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Biomedical subjects

J Marc Simard

Publications and source records attributed to J Marc Simard.

At least 19 recordsLinked to original sources
PubMed2006

EGF and HB-EGF modulate inward potassium current in human bladder urothelial cells from normal and interstitial cystitis patients.

Interstitial cystitis (IC) is an idiopathic condition characterized by bladder hyperalgesia. Studies have shown cytokine and purinergic signaling abnormalities in cultured bladder urothelial cells (BUC) from IC patients. We performed single-cell electrophysiological studies in both normal and IC BUC. A strongly inward rectifying potassium current with conductance of the Kir2.1 channel was identified in normal BUC. This current was significantly reduced in IC BUC. Kir2.1 protein and mRNA were detected in both IC and normal BUC. Epidermal growth factor (EGF) caused a dose-dependent decrease in the inward potassium current in normal BUC. EGF is secreted in higher amounts by IC BUC and is known to decrease Kir2.1 conductance by phosphorylation of Kir2.1. Genistein, a nonspecific phosphorylation inhibitor, increased the inward potassium current in IC BUC and blocked the effect of EGF on normal BUC. Treatment of IC BUC with heparin-binding epidermal growth factor-like growth factor (HB-EGF), previously shown to be secreted in lower amounts by IC BUC, significantly increased inward potassium current. These data show that the inward potassium current in BUC can be modulated by EGF and HB-EGF. Changes in BUC membrane potassium conductance caused by altered levels of EGF and HB-EGF may therefore play a role in the pathophysiology of IC.

Cells, Cultured↗
PubMed2006

Recommendations of the National Heart, Lung, and Blood Institute working group on cerebrovascular biology and disease.

The National Heart, Lung, and Blood Institute (NHLBI) convened a conference call working group, consisting of experts in stroke and cerebrovascular biology on January 28, 2005. The purpose of this working group was to develop a prioritized set of recommendations for NHLBI to establish a focused and comprehensive set of research activities in cerebrovascular biology and disease. Three thematic areas of research emerged: (1) molecular and cellular neurobiology of cerebral blood vessels, focusing on genomics and proteomics, neurovascular signaling and cerebrovascular embryogenesis, development and plasticity; (2) resource development, involving the development of new methodological approaches for normal and altered function of the neurovascular unit, collaborative research, and training in cerebrovascular pathobiology; and (3) cerebrovascular diseases and translational approaches, addressing vascular mechanisms of disease, the role of risk factors, importance of biomarkers with the ultimate goal of developing new treatments.

Animals↗
PubMed2006

Newly expressed SUR1-regulated NC(Ca-ATP) channel mediates cerebral edema after ischemic stroke.

Pathological conditions in the central nervous system, including stroke and trauma, are often exacerbated by cerebral edema. We recently identified a nonselective cation channel, the NC(Ca-ATP) channel, in ischemic astrocytes that is regulated by sulfonylurea receptor 1 (SUR1), is opened by depletion of ATP and, when opened, causes cytotoxic edema. Here, we evaluated involvement of this channel in rodent models of stroke. SUR1 protein and mRNA were newly expressed in ischemic neurons, astrocytes and capillaries. Upregulation of SUR1 was linked to activation of the transcription factor Sp1 and was associated with expression of functional NC(Ca-ATP) but not K(ATP) channels. Block of SUR1 with low-dose glibenclamide reduced cerebral edema, infarct volume and mortality by 50%, with the reduction in infarct volume being associated with cortical sparing. Our findings indicate that the NC(Ca-ATP) channel is crucially involved in development of cerebral edema, and that targeting SUR1 may provide a new therapeutic approach to stroke.

ATP-Binding Cassette Transporters↗
PubMed2005

Adenylate cyclase 5 and KCa1.1 channel are required for EGFR up-regulation of PCNA in native contractile rat basilar artery smooth muscle.

In synthetic phenotype vascular smooth muscle cells (VSMC), activation of epidermal growth factor (EGF) receptor (EGFR) induces a sustained increase in intermediate conductance K(Ca) (int-K(Ca); K(Ca)3.1) channels that is essential for proliferation. However, a comparable mechanism has not been identified in native contractile phenotype VSMC, which express large conductance K(Ca) (maxi-K(Ca); K(Ca)1.1) channels, not int-K(Ca) channels. Using patch clamp of freshly isolated contractile VSMC from rat basilar artery, we found that EGF (100 ng ml(-1)) caused hyperpolarization (7.9 +/- 3.9 mV) due to activation of iberiotoxin-sensitive, maxi-K(Ca) channels. The EGFR ligands EGF (100 ng ml(-1)), transforming growth factor alpha (0.4 ng ml(-1)) and heparin-binding EGF (100 ng ml(-1)) all caused a 20% increase in maxi-K(Ca) channel current that was blocked by AG-1478 or by knock-down of EGFR expression using cisterna magna infusion of antisense oligodeoxynucleotide (AS-ODN). In controls, EGFR knock-down, and EGFR gain-of-expression (angiotensin II hypertension), the increase in maxi-K(Ca) current correlated with the abundance of EGFR protein expressed. The EGFR-mediated increase in maxi-K(Ca) channel activity was blocked by inhibiting cAMP-dependent protein kinase (cAK) using KT-5720 or Rp-cAMP, or by inhibiting adenylate cyclase type 5 (AC-5) using 2',5'-dideoxyadenosine or knock-down of AC-5 expression by intracisternal AS-ODN. Direct infusion of EGF into cisterna magna caused up-regulation of proliferating cell nuclear antigen (PCNA) in VSMC that was prevented by coinfusion of iberiotoxin or of AG-1478. Our data, which are consistent with the hypothesis that hyperpolarization is critical for a proliferative response, are the first to implicate AC-5 and maxi-K(Ca) channels in gene activation related to EGFR signalling in native contractile VSMC.

Adenylyl Cyclase Inhibitors↗
PubMed2005

Concomitant GRID boost for Gamma Knife radiosurgery.

We developed an integrated GRID boost technique for Gamma Knife radiosurgery. The technique generates an array of high dose spots within the target volume via a grid of 4-mm shots. These high dose areas were placed over a conventional Gamma Knife plan where a peripheral dose covers the full target volume. The beam weights of the 4-mm shots were optimized iteratively to maximize the integral dose inside the target volume. To investigate the target volume coverage and the dose to the adjacent normal brain tissue for the technique, we compared the GRID boosted treatment plans with conventional Gamma Knife treatment plans using physical and biological indices such as dose-volume histogram (DVH), DVH-derived indices, equivalent uniform dose (EUD), tumor control probabilities (TCP), and normal tissue complication probabilities (NTCP). We found significant increase in the target volume indices such as mean dose (5%-34%; average 14%), TCP (4%-45%; average 21%), and EUD (2%-22%; average 11%) for the GRID boost technique. No significant change in the peripheral dose coverage for the target volume was found per RTOG protocol. In addition, the EUD and the NTCP for the normal brain adjacent to the target (i.e., the near region) were decreased for the GRID boost technique. In conclusion, we demonstrated a new technique for Gamma Knife radiosurgery that can escalate the dose to the target while sparing the adjacent normal brain tissue.

Algorithms↗
PubMed2004

Regulation by sulfanylurea receptor type 1 of a non-selective cation channel involved in cytotoxic edema of reactive astrocytes.

Hypoxia-ischemia and ATP depletion are associated with cytotoxic edema of glial cells, but mechanisms involved remain incompletely characterized. We examined morphologic and electrophysiological responses of freshly isolated native reactive astrocytes (NRAs) following exposure to NaN3, which depletes cellular ATP. NaN3 caused profound and sustained depolarization due to activation of a novel 35 pS Ca2+-activated, [ATP]i-sensitive non-selective cation (NCCa-ATP) channel found in >90% of excised membrane patches. This channel exhibited significantly different properties compared with previously reported NCCa-ATP channels, including different sensitivity to block by various adenine nucleotides (EC50=0.79 microM for [ATP]i, with no block by AMP or ADP), and activation by submicromolar [Ca]i. In addition, the channel was found to be regulated in a manner identical to that of SUR1-regulated KATP channels, including high affinity block by glybenclamide and tolbutamide, and opening by diazoxide. mRNA transcription and protein expression of SUR1 but not SUR2 were confirmed in reactive astrocytes both in situ and after isolation, whereas Kir6.x, which forms the pore-forming subunit of the KATP channel, was not expressed. Channel opening by [ATP]i depletion or exposure to diazoxide caused blebbing of the cell membrane, whereas [ATP]i depletion in the presence of glybenclamide did not. These findings are consistent with participation of this channel in cation flux involved in cell swelling. This novel channel may play an important role in the pathogenesis of brain swelling.

ATP-Binding Cassette Transporters↗
PubMed2003

Alternative splicing of cGMP-dependent protein kinase I in angiotensin-hypertension: novel mechanism for nitrate tolerance in vascular smooth muscle.

Nitrate tolerance (NT) in hypertension is attributed to reduced activity of soluble guanylyl cyclase (sGC). We examined NT in basilar artery vascular smooth muscle cells (VSMCs) from control rats, rats infused with angiotensin II (Ang; 240 microg/kg per hour for 4 days), which were normotensive, and Ang-hypertensive rats (AHR; 240 microg/kg per hour for 28 days). Ca2+-activated K+ (Maxi-K) channels in VSMCs from AHR showed reduced activation by NO donor, consistent with NT. The concentration-response relationship for 8-Br-cGMP was shifted 2.5-fold to the right, indicating that abnormal sGC alone could not account for NT. Inside-out patches from AHR showed normal activation with exogenous cGMP-dependent protein kinase I (cGKI), suggesting no abnormality downstream of cGKI. We hypothesized that the reduction in apparent affinity of 8-Br-cGMP for cGKI in AHR might be due to a change in relative amounts of cGKIalpha versus cGKIbeta, since cGKIbeta is less sensitive to cGMP activators than cGKIalpha. This was substantiated by showing the following in AHR: (1) reduced effect of the cGKIalpha-selective activator 8-APT-cGMP; (2) reduced total cGKI protein (both isoforms), but an increase in cGKIbeta protein in quantitative immunofluorescence and Western blots; (3) similar changes in cGKI isoforms immunoisolated with Maxi-K channels; and (4) a large increase in cGKIbeta mRNA and a decrease in cGKIalpha mRNA in real-time PCR and Northern blots. Upregulation of cytosolic cGKIbeta was evident 4 days after Ang infusion, before development of hypertension. Our data identify a functional role for cGKIbeta in VSMCs previously ascribed exclusively to cGKIalpha. Ang-induced alternative splicing of cGKI represents a novel mechanism for reducing sensitivity to NO/cGMP.

Alternative Splicing↗
PubMed2003

Functional coupling between sulfonylurea receptor type 1 and a nonselective cation channel in reactive astrocytes from adult rat brain.

We previously identified a novel, nonselective cation channel in native reactive (type R1) astrocytes (NR1As) from injured rat brain that is regulated by cytoplasmic Ca2+ and ATP (NC(Ca-ATP)) and exhibits sensitivity to block by adenine nucleotides similar to that of sulfonylurea receptor type 1 (SUR1). Here we show that SUR1 is involved in regulation of this channel. NR1As within the site of injury and after isolation exhibited specific binding of FITC-tagged glibenclamide and were immunolabeled with anti-SUR1 antibody, but not with anti-SUR2, anti-Kir6.1 or anti-Kir6.2 antibodies, indicating absence of ATP-sensitive K+ (KATP) channels. RT-PCR confirmed transcription of mRNA for SUR1 but not SUR2. Several properties previously associated exclusively with SUR1-regulated KATP channels were observed in patch-clamp experiments using Cs+ as the charge carrier: (1) the sulfonylureas, glibenclamide and tolbutamide, inhibited NCCa-ATP channels with EC50 values of 48 nm and 16.1 microm, respectively; (2) inhibition by sulfonylureas was lost after exposure of the intracellular face to trypsin or anti-SUR1 antibody; (3) channel inhibition was caused by a change in kinetics of channel closing, with no change in channel amplitude or open-channel dwell times; and (4) the SUR activator ("KATP channel opener"), diazoxide, activated the NCCa-ATP channel, whereas pinacidil and cromakalin did not. Also, glibenclamide prevented cell blebbing after ATP depletion, whereas blebbing was produced by exposure to diazoxide. Our data indicate that SUR1 is functionally coupled to the pore-forming portion of the NC(Ca-ATP) channel, providing the first demonstration of promiscuity of SUR1 outside of the K+ inward rectifier family of channels.

ATP-Binding Cassette Transporters↗
PubMed2003

Trans-cellular proliferating cell nuclear antigen gene activation in cerebral vascular smooth muscle by endothelial oxidative injury in vivo.

OBJECTIVE: This study was undertaken to assess the role of vascular smooth muscle cell (VSMC) Ca2+ channels and Ca2+/calmodulin-dependent protein kinase II (CaMKII) in gene regulation after oxidative endothelial injury (OEI). METHODS AND RESULTS: OEI was produced by infusion of Na fluorescein (NaFluo) photoactivated by UV light immediately before intravenous injection. Posterior cerebral arteries were studied using immunofluorescence imaging, Western blotting, or patch clamping of isolated cells. After infusion of photoactivated NaFluo, but not NaFluo, (1) superoxide dismutase-1 (SOD-1) was upregulated in endothelium, consistent with oxidant stress; (2) the fraction of VSMC nuclei labeled for proliferating cell nuclear antigen (PCNA) increased 7-fold at 6 hours, preceded by a several-fold increase in nuclear phospho-cAMP-response element binding protein, with PCNA upregulation prevented by pretreatment with polyethylene glycol (PEG)-SOD; (3) in VSMCs, phospho-CaMKII increased 20-fold 5 minutes after OEI, with a 2-fold increase in peak Ca2+ channel currents; and (4) changes in cAMP-response element binding protein and PCNA were blocked by systemic administration of lipophilic (nifedipine) or hydrophilic (amlodipine) 1,4-dihydropyridine Ca2+ channel blockers, the calmodulin inhibitor trifluoperazine, or the CaMKII inhibitor KN-93, with none of these agents preventing SOD-1 upregulation in endothelium. CONCLUSIONS: Activation of VSMC Ca2+ channels and CaMKII is a key early signaling event required for upregulation of PCNA gene expression in VSMCs after oxidative injury to endothelium.

Animals↗
PubMed2003

Mislocalization of eNOS and upregulation of cerebral vascular Ca2+ channel activity in angiotensin-hypertension.

We tested the hypothesis that endothelial dysfunction induced by angiotensin II (Ang-hypertension) would impair regulatory control of vascular smooth muscle L-type Ca2+ channels by endothelial nitric oxide synthase (eNOS). We studied cerebral lenticulostriate arterioles (LSAs) from control rats, from rats infused with Ang (240 microg x kg(-1) x h(-1) SQ x4 days), which were normotensive, and from Ang-hypertensive rats (AHR; 240 microg x kg(-1) x h(-1) x28 days). Patch-clamp measurements on isolated LSA smooth muscle cells (SMCs) showed a significant increase in Ca2+ channel availability with 4- and 28-day infusions versus controls (0.47+/-0.03 and 0.66+/-0.05 vs 0.36+/-0.03 pS/pF, respectively; P<0.01), with Western blots showing no change in channel protein expression, consistent with altered channel regulation. In LSAs from 28-day AHR, 4,5-diaminofluorescein diacetate imaging showed diminished NO production in response to acetylcholine stimulation in vivo, and inhibition of eNOS with NG-nitro-L-arginine methyl ester failed to increase Ca2+ channel availability in isolated SMCs, indicating an abnormality with the eNOS/NO-signaling pathway regulating the channel. Immunofluorescence imaging showed that in 1 of 53, 33 of 109, and 53 of 62 LSAs from controls and from rats with 4- and 28-day infusions, respectively, eNOS was absent from its normal location at the abluminal border and was mislocalized to perinuclear Golgi. Ca2+ channel availability in LSA SMCs from controls and from rats with 4- and 28-day infusions was proportional to the fraction of LSAs showing eNOS mislocalization, but not blood pressure. These data provide the first evidence linking Ang-induced eNOS mislocalization, eNOS dysfunction, and Ca2+ channel upregulation, and they provide novel mechanistic insights into pathological changes in LSAs associated with stroke.

Angiotensin II↗
PubMed2003

Chlorotoxin-sensitive Ca2+-activated Cl- channel in type R2 reactive astrocytes from adult rat brain.

Astrocytes express four types of Cl(-) or anion channels, but Ca(2+)-activated Cl(-) (Cl(Ca)) channels have not been described. We studied Cl(-) channels in a morphologically distinct subpopulation ( approximately 5% of cells) of small (10-12 micro m, 11.8 +/- 0.6 pF), phase-dark, GFAP-positive native reactive astrocytes (NRAs) freshly isolated from injured adult rat brains. Their resting potential, -57.1 +/- 4.0 mV, polarized to -72.7 +/- 4.5 mV with BAPTA-AM, an intracellular Ca(2+) chelator, and depolarized to -30.7 +/- 6.1 mV with thapsigargin, which mobilizes Ca(2+) from intracellular stores. With nystatin-perforated patch clamp, thapsigargin activated a current that reversed near the Cl(-) reversal potential, which was blocked by Cl(-) channel blockers, 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) and Zn(2+), by I(-) (10 mM), and by chlorotoxin (EC(50) = 47 nM). With conventional whole-cell clamp, NPPB- and Zn(2+)-sensitive currents became larger with increasing [Ca(2+)](i) (10, 150, 300 nM). Single-channel recordings of inside-out patches confirmed Ca(2+) sensitivity of the channel and showed open-state conductances of 40, 80, 130, and 180 pS, and outside-out patches confirmed sensitivity to chlorotoxin. In primary culture, small phase-dark NRAs developed into small GFAP-positive bipolar cells with chlorotoxin-sensitive Cl(Ca) channels. Imaging with biotinylated chlorotoxin confirmed the presence of label in GFAP-positive cells from regions of brain injury, but not from uninjured brain. Chlorotoxin-tagged cells isolated by flow cytometry and cultured up to two passages exhibit positive labeling for GFAP and vimentin, but not for prolyl 4-hydroxylase (fibroblast), A2B5 (O2A progenitor), or OX-42 (microglia). Expression of a novel chlorotoxin-sensitive Cl(Ca) channel in a morphologically distinct subpopulation of NRAs distinguishes these cells as a new subtype of reactive astrocyte.

Animals↗
PubMed2003

cGMP-dependent and not cAMP-dependent kinase is required for adenosine-induced dilation of intracerebral arterioles.

Adenosine (ADO) is a potent cerebral vasodilator and has been proposed as a metabolic regulator of cerebral blood flow. However, the signal transduction pathway by which ADO causes vasodilation in cerebral microvessels is currently unknown. The current study was designed to investigate the role of cyclic nucleotides and cyclic nucleotide-dependent protein kinases in ADO-induced dilation of resistance-sized rat cerebral arterioles that develop spontaneous tone. Arterioles were cannulated and perfused intraluminally at constant flow (2 microl/min) and pressure (60 mm Hg). ADO (29.7 +/- 2.0%; 1 microM), CGS-21680 (16 +/- 4%, 1 microM), 8-bromo-cyclic guanosine monophosphate (8 Br-cGMP; 29.9 +/- 3.9%; 100 microM), sodium nitroprusside (SNP; 30.6 +/- 3.3%, 1 microM), cyclic guanine monophosphate-dependent protein kinase activator (Sp-8-pCPT-cGMPS, 25.9 +/- 4.2%; 10 microM), forskolin (30.5 +/- 5.9%; 0.1 microM), and pH 6.8 all produced large dilations. The selective cGMP-dependent protein kinase inhibitor, Rp-8-pCPT-cGMPS (10 microM), had no effect on resting diameter or reactivity to acidic pH, but significantly ( < 0.05) attenuated arteriolar dilations to ADO (59%, n = 8), CGS-21680 (60%, n = 4), SNP (62%, n = 3), 8 Br-cGMP (88%, n = 3), and Sp-8-pCPT-cGMPS (98%, n = 3). H8, the less-selective cyclic nucleotide-dependent protein kinase inhibitor, had similar effects as Rp-8-pCPT-cGMPS. Additionally, the inhibitor of the soluble guanylate cyclase, 1H-[1,24]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ), blocked the response to SNP (70% inhibition) and significantly inhibited the ADO response (43% inhibition). In contrast, inhibition of the cyclic ADO monophosphate (cAMP)-dependent protein kinase Rp-8-CPT-cAMPS had no effect on the ADO, SNP, or pH responses, but significantly blocked forskolin-induced vasodilation (53%). It is concluded that ADO-induced vasodilation in cerebral microvessels, at least in part, involves cGMP and cGMP-dependent protein kinase, but not cAMP or cAMP-dependent kinase. Our data therefore provides a new insight into mechanisms by which ADO invokes vasodilation in cerebral microvascular arterioles.

Adenosine↗
PubMed2003

Concomitant boost of stratified target area with gamma knife radiosurgery: a treatment planning study.

Conventional Gamma Knife Stereotactic Radiosurgery (GKSRS) has been focused on delivering a single peripheral dose to the gross target volume based on the anatomic information derived from the magnetic resonance or computed tomography (CT) studies. In this study, we developed a treatment planning approach that allows a boost dose to be delivered concomitantly to the desired subtarget area while maintaining the peripheral isodose coverage of the target volume. The subtarget area is defined as the high-risk or the tumor burden areas based on the functional imaging information such as the magnetic resonance spectroscopy (MRS) studies or the physician's clinical diagnosis. Treatment plan comparisons were carried out between the concomitant boost plans and the conventional treatment plans using dose volume histogram (DVH), tissue volume ratio (TVR), and the maximum dose to the peripheral dose ratio (MD/PD) analysis. Using the concomitant boost approach, more conformal and higher dose was delivered to the desired subtarget area while maintaining the peripheral isodose coverage of the gross target volume (GTV). Additionally, the dose to the normal brain tissue was found to be equivalent between the concomitant boost plans and the conventional plans. As a result, we conclude that concomitant boost of a stratified target area is feasible for GKSRS.

Brain Neoplasms↗
PubMed2003

Adenosine-A2a receptor down-regulates cerebral smooth muscle L-type Ca2+ channel activity via protein tyrosine phosphatase, not cAMP-dependent protein kinase.

Adenosine acting via A2a receptors (A2aR) is a potent cerebral vasodilator that relaxes vascular smooth muscle cells (VSMCs) by a mechanism attributed to activation of cAMP-dependent protein kinase (cAK). We examined effects of adenosine and its mechanism of action on L-type Ca2+ channels in native VSMCs from rat basilar artery. Reverse transcription-polymerase chain reaction and immunofluorescence imaging confirmed transcription and expression of A2aR, and in situ hybridization confirmed presence of mRNA for L-type Cav1.2b channels. In patch-clamp experiments, adenosine down-regulated Ca2+ channel currents in a concentration-dependent manner, with receptor-subtype-specific antagonists [4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo-[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM-241385) versus 1,3-dipropyl-8-cyclopentyl-1,3-dipropylxanthine] showing that this was caused by action of A2aR. Down-regulation of channel currents was mimicked by stimulation of cGMP-dependent protein kinase (cGK; 8-Br-cGMP) and by inhibition of tyrosine kinase (AG-18) but not by stimulation of cAK [forskolin and 8-bromo-cAMP (8-Br-AMP)]. Down-regulation of currents by the A2aR agonist 2-[p-(2-carboxyeth yl)phenylethylamino]-5'-N-ethyolcarboxamidoadenosine (CGS-21680) was blocked by inhibiting protein tyrosine phosphatase (PTP; orthovanodate and dephostatin), but not by inhibiting cGK (KT-5823 and H-7). Western blots of lysate or of immunoisolated Ca2+ channels from arterial segments incubated with CGS-21680 showed 1) increased phosphorylation of vasodilator-stimulated phosphoprotein that was blocked by inhibiting cAK (KT-5720), consistent with activation of cAK by A2aR; and 2) decreased tyrosine phosphorylation of immunoisolated alpha1c subunit of the Ca2+ channel. Our data show that cAK, although activated, was not germane to down-regulation of Ca2+ channel activity by A2aR, and they delineate a novel signaling mechanism involving reduced tyrosine phosphorylation of Ca2+ channels by A2aR probably caused by PTP activation.

Animals↗
PubMed2003

Early pathophysiological changes in cerebral vessels predisposing to stroke.

We studied the early pathophysiological response of lenticulostriate arterioles in rats in three models of human conditions associated with stroke: (a) chronic angiotensin II-hypertension; (b) chronic nicotine administration; (c) oxidative endothelial injury. In all three models, quantitative patch clamp analysis of freshly isolated vascular smooth muscle cells from lenticulostriate arterioles and posterior cerebral arteries showed significant increases in activity of functional L-type calcium channels that were due to an increase in open channel probability, with no change in other biophysical properties or in channel expression. In addition, all three models showed evidence of endothelial dysfunction, but of a different nature in the three. With chronic angiotensin II-hypertension, but not in the other two models, endothelial nitric oxide synthase (eNOS) was dysfunctional, was mislocalized away from its normal abluminal location, and was accumulated in peri-nuclear Golgi. By contrast, the other two models showed no mislocalization of eNOS, but instead showed evidence of oxidative stress in endothelium, with up-regulation of superoxide dismutase and hexose kinase. All three models showed significant up-regulation of expression of proliferative cell nuclear antigen (PCNA) (PCNA index, 70-80%) in arterioles in situ, which is associated with increased activation of the nuclear transcription factor, phospho-cAMP response element binding protein (phospho-CREB). In addition, calmodulin-dependent protein (CaM) kinase II was activated, in concert with the activation of L-type calcium channels. Furthermore, blockers of either L-type calcium channels (amlodipine) or of CaM kinase II (KN-93) completely prevented the activation of CREB and the up-regulation of PCNA in arterioles. Our findings demonstrate that abnormal regulation of L-type calcium channels is directly responsible for abnormal proliferative responses in vascular smooth muscle in various forms of cerebral arteriolar injury associated with endothelial dysfunction.

Amlodipine↗
PubMed2002

Fetal and ovarian radiation dose in patients undergoing gamma knife radiosurgery.

BACKGROUND: It is difficult to estimate the fetal or ovarian radiation dosage for female patients undergoing Gamma Knife radiosurgery. Our goals are to determine the fetal and ovarian radiation dose at various distances from a cranial isocenter, to provide a reference for practitioners to estimate the fetal dose with respect to gestational age, and to identify the components of pelvic extracranial radiation. METHODS: An anthropomorphic phantom and ion chamber were used to measure the dose at 50, 60, and 70 cm from a cranial isocenter and at three points within the transverse plane for the supine position. Each measurement consisted of a 5-minute exposure. Additional measurements were taken for four collimator sizes, the prone position, off-axis, and with one-half of all collimator holes plugged. RESULTS: The values of the fetal and ovarian dose rates ranged from 0.27 cGy/min to 0.05 cGy/min based on distance from the isocenter. The fetal and ovarian dose can be up to 8.1 cGy for a 30-minute Gamma Knife treatment. The dose fell off more rapidly than predicted by the inverse square law. There was no dependence of fetal dose rate on collimator size. No advantage to the prone position could be shown. Leakage and collimator scatter are the main components of extracranial dose 50 to 70 cm from the isocenter. CONCLUSIONS: The fetal and ovarian dose is a function of treatment time and distance from the isocenter. We recommend pregnancy status assessment in women of reproductive age and treatment plan design using large volume shots in order to minimize treatment time.

Brain Neoplasms↗