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Biomedical subjects

K Pritchard

Publications and source records attributed to K Pritchard.

At least 19 recordsLinked to original sources
PubMed1995

Caldesmon mRNA splicing and isoform expression in mammalian smooth-muscle and non-muscle tissues.

The recent determination of the genomic sequence of human caldesmon indicates that eight caldesmon mRNA species could be generated by selection of exon 1 or 1', exon 3a or 3ab and/or exon 4. We used reverse transcriptase PCR to determine which transcripts were produced in human, rabbit and sheep artery, vein, lung, intestine, kidney and liver. In all tissues the same three transcripts were present: exons 1'-2-3a-5-6...13, exons 1'-2-3a3b-5-6-...13 and exons 1'-2-3a3b-4-5-6...13. Exon 1 was not present and exon 4 was only present when exon 3b was also present. Three protein isoforms of caldesmon can be distinguished by electrophoresis on high-porosity 6% polyacrylamide gel: 130 kDa, 120 kDa and 70 kDa. The 70 kDa isoform lacks the sequence encoded by exon 3b. We investigated whether the two high-molecular-mass isoforms correspond to the presence and absence of exon 4 using an antiserum specific to the sequence encoded by exon 4. Western-blotting and immunoprecipitation experiments showed that both the 130 kDa and the 120 kDa isoforms were expressed with and without the exon 4 sequence. We therefore propose that the molecular-mass heterogeneity arises from additional first exons, possibly with separate promoter regions, which have not yet been characterized in the genomic sequence.

Animals↗
PubMed1994

Location of two contact sites between human smooth muscle caldesmon and Ca(2+)-calmodulin.

We measured Ca(2+)-calmodulin binding to expressed human caldesmon fragments by three techniques: tryptophan fluorescence enhancement, change in fluorescence of TA-calmodulin, and cosedimentation with calmodulin-Sepharose. Ca(2+)-calmodulin bound with similar affinity to peptide M73 (C714SMWEKGNVFSSPGF727, N terminus of domain 4b), to all the fragments of caldesmon containing this peptide, and also to H9 (Thr726-Val793), which did not contain this peptide (Kd = 0.2-0.8 microM). We conclude that Ca(2+)-calmodulin binds at two sites on caldesmon; site A is the sequence 715MWEKGNVFS723 previously identified by Zhan et al. (Zhan, Q., Wong, S. S., and Wang, C.-L.A. (1991) J. Biol. Chem. 266, 21810-21814), and site B is located nearer the C terminus of caldesmon. Ca(2+)-calmodulin binding at site B is coupled to reversal of caldesmon inhibition of actin-tropomyosin activated myosin MgATPase, while calmodulin binding at site A has no detectable function. H9 did not displace M73 from Ca(2+)-calmodulin, while the other fragments did. High concentrations of M73 (> 1000 x Kd) could not displace H9 bound to Ca(2+)-calmodulin-Sepharose. Thus sites A and B in calmodulin are functionally separate. Analysis of overlapping expressed fragments indicates that site B is located in the sequence Thr726-Leu767, which includes Trp749. The minimal Ca(2+)-calmodulin binding sequence could be 744SRINEWLTK752.

Actins↗
PubMed1994

Filamin and gelsolin influence Ca(2+)-sensitivity of smooth muscle thin filaments.

Sheep aorta thin filaments were prepared by ultracentrifugation of an ATP-containing extract in the presence of different concentrations of ethanediol. Thin filaments prepared without ethanediol contained small quantities of tropomyosin (0.027 Tm:actin) and caldesmon (0.017 CD:actin) and activated the MgATPase of skeletal myosin independently of Ca2+. Ultracentrifugation in the presence of 10-20% ethanediol resulted in preparation of thin filaments with increased content of tropomyosin (0.17 Tm:actin) and caldesmon (0.04 CD:actin). These thin filaments possessed high Ca(2+)-sensitivity in activation of skeletal muscle myosin ATPase. Besides actin, tropomyosin and caldesmon, thin filaments contained gelsolin and filamin. Gelsolin content (0.007 gelsolin:actin) was independent of the presence of ethanediol. The filamin content decreased from 0.015 to 0.007 mol:mol actin when the ethanediol concentration was increased from 0 to 20%, and was negatively correlated with the Ca2+ sensitivity of thin filaments. In a reconstituted system, pure filamin or gelsolin affected caldesmon regulation of actomyosin ATPase. Gelsolin (0.01:actin) reduced the inhibition of actomyosin ATPase caused by caldesmon and increased the potency of Ca(2+)-calmodulin in reversing this inhibition. Filamin (0.007:actin) also decreased the inhibitory action of caldesmon on actin-activated myosin ATPase and also potentiated the reversal of this inhibition by calmodulin. We conclude that minor components of smooth muscle thin filaments (gelsolin and filamin) significantly modify caldesmon mediated regulation of actomyosin ATPase. We suggest a tropomyosin-mediated mechanism by which filamin or gelsolin could exert similar effects.

Actin Cytoskeleton↗
PubMed1994

Changes in the caldesmon isoform content and intimal thickening in the rabbit carotid artery induced by a silicone elastomer collar.

The presence of a silicone elastomer collar around one carotid artery of a rabbit induces thickening of the tunica intima. We used immunoblotting to study quantitatively changes in the isoforms of caldesmon, a protein implicated in the regulation of contractility in smooth muscle, while also monitoring the histological changes during 28 days after collaring. Control rabbit carotid arteries (n = 28) contained 245 +/- 6.4 nmol/g protein of the larger isoform of caldesmon (CDh) and 68.3 +/- 3.6 nmol/g protein of the smaller isoform (CD1). Four days after collaring, intimal thickening was slight, but 44% of arterial CDh had been lost; this loss of CDh was therefore from the tunica media. At 10 days, CDh fell to 37% of the control level. Immunofluorescence using CDh-specific antibodies showed that the CDh level was diminished but remained uniform across the wall of collared arteries. At 14 days, when intimal thickening was maximal, there was 30% more CD1 than in controls. At 28 days, the neointima had thinned, and CD1 had fallen to below control levels. Thus, CD1 levels reflected the development and regression of neointima. Changes in caldesmon isoforms showed that smooth muscle cell phenotypic changes occurred throughout the arterial wall.

Animals↗
PubMed1994

Chronic exercise in dogs increases coronary vascular nitric oxide production and endothelial cell nitric oxide synthase gene expression.

Recently, we have shown that chronic exercise increases endothelium-derived relaxing factor (EDRF)/nitric oxide (NO)-mediated epicardial coronary artery dilation in response to brief occlusion and acetylcholine. This finding suggests that exercise can provide a stimulus for the enhanced production of EDRF/NO, thus possibly contributing to the beneficial effects of exercise on the cardiovascular system. Therefore, the purpose of the present study was to examine whether chronic exercise could influence the production of NO (measured as the stable degradation product, nitrite) and endothelial cell NO synthase (ECNOS) gene expression in vessels from dogs after chronic exercise. To this end, dogs were exercised by running on a treadmill (9.5 km/h for 1 hour, twice daily) for 10 days, and nitrite production in large coronary vessels and microvessels and ECNOS gene expression in aortic endothelial extracts were assessed. Acetylcholine (10(-7) to 10(-5) mol/L) dose-dependently increased the release of nitrite (inhibited by nitro-L-arginine) from coronary arteries and microvessels in control and exercised dogs. Moreover, acetylcholine-stimulated nitrite production was markedly enhanced in large coronary arteries and microvessels prepared from hearts of dogs after chronic exercise compared with hearts from control dogs. One potential mechanism that may contribute to the enhanced production of nitrite in vessels from exercised dogs may be the induction of the calcium-dependent ECNOS gene. Steady-state mRNA levels for ECNOS were significantly higher than mRNA levels for von Willebrand's factor (vWF, a specific endothelial cell marker) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH, a constitutively expressed gene) in exercised dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Oxidoreductases↗
PubMed1993

The fine structure of the human endometrial glandular epithelium in cases of unexplained infertility: a morphometric study.

In the present study attempts have been made to express in quantitative terms the fine structure of the endometrial glandular epithelium in well-timed biopsies from fertile women during the early luteal phase. Biopsies from women with unexplained infertility have also been examined. Certain abnormalities of glandular maturation were found in these women. The nuclear channel system was not present at day luteinizing hormone (LH) + 4 in the infertile group while at LH + 6 there were more cells containing this feature than seen in the fertile group. There also seem to be abnormalities associated with intracellular deposits of glycogen-rich material and mitochondrial elaboration in the infertile women. Changes in the secretory apparatus and rough endoplasmic reticulum were observed. The evidence from the present study suggests that the endometria in the examined group of infertile women is responsive to steroidal stimulation. This response however, may be delayed or inadequate.

Cell Nucleus↗
PubMed1993

The Canadian experience with intensive fluorouracil, epirubicin and cyclophosphamide in patients with early stage breast cancer.

A multicentre dose-finding pilot study was conducted to determine an intensive regimen of fluorouracil (F), epirubicin (E) plus cyclophosphamide (C) [FEC] that was tolerable and acceptable to patients with node-positive operable (n = 266) or locally advanced (n = 22) breast cancer. Consecutive patients were treated with fluorouracil and epirubicin administered intravenously on days 1 and 8, in addition to cyclophosphamide orally for 14 days. Chemotherapy cycles were repeated at monthly intervals for 6 months, and dosages were increased according to a predetermined protocol. End-points were hospital admissions due to febrile neutropenia and changes in cardiac function as assessed by radionuclide angiography. The first 46 patients were treated with doses of F = 375 mg/m2, E = 50 mg/m2 and C = 75 mg/m2 (level 1), then 42 patients received F = 500 mg/m2, E = 50 mg/m2 and C = 75 mg/m2 (level 2), 69 patients received F = 500 mg/m2, E = 60 mg/m2 and C = 75 mg/m2 (level 3), and 42 patients received F = 500 mg/m2, E = 70 mg/m2 and C = 75 mg/m2 with concurrent antibiotics (level 4). Rates of febrile neutropenia were 8.7% (level 1), 7.1% (level 2), 18.8% (level 3), and 31% (level 4) [p = 0.002]. Accrual to level 4 was discontinued according to study protocol and a further 89 patients were recruited at level 3 dosages with antibiotic prophylaxis (level 3a), resulting in a 5.6% rate of febrile neutropenia. The difference in febrile neutropenia rates between dosage levels 3 and 3a was statistically significant (p = 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1992

A pilot study of intensive cyclophosphamide, epirubicin and fluorouracil in patients with axillary node positive or locally advanced breast cancer.

A multicentre pilot study has been conducted to determine an intensive regimen of cyclophosphamide, epirubicin, and fluorouracil which was tolerable and acceptable to patients with node positive breast cancer. Consecutive patients with operable axillary node positive breast cancer (T1-3, N1-2, M0), 266 patients, or locally advanced breast cancer (T4), 22 patients, were treated with cyclophosphamide post-operatively for 14 days and epirubicin and fluorouracil, both intravenously on days 1 and 8. Each cycle was repeated monthly for 6 months. Dosages were increased according to predetermined guidelines. Outcome measures were admission to hospital for febrile neutropenia and change in cardiac function as assessed by radionuclide angiography. The first 46 patients were treated at the doses of cyclophosphamide = 75 mg/m2, epirubicin = 50 mg/m2, fluorouracil = 375 mg/m2 (level 1), then 42 patients at cyclophosphamide = 75 mg/m2, epirubicin = 50 mg/m2 and fluorouracil = 500 mg/m2 (level 2), 69 patients at cyclophosphamide = 75 mg/m2, epirubicin = 60 mg/m2, and fluorouracil = 500 mg/m2 (level 3), and 42 patients at cyclophosphamide = 75 mg/m2, epirubicin = 70 mg/m2, and fluorouracil = 500 mg/m2 with concurrent antibiotics (level 4). The rates of febrile neutropenia were 8.7% (level 1), 7.1% (level 2), 18.8% (level 3), and 31% (level 4), respectively, P = 0.002. Accrual to level 4 was discontinued according to study guidelines and a further 89 patients were recruited at level 3 dosages with antibiotic prophylaxis (level 3a), resulting in a 5.6% rate of febrile neutropenia. The difference in febrile neutropenia rates between levels 3 and 3a was statistically significant. There were no toxic deaths and 2 cases of heart failure. In conclusion, through a careful dose-finding study in patients with operable or locally advanced breast cancer, an intensive epirubicin-containing adjuvant regimen has been established which is presently being compared with standard CMF (cyclophosphamide, methotrexate, 5-fluorouracil) chemotherapy in a randomised trial. In addition, this study suggests that antibiotic prophylaxis reduces the risk of febrile neutropenia in breast cancer patients receiving intensive chemotherapy.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1991

Ca(2+)-dependent regulation of vascular smooth-muscle caldesmon by S.100 and related smooth-muscle proteins.

1. We have investigated the ability of bovine brain S.100, and of three related proteins from sheep aorta smooth muscle, to confer Ca(2+)-sensitivity on thin filaments reconstituted from smooth-muscle actin, tropomyosin and caldesmon. 2. At 37 degrees C in pH 7.0 buffer containing 120 mM-KCl, approximately stoichiometric amounts of S.100 reversed caldesmon's inhibition of the activation of myosin MgATPase by smooth-muscle actin-tropomyosin. The [S.100] which reversed by 50% the inhibition by caldesmon (the E.C.50) was 2.5 microM when [caldesmon] = 2-3 microM in the assay mixture. When [KCl] was decreased to 70 mM, E.C.50 = 11.5 microM; at 25 degrees C in 70 mM-KCl, up to 20 microM-S.100 had no effect. When skeletal-muscle actin rather than smooth-muscle actin was used to reconstitute thin filaments, 20 microM-S.100 did reverse inhibition by caldesmon, at 25 degrees C in buffer containing 70 mM-KCl. This dependence on conditions is also characteristic of the calmodulin-caldesmon interaction. 3. These results suggested that S.100 or a related protein might interact with caldesmon in smooth muscle. We therefore attempted to prepare such a protein from sheep aorta. Three proteins were purified: an Mr-17,000 protein (yield 16 mg/kg), an abundant Mr-11,000 protein (yield 48 mg/kg), and an Mr-9000 protein (yield 4 mg/kg). Neither of the last two low-Mr proteins had any effect on activation of myosin MgATPase by reconstituted thin filaments. The protein of Mr 17,000 had Ca(2+)-sensitizing activity, and behaved exactly like brain calmodulin in the assay system.

Actin Cytoskeleton↗
PubMed1989

Ca2+-calmodulin binding to caldesmon and the caldesmon-actin-tropomyosin complex. Its role in Ca2+ regulation of the activity of synthetic smooth-muscle thin filaments.

We measured the concentration of calmodulin required to reverse inhibition by caldesmon of actin-activated myosin MgATPase activity, in a model smooth-muscle thin-filament system, reconstituted in vitro from purified vascular smooth-muscle actin, tropomyosin and caldesmon. At 37 degrees C in buffer containing 120 mM-KCl, 4 microM-Ca2+-calmodulin produced a half-maximal reversal of caldesmon inhibition, but more than 300 microM-Ca2+-calmodulin was necessary at 25 degrees C in buffer containing 60 mM-KCl. The binding affinity (K) of caldesmon for Ca2+-calmodulin was measured by a fluorescence-polarization method: K = 2.7 x 10(6) M-1 at 25 degrees C (60 mM-KCl); K = 1.4 x 10(6) M-1 at 37 degrees C in 70 mM-KCl-containing buffer; K = 0.35 x 10(6) M-1 at 37 degrees C in 120 mM-KCl- containing buffer (pH 7.0). At 37 degrees C/120 mM-KCl, but not at 25 degrees C/60 mM-KCl, Ca2+-calmodulin bound to caldesmon bound to actin-tropomyosin (K = 2.9 x 10(6) M-1). Ca2+ regulation in this system does not depend on a simple competition between Ca2+-calmodulin and actin for binding to caldesmon. Under conditions (37 degrees C/120 mM-KCl) where physiologically realistic concentrations of calmodulin can Ca2+-regulate synthetic thin filaments, Ca2+-calmodulin reverses caldesmon inhibition of actomyosin ATPase by forming a non-inhibited complex of Ca2+-calmodulin-caldesmon-(actin-tropomyosin).

Actins↗
PubMed1989

Correlation of blood pressure in normotensive and hypertensive individuals with platelet but not lymphocyte intracellular free calcium concentrations.

1. Fifty-two normotensive and essential hypertensive subjects were studied. Intracellular free calcium concentration [( Ca2+]i) was measured in lymphocytes (37 subjects) and platelets (18 subjects) by means of the fluorescent indicators, quin 2 and fura-2. In 31 subjects, plasma ionized calcium concentration was also measured. 2. There was a positive correlation between platelet [Ca2+]i and systolic blood pressure (r = 0.485, P less than 0.05), diastolic blood pressure (r = 0.542, P less than 0.02) and mean blood pressure (r = 0.534, P less than 0.02). 3. No statistically significant relationship was observed between plasma ionized calcium and blood pressure. 4. No relationship was found between lymphocyte [Ca2+]i and blood pressure, or between lymphocyte [Ca2+]i and plasma ionized calcium. 5. There was no relationship between [Ca2+]i of lymphocytes and platelets measured simultaneously from the same subject. 6. These findings reconcile previous conflicting reports and show a relationship between platelet but not lymphocyte [Ca2+]i and blood pressure in man.

Adult↗
PubMed1987

The mechanism of Ca2+ regulation of vascular smooth muscle thin filaments by caldesmon and calmodulin.

The interactions of vascular smooth muscle caldesmon with actin, tropomyosin, and calmodulin were determined under conditions in which the four proteins can form reconstituted Ca2+-sensitive smooth muscle thin filaments. Caldesmon bound to actin in a complex fashion with high affinity sites (K = 10(7) M-1) saturating at a stoichiometry of 1 per 28 actins, and lower affinity sites at 1 per 7 actins. The affinity of binding was increased in the presence of tropomyosin, and this could be attributed to a direct interaction between caldesmon and tropomyosin which was demonstrated using caldesmon cross-linked to Sepharose. In the presence of tropomyosin, occupancy of the high affinity sites was associated with inhibition of actin-activated myosin MgATPase activity. Caldesmon was found to bind to calmodulin in the presence of Ca2+, with an affinity of 10(6) M-1. The binding of Ca2+ X calmodulin to caldesmon was associated with the neutralization of inhibition of actin-tropomyosin. Ca2+ X calmodulin binding reduced but did not abolish the binding of caldesmon to actin-tropomyosin. From this data we have proposed a model for smooth muscle thin filaments in which Ca2+ regulates activity by converting the inhibited actin-tropomyosin-caldesmon complex to the active complexes, actin-tropomyosin-caldesmon-calmodulin X Ca2+ and actin-tropomyosin.

Actin Cytoskeleton↗
PubMed1987

Evidence for Na+/Ca2+ exchange in isolated smooth muscle cells: a fura-2 study.

Isolated smooth muscle cells (SMC) from guinea pig taenia coli were employed. Suspension of cells were externally loaded in saline with the fluorescent calcium indicators quin-2/AM or fura-2/AM at 20-40 microM or 4 microM respectively, resulting in an estimated intracellular concentration of 100-200 microM for quin-2 or 10-20 microM fura-2 (free acid). On addition of 100 microM carbachol or high K+o (80 mM) depolarization, fura-2 loaded cells contracted (104 +/- 47 micron, n = 121 rest: 39 +/- 13 micron, n = 59 contracted) identically to control (103 +/- 35 micron, n = 232 rest: 39 +/- 16 micron, n = 89 contracted) cells, whereas quin-2 loaded cells were unresponsive to these protocols and there was no significant length change. The Ca2+i of fura-2 loaded cells was 100 +/- 18 nM (mean +/- SD, n = 15) and was not significantly different from quin-2 loaded cells 107 +/- 26 nM (n = 13). Treatment of fura-2 loaded cells with 100 microM ouabain saline for 10-60 min progressively elevated the Ca2+i to a mean of 266 +/- 83 nM (n = 15). Reduction of Na+o (96% Li+ replaced) significantly increased Ca2+i to 317 +/- 77 nM (n = 8). After pretreatment with ouabain (100 microM), Na+o replacement (Li+) increased Ca2+i at a significantly faster rate [3.6 nM min-1 (control) cf. 19.8 nM min-1 (ouabain)].

Animals↗
PubMed1986

Na+/Ca2+ exchange in isolated smooth muscle cells demonstrated by the fluorescent calcium indicator fura-2.

Fura-2, a novel fluorescent indicator of cytoplasmic calcium concentrations ([Ca2+i]), was 'loaded' into smooth muscle cells isolated from guinea pig taenia coli. Resting cells maintained a stable [Ca2+i] of 107 +/- 26 nM (n = 13), which could be perturbed with ionomycin. [Ca2+i] was elevated by stimulation of the cells with carbachol or 50 mM KCl. Reduction of the plasmalemmal Na+ concentration gradient by inhibition of the Na+/K+-ATPase with ouabain markedly elevated [Ca2+i]; this elevation was dependent on extracellular Ca2+. [Ca2+i] was also increased by replacement of the extracellular Na+ with an organic cation.

Animals↗
PubMed1986

Caldesmon: a calmodulin-binding actin-regulatory protein.

The protein caldesmon, originally isolated from smooth muscle tissue where it is the most abundant calmodulin-binding protein, has since been shown to have a wide distribution in actin- and myosin- containing cells where it is localized in sub-cellular structures concerned with motility, shape changes and exo- or endo-cytosis. Caldesmon is believed to be an actin- regulatory protein, and binds with high affinity to actin or actin-tropomyosin. Caldesmon inhibits the activation by actin-tropomyosin of myosin MgATPase activity, and the inhibition can be reversed by Ca2+.calmodulin. The binding of caldesmon to smooth muscle proteins has been studied in detail, enabling a model to be constructed which could account for the observed Ca2+ regulation of smooth muscle thin filaments. The abundance of caldesmon, and the Ca2+-regulation of its activity via calmodulin, mean that it is potentially an important intracellular regulator of processes such as smooth muscle contraction, cell motility and secretion.

Actins↗
PubMed1986

Phase II study of lonidamine in patients with metastatic breast cancer: a National Cancer Institute of Canada Clinical Trials Group Study.

The National Cancer Institute of Canada Clinical Trials Group conducted a phase II study of lonidamine, given in an escalating oral daily schedule to a maximum dose of 450 mg/m2 in patients with previously treated advanced breast cancer. Five responses were seen in 30 evaluable patients (17%). Treatment was discontinued because of toxicity in seven patients. Toxicity generally consisted of myalgia, nausea, vomiting, skin hyperesthesia, somnolence, and ototoxicity. All side effects were reversible and no hematologic toxicity was observed. The absence of myelosuppression and the suggestive lack of cross-resistance between lonidamine and standard chemotherapeutic drugs warrant further studies of lonidamine in breast cancer, particularly in combination with other agents.

Adult↗