To study the mechanism of action of calcium channel-blocking drugs in intact, functioning myocardial tissue under physiological conditions, we related the inhibition of contraction of spontaneously beating monolayers of cultured chick embryo ventricular cells to studies of binding of four calcium channel-blocking drugs to the same preparation under the same physiological conditions. Nitrendipine produced a concentration-dependent decrease in amplitude of contraction (IC50 = 23 nM) as determined by a computer-assisted optical-video system. Studies using [3H]nitrendipine and equilibrium-binding techniques revealed a high affinity binding site in ventricular homogenates (KD = 0.15 nM) and on intact cultured heart cells (KD = 0.26 nM, Bmax = 51 fmol/mg of protein). These dissociation constants are similar to those reported by other workers for ventricular homogenates, but 100-fold lower than the IC50 for the negative inotropic effect in intact cells. Computer analysis of displacement of [3H]nitrendipine by unlabeled nitrendipine yielded a slope factor of 0.76 and identified an additional low affinity binding site for nitrendipine with KD = 19 nM, in good agreement with the IC50 for inhibition of contraction. Verapamil partially interacted with nitrendipine binding, whereas diltiazem showed no interaction. We conclude that, in intact myocardial cells, there are two classes of binding sites for nitrendipine; interaction of dihydropyridines with the low affinity site appears to mediate their effects on contractile function.

Animals↗

PubMed1982

Physicochemical characterization of ten fractions of bovine alpha lipoproteins.

With the onset of milk production, serum concentrations of alpha lipoproteins in the dairy cow steadily increase, frequently attaining values greater than 1.5 g/dl. Since these lipoproteins comprise a highly polydisperse system, we have carried out studies to explore differences among bovine alpha lipoproteins in the density interval between 1.05 to 1.21 g/ml. Separation into ten fractions was achieved ultracentrifugally in an isopycnic gradient. Agarose gel electrophoresis showed that all but the bottom fraction contained alpha lipoproteins as either the major or sole lipoprotein class. Compositional analyses revealed an increasing percentage of both protein and phospholipid and a decreasing percentage of cholesterol with increasing fraction density. The esterified to unesterified cholesterol ratio ranged from 3 to 8 from the top to the bottom of the gradient. The densities of the particles obtained from the various fractions were calculated both from sedimentation velocity measurements and from compositional analyses. The resulting density values agreed well with the solution densities of these isopycnic gradient fractions. The major apoprotein of each fraction was apoA-I. Combining diffusion coefficient data obtained by intensity fluctuation spectroscopy with sedimentation velocity data, we were able to calculate molecular weights, frictional ratios, and Einstein-Stokes radii for three of the fractions. Results are discussed in terms of previously published data on bovine lipoproteins as well as other mammalian data.

Animals↗

PubMed1981

5-Fluoro-2'-deoxyuridine incorporation in L1210 DNA.

We have employed cesium sulfate density gradient centrifugation to separate RNA and DNA of L1210 cells labeled with [3H]fluorodeoxyuridine. We have analyzed nucleotide and nucleoside digests of purified DNA from the [3H]fluorodeoxyuridine-labeled cells and demonstrate by reverse phase and anion exchange high pressure liquid chromatography the presence of tritium radioactivity co-migrating with fluorodeoxyuridine 5'-monophosphate or fluorodeoxyuridine. These observations demonstrate the internucleotide incorporation of fluorodeoxyuridine in DNA and suggest a new mechanism of action for this cytotoxic and mutagenic agent.

Animals↗

PubMed1981

Synergistic effects with inhibitors of de novo pyrimidine synthesis, acivicin, and N-(phosphonacetyl)-L-aspartic acid.

Acivicin, an inhibitor of L-glutamine-dependent amidotransferases, is active against the murine L1210 and P388 leukemia models. Cytidine triphosphate synthetase has been proposed as the primary target for this agent. Our results demonstrate that Acivicin is also an inhibitor of de novo pyrimidine biosynthesis. This inhibition results in the depletion of pyrimidine deoxyribonucleoside triphosphate pools and explains the effect of this agent on DNA synthesis. Further, Acivicin is synergistic with N-(phosphonacetyl)-L-aspartic acid, another inhibitor of de novo pyrimidine synthesis. The combination of these agents results in a more than additive depletion of deoxycytidine triphosphate pools which may account for their synergism in inhibiting cellular growth. Thus, the inhibition of de novo pyrimidine synthesis by Acivicin may be useful in modulating the effects of certain antimetabolites or other inhibitors of this pathway.

Animals↗

PubMed1979

Myeloma proteins from NZB and BALB/c mice: structural and functional differences.

Structural and functional analyses of myeloma immunoglobulins from inbred BALB/c mice and humans have provided important insights into the structure of the antibody molecule and the expression and evolution of antibody genes. One important question concerning these analyses is whether the myeloma process selects, in a nonrandom manner, the lymphocytes to be transformed. The availability of myeloma tumors in a second inbred strain of mouse, NZB, permits us to approach this question. In this respect. the NH2-terminal amino acid sequences of 27 kappa light chains as well as data relating to the antigen-binding properties and immunoglobulin class distribution of NZB myeloma proteins are presented and compared with similar data from the BALB/c mouse. These studies suggest that the myeloma proteins from the BALB/c and NZB mice constitute two populations of immunoglobulins with distinct functional and structural properties. The implication of this observation are discussed.

Amino Acid Sequence↗

PubMed1979

Comparisons of myeloma proteins from NZB and BALB/c mice: structural and functional differences of heavy chains.

The N-terminal sequences from heavy variable regions of 47 myeloma proteins of the NZB mouse have been analyzed. Sixteen of these VH regions have unblocked alpha amino groups and have been analyzed over their N-terminal 20 residues by automatic sequence analysis. These sequence data along with the antigen-binding profiles and immunoglobulin class distribution are compared with comparable data from BALB/c myeloma proteins. These comparisons suggest that the NZB and BALB/c populations of myeloma proteins are distinct from one another. The genetic implications of this conclusion are discussed.

Amino Acid Sequence↗

PubMed1978

Molecular weight distributions of polydisperse systems: application to very low density lipoproteins.

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Humans↗

PubMed1977

The structure and genetics of mouse immunoglobulins: an analysis of NZB myeloma proteins and sets of BALB/c myeloma proteins binding particular haptens.

Explore the source record for details and available documents.

Amino Acid Sequence↗

PubMed1975

Structure and regulation of immunoglobulins: kappa allotypes in the rat have multiple amino-acid differences in the constant region.

Immunoglobulin kappa chains from various inbred strains of rats have two serologically detectable forms that segregate in a Mendelian fashion (allotypes a and b of the RI-I locus). Partial amino-acid sequences from the constant regions of these two forms have been compared. Of the 81 residues of the constant region studied, 10 amino-acid substitutions as well as one size difference (sequence gap) were found. This large number of sequence differences among alternative forms of the kappa allotype raises provocative questions as to the genetic and evolutionary implications of these light chain allotypes. We designate allotypes whose alternative forms differ at multiple residue positions as complex allotypes. There are basically two genetic models that might explain complex allotypes. First, these allotypes are alleles of a single structural gene with an unusual evolutionary history. Second, all rats have genes that code for each of the light chain allotypes and a control mechanism that permits them to be expressed so that they mimic a Mendelian pattern of segregation. We discuss evidence from other immunoglobulin systems that is compatible with this second model.

Alleles↗

PubMedDate not supplied

Rearrangement of genetic information may produce immunoglobulin diversity.

The nearly complete amino-acid sequences of 22 closely related immunoglobulin kappa variable (Vkappa) regions from the inbred NZB mouse are presented. This group of Vkappa regions is encoded by at least six germline Vkappa genes. These data also suggest that the mouse kappa gene is divided into three segments termed V or variable (residues 1 to 98 or 99), J or joining (residues 99 or 100 to 112) and C or constant (residues 113--219). Tonegawa et la. have recently described a similar J segment for mouse lambda chains. Inbred mice contain multiple Vkappa and Jkappa gene segments. Therefore, different combinations of V and J gene segments may be joined at the DNA level during the differentiation of individual lymphocytes to contribute to antibody diversity.

Amino Acid Sequence↗

PubMedDate not supplied

Phase II study of tirapazamine plus cisplatin in patients with advanced or recurrent cervical cancer.

The aim of this study was to evaluate the activity and toxicity of a tirapazamine (TPZ)/cisplatin drug combination in patients with stage IV or recurrent cervical cancer. The chemotherapy was administered for a maximum of eight cycles every 21 days. TPZ was administered intravenously at 330 mg/m(2) over a 2-h infusion, followed 1 h later by cisplatin intravenously at 75 mg/m(2) over 1 h on day 1. All patients received antiemetics including dexamethasone, ondansetron, and lorazepam. Subsequent doses were unchanged, reduced, or omitted according to observed toxicity and protocol guidelines. Response evaluation was performed every two cycles. Thirty-six patients with stage IV or recurrent cervical cancer were treated. Ninety-four percent of patients had prior radiotherapy. Two patients had prior chemotherapy. There were two complete responses and eight partial responses (27.8%). An additional 11 patients (30.6%) had stable disease as their best response. Response rate was greater in tumors outside of the previously radiated field (44.4% vs 11.1%). The median time to progression was 32.7 weeks. The most frequent grade 3 or 4 adverse events were nausea, vomiting, and fatigue, which occurred in 30.6%, 25%, and 22% of subjects, respectively. Anemia was the most frequent grade 3 or 4 hematologic toxicity at 8.3%. We conclude that the combination of cisplatin and TPZ was reasonably well tolerated in patients with recurrent or advanced cervical cancer. Further evaluation of this drug combination may be warranted.

Adult↗

PubMedDate not supplied

Cardiac resynchronization: a novel therapy for heart failure.

Despite advances in medical therapy for patients with congestive heart failure, morbidity and mortality remain high. Conduction abnormalities, such as left bundle branch block, right bundle branch block, and nonspecific conduction delay, are observed commonly in patients with dilated cardiomyopathy. In patients with heart failure, the presence of intraventricular conduction delay is associated with more severe mitral regurgitation and worsened left ventricular systolic and diastolic function, and is an independent risk factor for increased mortality. Conventional dual-chamber (right atrial and right ventricular) pacing with a short atrioventricular delay was initially introduced as therapy for patients with advanced congestive heart failure to improve diastolic dysfunction and reduce mitral regurgitation. The acute beneficial hemodynamic effects observed in early, uncontrolled studies were not confirmed in subsequent randomized, controlled studies with longer follow-up. Cardiac resynchronization with novel biventricular (left and right ventricular) pacing systems has resulted in hemodynamic and functional benefits in patients with congestive heart failure and an underlying intraventricular conduction delay. Improvements in cardiac index, systolic blood pressure, and functional class have been reported with biventricular pacing, both acutely and at more than 1 year of follow-up. These encouraging preliminary results with biventricular pacing in patients with congestive heart failure will be validated in two prospective, randomized, controlled trials, Multicenter InSync Randomized Clinical Evaluation (MIRACLE) and Comparison of Medical Therapy, Pacing, and Defibrillation in Chronic Heart Failure (COMPANION). These studies are designed to evaluate the long-term efficacy of biventricular pacing in improving exercise capacity and in reducing morbidity and mortality in patients with advanced, symptomatic congestive heart failure. (c)2001 by CHF, Inc.

Journal Article↗