Steven C. Quay

Renin synthesis by canine aortic smooth muscle cells in culture

Angiotensin-I generating activity has been detected in homogenates of arterial tissue but it remains unclear whether this enzymatic activity results from the presence of renin itself or from the action of other proteases such as cathepsin D. In an assay system employing anephric dog plasma as substrate and buffered to pH 7.4, we detected angiotensin-I generating activity in homogenates of canine aortic smooth muscle cells. This enzymatic activity was in large part inhibitable by renin-specific antisera raised to pure canine renal renin. Immunofluorescent study of cultured arterial smooth muscle cells was also performed using renin specific antiserum. Granular cytoplasmic immunofluorescence was detected when specific antirenin serum was used but not when preimmune serum was employed. The addition of pure canine renin to the renin antiserum during staining suppressed the granular immunofluorescence confirming the specificity of staining. Finally, biosynthetic radiolabelling studies were performed. Immunoprecipitation of newly synthesized proteins with antirenin serum and staphylococcal protein A followed by gel electrophoresis and autoradiography demonstrated the synthesis of an immunoreactive protein with the molecular weight of renin. Pretreatment of the antirenin serum with pure canine renin resulted in the disappearance of this immunoreactive protein band. Thus these studies provide multiple lines of evidence to indicate the in situ synthesis of renin by vascular smooth muscle cells.

Carcinosarcoma of the prostate: case report and review of the literature.

We report the third case of carcinosarcoma of the prostate. The epithelial element consisted of a highly malignant adenocarcinoma. The mesenchymal component was composed of malignant osteosarcoma and chondrosarcoma.

Papillary carcinoid tumor of the lung.

Carcinoid tumors of the lung have a wide histologic spectrum. The histologic differential diagnosis of papillary tumors in the lung generally does not include carcinoid. A carcinoid tumor that formed a discrete coin lesion on chest radiograph is presented in this report. On gross examination the center appeared and felt spongy. On microscopic examination delicate, compacted papillae were separated by a serpentine space continuous with air spaces at the periphery of the tumor. The papillae were each composed of a fibrovascular core, an undulating basement membrane separating stroma from epithelial cells, and cuboidal clear and dark cells that proved to be, respectively, healthy and degenerate cells of carcinoid tumor with neurosecretory granules. Upon the carcinoid cells, draped in the manner of an umbrella, were nonciliated, respiratory cells that proved to be Clara cells. The various histologic patterns of bronchopulmonary carcinoids and the differential diagnosis of papillary tumors within the lung are tabulated.

BINDING PROTEINS AND MEMBRANE TRANSPORTfn1

The recent studies have clearly established two types of active transport systems. One type is membrane-bound and can be observed in membrane vesicles and the other type is osmotic-shock-sensitive and requires binding proteins to produce active transport. It appears that the membrane-bound systems derive cellular energy from the energy-rich membrane state which can be formed from respiration or ATP-hydrolysis, while the binding protein systems are more directly coupled to phosphate bond energy derived from glycolysis or oxidative phosphorylation. The following conclusions concerning the role of the binding proteins are offered: 1. The binding proteins are present in relatively large amounts (approximately 10(-6) or 10%-5) M) and appear to reside in the periplasmic space. 2. They do not appear to be involved in solute translocation steps, although they cantain a second binding site that could interact with membrane components. 3. The binding proteins appear to increase the affinity of the transport system for the solute by interacting with a membrane component. This may substrate for the membrane transport system.

Isolation and Characterization of Membrane Binding Proteins

The term binding protein in the field of membrane transport refers to the group of relatively low molecular weight proteins possessing a reversible binding activity for solutes of specific transport systems. Most of these proteins have been isolated from gram-negative bacteria by a cold osmotic shock treatment. No enzymatic function has been demonstrated for these proteins. The mild shock treatment of gram-negative bacteria also removes the periplasmic enzymes (Heppel, 1971), so called because they appear to be located in the “periplasm,” i.e., the space between the cytoplasmic membrane and the cell wall (Mitchell, 1961). A large body of data has accumulated to suggest that the binding proteins act as the recognition site for active transport systems. Recent genetic evidence indicates that these proteins play a direct role in solute transport.

Regulation of Membrane Transport

The intracellular levels of most nutrients are carefully controlled to meet the varying demands for nutrients presented by the normal growth cycle of the cell. The cell must balance the increases in nutrient levels (such as, synthesis) with the decreases in these nutrients (metabolism or macromolecular synthesis). Active transport is usually characterized as a process that will increase the cellular level of a nutrient. Most transport processes, however, are reversible to some extent and serve for exit as well as entry of nutrients. In a facilitated diffusion system the influx and efflux capacities are equal. In ative transport systems the coupling of metabolic energy can lead to chemical gradients of transported solutes. Since transport activities alter the cellular levels of nutrients it is important that the cell have a way of regulating them. Regulation of the biosynthesis of various cellular nutrients has been extensively studied in the past, but regulation of transport systems has been largely ignored until recently.

Effect of manganese (II) bis(glycinate)dichloride on Ca2+ channel function in cultured chick atrial cells

Manganese (II) bis(glycinate)dichloride (Mn(glycinate)2) is a coordination complex of manganese with application as a contrast enhancement agent for magnetic resonance imaging in the heart. To determine the cardioactivity of the manganese ion in this chelation cage, the effects of Mn(glycinate)2 on Ca channel function in the cultured chick atrial cell was studied. Mn(glycinate)2 decreased amplitude of contraction in chick atrial cells from embryos 14 days in ovo with complete inhibition of beating at 1 mM and half-maximal effect at 0.1 mM. Under control conditions, Bay K 8644, a Ca channel activator increased amplitude of contraction by 86% with a half maximal effect at 3.2 x 10(-7) M. In the presence of 0.025 mM Mn(glycinate)2, a concentration which had no effect on the amplitude of contraction, the maximum response to Bay K 8644 was decreased to 31%. Mn(glycinate)2 had no effect on the EC50 for the response to Bay K 8644, 1.7 +/- 0.1 x 10(-9) M (S.E.M., n = 4) in control cells compared to 2.2 +/- 0.4 x 10(-9) M (S.E.M., n = 4) in cells incubated with Mn(glycinate)2. 45Ca2+ uptake over 5 min in cultured chick atrial cells decreased from 2.0 nmol/mg protein in control cells to 1.5 nmol/mg protein in the presence of 10(-5) M PN200-110, a Ca2+ channel blocker, a decrease of 28%. 45Ca2+ uptake decreased to 0.94 nmol/mg protein (53%) in the presence of 1 nmol Mn(glycinate)2. Effects of Mn(glycinate)2 and PN200 were not additive. These data demonstrate that Mn(glycinate)2 exerts its negative inotropic effect, at least partially, by interfering with the function of the L-type Ca channels at high concentrations.

Role of tRNA Leu in Branched-chain Amino Acid Transport

The intracellular levels of most nutrients are carefully controlled to meet the varying demands for these during the normal growth of the cell. To control the intracellular level of an amino acid, the cell must balance the processes that lead to increases in the nutrient concentration, such as transport and biosynthesis, with those that tend to decrease it, such as metabolism and macromolecular synthesis. The regulation of the levels of the branched-chain amino acids, leucine, isoleucine, and valine, in bacteria and mammalian cells has been the subject of numerous studies (for reviews, see Umbarger 1973; Quay and Oxender 1979, 1980). These studies indicate a complex system for regulation of biosynthesis and transport involving amino acids, tRNA molecules and their synthetases, transcriptional termination factors, and the products of structural genes for regulatory loci. This review discusses the experimental evidence that leads to the hypothesis that tRNA Leu is involved in branched-chain amino acid transport in both bacteria and mammalian cells. ROLE OF AMINOACYL-tRNA SYNTHETASES Aminoacyl-tRNA synthetases and their cognate tRNA species have been implicated in the regulation of amino acid biosynthetic enzymes for histidine (Brenner and Ames 1971), leucine (Low et al. 1971), isoleucine and valine (Umbarger 1973), arginine (Williams 1973), tryptophan (Bertrand et al. 1975), and methionine (Brenchley and Williams 1975). In a comprehensive study, the regulation of transport was tested in strains with mutations in the valyl-, isoleucyl-, and leucyl-tRNA synthetases to test whether these proteins were effectors in this regulation mechanism. Strain NP29 valS ts exhibits a temperature-sensitive phenotype that...