Action of the cardiac alpha 1-adrenergic receptor. Activation of cyclic AMP degradation

Using purified rat ventricular myocytes and membranes prepared from them, we have previously found that alpha 1-adrenergic stimulation causes decreased cyclic AMP accumulation and decreased activation of cyclic AMP-dependent protein kinase. We have now analyzed the mechanism by which alpha 1 stimulation is linked to cyclic AMP metabolism. In an adenylate cyclase assay in which carbachol inhibits the stimulatory effect of norepinephrine, the addition of prazosin (alpha 1-antagonist) has no effect on the response to norepinephrine. In membranes prepared from myocytes treated with pertussis toxin, norepinephrine competes for alpha 1-receptors (assessed by [3H]prazosin binding) with two components, binding to the high affinity component being sensitive to exogenous GTP, exactly as in membranes prepared from control myocytes. In intact cells labeled with [3H]adenine in which carbachol antagonizes the norepinephrine response, prazosin enhances accumulation of [3H]cyclic AMP due to norepinephrine. Treatment of cells with pertussis toxin eliminates inhibition by carbachol but does not alter prazosin's capacity to enhance the norepinephrine response. Addition of phosphodiesterase inhibitors eliminates this effect of alpha 1 blockade. In [3H]adenine-labeled cells loaded with [3H]cyclic AMP by prior treatment with isoproterenol, alpha 1-adrenergic stimulation enhances disappearance of [3H]cyclic AMP. Measurements of cellular cyclic AMP give results similar to those obtained with the adenine labeling technic. We conclude that occupation of the myocyte alpha 1-receptor results in stimulation of cyclic AMP phosphodiesterase activity.     

Morphological characteristics of testicular tissue in animals subjected to unilateral laser castration

In this paper, results of the morphological studies of mammalian testicular tissue after exposure of one of the testes to powerful laser radiation are reported. The results obtained are compared with those reported in the literature on the biological effect of penetrating radiation. No negative influence of powerful laser radiation is registered at the organism level. The criteria for estimation are the tissue response, morphological picture of spermatogenesis, and reproductive functions of exposed animals and of their progeny.     

Formal kinetic treatment of the possible role of proteins in DNA radiation tolerance, protection and sensitization

The formal-kinetic calculations have been made of the postirradiation behaviour of a "protein-DNA" water system with marked variations in protein and DNA concentrations. Protein is a strong competitive acceptor of active products of radiolysis of water and free radicals of DNA. The radioresistance of DNA in such a system and the influence of mercaptoethylamine, sensitizers and oxygen on DNA injury are discussed. The results of the calculations are compared with the data on the composition of cell nuclei and the data on the comparative radioresistance of cells, cell cycle, protective effects, and sensitization. In most cases, the results of the calculations do not contradict the experimental data. It is assumed that the protein protection may be the major factor in considering the endogenous radioresistance.     

Radiosensitivity during the irradiation of animals in an altered gaseous environment. A comparative study on mice and rats of the radiation-protective effect of oxygen-deficient gas mixtures

The radioprotective effect of gas hypoxic mixtures containing 5, 7, 8, 10 and 15% of oxygen on mice and rats was comparatively studied. The dependence of DMF upon oxygen concentration in the mixture was approximated by a hyperbolic function similar to the dependence of the radiomodifying effect of circulatory hypoxia caused by radioprotective agents of the indolylalkylamine series.     

Mechanism of circulatory disorders in animals irradiated at high doses

Some data are reported on pathoanatomical changes, a status of the microcirculatory channel and the coagulogram of animals affected by high doses of ionizing radiation. The signs of disseminated intravascular blood coagulation have been revealed. The authors discuss the relationship between clinical manifestations with coagulopathy development and circulatory disturbances during intestinal and cerebral forms of acute radiation sickness.     

Study of the kinetics of thermoinactivation of lysyl-tRNA-synthetase from the liver of x-irradiated rats

A study was made of the kinetics of thermoinactivation of lysyl-tRNA-synthetase isolated from rat liver at early times of radiation damage development after the effect of a minimum absolutely lethal X-radiation dose (0.21 C/kg). The thermostability of a dimer form of the enzyme was shown to be higher than that of a monomer. It was established that substrates had a stabilizing effect on the enzyme during thermoinactivation. On the basis of the data obtained from the studies in the kinetic properties of the enzyme and the thermoinactivation a conclusion is made that lysyl-tRNA-synthetase is stabilized during subunit aggregation. The thermostability of the enzyme was decreased by irradiation.     

Localized mutagenesis of the tetracycline gene in the plasmid pBR322 induced by sodium bisulfite in vitro

The technique of localized in vitro mutagenesis in the cohesive ends of plasmid pBR322 DNA has been elaborated (separately for BamHI and HindIII sites). Plasmid DNA digested by restriction endonucleases has been treated with sodium bisulphite deaminating cytosine to form uracil in single stranded DNA (cohesive ends of the plasmid). The mutagenized plasmid DNA, free of mutagen, has been treated with bacteriophage T4 ligase. E. coli C600 cells were subsequently transformed by the ligated DNA preparation. The clones having tetracycline gene mutagenized represented 4.0-11.1% and 1.2-3.1% among HindIII and BamHI mutants, respectively, selected as TcR----TcS transformants. Selection of mutagenized DNA by the second endonuclease restriction has increased the mutant yields up to 55.6-78.0% and 10.0-75.4%, respectively. The yield of TcS mutations in the control DNA treated at all stages of experiment, except for mutagen treatment, has reached 0.06% and 0.2%, respectively.     

Properties of cathepsin D from unfertilized eggs, embryos and skeletal muscles of the loach

The action and some properties of cathepsin D, partly purified from unfertilized loach eggs, embryos and skeletal muscles were determined. The enzyme from embryo cells displays the activity maximum at pH 3.0 and pH 4.8 while enzyme from skeletal muscles--only at pH 3.0. Cathepsin D purified from all three sources splits actively hemoglobin, albumin, alpha-glycerophosphate dehydrogenase, pyruvate kinase and practically does not influence casein, hexokinase, glucose-6-phosphate dehydrogenase. The enzyme is comparatively thermolabile and its activity decreases in the presence of thiol compounds. The main part of cathepsin D in skeletal muscle cells and in embryo cells is precipitated after differential centrifugation of homogenates (25000 g; 60 min).     

Specific vacuolation of frog urinary bladder granular cell after ADH stimulation of water transport

The present study deals with an analysis of specific traits of cell vacuolation induced by water flow and ADH. During incubation of frog urinary bladders in Ringer's solution diluted 2-fold, the water content of the bladder wall increased by an average of 19%. In case of ADH-stimulated water flow the water content increased by an average of 15.7%. Cell swelling induced by hypotonic conditions on the serosal side resulted in a drastic decrease of the response to the hydroosmotic action of ADH. Electron microscopy revealed significant differences between cells hydrated in the above conditions. Two-fold hypotonicity of the serosal solution caused a slight swelling of all types of cells accompanied by a narrowing of intercellular spaces. With ADH stimulation of water transport (at maximal water movement) granular cells were characterized by the presence of irregularly shaped giant vacuoles with processes. The limiting membranes of the vacuoles were closely connected with microtubules and microfilaments. The electron microscopic study of these cells by the freeze-substitution method revealed, in addition to giant vacuoles, a highly complex system of microtubules 35-40 nm in diameter. A morphological similarity was observed between the vacuolar systems of these granular cells and the contractile vacuole complex of protozoans. Possible mechanisms for the participation of giant vacuoles, electron-dense canaliculi, microtubules and microfilaments in transcellular water flow across epithelium are discussed.     

Ionic currents in nerve terminals of the frog sartorius muscle

Nerve terminal responses produced by stimulating the motor nerve were recorded extracellularly from the nerve endings of the frog sartorius muscle. A triphasic response occurred in the proximal areas of the nerve ending, beginning with a positive phase. Ionotophoretic application of tetrodotoxin, tetraethylammonium, and 4-aminopyridine indicated that the negative phase reflected inward sodium current and the third (positive) phase indicated outward potassium current. A late slow negative component was recorded using CaCl₂-filled electrodes during perfusion of erve-muscle preparations with a calcium-free solution containing tubocurarine. This component was dependent on the Ca²⁺ concentration present in the electrode, increasing when tetraethylammonium and 4-aminopyridine were added and disappearing under the effects of Co²⁺. Similar components were recorded using microelectrodes containing Sr²⁺ and Ba²⁺. It was deduced that the slow components in the response indicate currents passing through voltage-dependent calcium channels in the presynaptic membrane of the nerve ending. The time course of the calcium current is compared with that of transmitter release at the synapse.S. V. Kurashov Medical Institute, Ministry of Health of the RSFSR, Kazan'. V. I. Ulanov-Lenin Kazan' State University. Translated from Neirofiziologiya, Vol. 17, No. 6, pp. 770–779, November–December, 1985.