reveal a hierarchy of interaction between the different Ca2+ transporters in the SR, and cell membranes.

Animals↗
PubMed1998

Endothelium-smooth muscle interaction in cardiac transplantation.

1. The inducible isoform of nitric oxide synthase (iNOS) is expressed in human and experimental cardiac allografts and is localized to infiltrating macrophages, cardiac myocytes, endothelial cells and smooth muscle cells. A recent clinical report proposes a causal link between myocardial expression of iNOS and ventricular contractile dysfunction, a potentially graft- and life-threatening post-transplant complication. 2. Coronary blood flow is elevated in human graft recipients with biopsy proven cellular rejection, indicating that vasodilation accompanies graft rejection. In Lewis-to-F-344 coronary resistance vessels, which show intimal expression of iNOS, pressure-induced myogenic tone is significantly inhibited. Selective iNOS inhibition partially reverses the inhibition of myogenic tone, confirming that iNOS produces vasoactive nitric oxide (NO) and may mediate the rejection-induced vasodilation seen clinically. 3. Endothelial dysfunction, identified as loss of endothelium-dependent dilation, has tremendous prognostic significance in vascular diseases of multiple aetiologies. In transplantation, endothelial dysfunction predicts early cardiac allograft vasculopathy and poor clinical outcome. Lewis-to-F-344 coronary vessels develop endothelial dysfunction at 1 week post-transplantation, but this is preceded by a transient state of endothelial cell hyperfunction, with enhanced endothelial production of NO. 4. The normal interaction between endothelial and smooth muscle cells in coronary resistance vessels is critical for the regulation of coronary blood flow and the maintenance of fluid homeostasis. With allospecific expression of iNOS, the inhibition of vascular tone predicts greatly enhanced intravascular pressure in precapillary arterioles and capillaries; this would be expected to cause a net movement of fluid from the intravascular compartment into the myocardial interstitium, resulting in ventricular oedema, non-compliance and poor contractile performance.

Cell Survival↗