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Biomedical subjects

R A Murphy

Publications and source records attributed to R A Murphy.

At least 181 records · Page 10Linked to original sources
PubMed1977

Synthesis and secretion of a high molecular weight form of nerve growth factor by skeletal muscle cells in culture.

Rat skeletal muscle cells and a cloned myogenic cell line synthesize and secrete in culture a molecule that is immunologically and biologically indistinguishable from the active form of nerve growth factor (NGF) from mouse submandibular gland. This protein can be detected in medium conditioned by muscle cells both before and after fusion and in the soluble fraction of muscle cell homogenates. Chromatographic data also reveal that the molecular properties of muscle cell NGF differ from those of the growth factor purified from mouse submandibular glands. Muscle cell NGF has a molecular weight between 140,000 and 160,000, whereas purified mouse gland NGF has a molecular weight of 26,000. The biologic function of muscle cell NGF is not known, although it could be that it plays some role relating to the association of nerves and muscle in vivo.

Animals↗
PubMed1977

Nerve growth factor in mouse serum and saliva: role of the submandibular gland.

The concept that the salivary gland of the mouse is an endocrine organ for nerve growth factor (NGF) has been reexamined. Serum concentrations of the protein have been measured by radioimmunoassay in male and female mice and in mice from which the submandibular glands were removed. In spite of the fact that the submandibular glands of male mice contained more NGF than did those of female mice, no sex differences in circulating concentrations of the factor were detected. Furthermore, serum concentrations of NGF did not change after submandibular gland removal or after administration of several autonomic agonists. These results indicate that the submandibular glands are not endocrine organs with respect to NGF. On the other hand, extremely high concentrations of the factor are normally secreted in mouse saliva at levels that reflect the sex differences in the amount of NGF present in the glands. This finding suggests that the salivary gland is an exocrine organ for NGF and that the protein may play a biological role in saliva.

Animals↗
PubMed1977

Molecular properties of the nerve growth factor secreted in mouse saliva.

Some molecular properties of the nerve growth factor (NGF) secreted in mouse saliva and that present in submandibular glands have been measured for comparison with previously studied forms of NGF. The results show that mouse saliva contains two biologically active NGF species. One has a molecular weight near 114,000, and the other, a molecular weight of 13,000. The larger form is being continuously degraded to yield the smaller one, probably as a result of a slow enzymatic process. Virtually identical results were obtained with crude submandibular gland extracts. The larger NGF is neither the well-known 7S NGF nor 2.5S NGF. Our results indicate that the larger salivary NGF is the naturally occurring form of NGF as it exists in the submandibular gland and as it is secreted in saliva. Its biological properties and its function in saliva, if any, remain to be elucidated.

Animals↗
PubMed1977

Production and detection of staphylococcal elastase.

The optimum conditions were determined for the production and detection of staphylococcal elastase from Staphylococcus epidermidis. Optimum production and recovery took place when the dialysis membrane technique was utilized with brain heart infusion agar incubated for 44 h under 15% CO2 and harvested in physiological saline. Near-optimal production took place by 28 h, and this was found more useful for routine use. Incorporation of elastin into the culture medium or the inoculum did not result in higher levels of elastase production. The detection system consisted of 0.25% particulate elastin suspended in a pH 7.0, 0.05 M tris(hydroxymethyl)aminomethane-hydrochloride-buffered solidified plated medium. Crude undialyzed elastase was best detected when the medium contained either agarose and 10(-3) M calcium or purified agar without additional additives. Crude dialyzed elastase was best detected when the medium contained agarose and 10(-3) M disodium ethylenediaminetetraacetic acid.

Aerobiosis↗
PubMed1976

Structural proteins in the myofilaments and regulation of contraction in vertebrate smooth muscle.

The contractile systems of vertebrate smooth and striated muscles are compared. Smooth muscles contain relatively large amounts of actin and tropomyosin organized into thin filaments, and smaller amounts of myosin in the form of thick filaments. The protein contents are consistent with observed thin:thick filament ratios of about 15-18:1 in smooth compared to 2:1 in striated muscle. The basic characteristics of both types of contractile proteins are similar; but there are a variety of quantitative differences in protein structures, enzymatic activities and filament stabilities. Biochemical and X-ray diffraction data generally support recent ultrastructural evidence concerning the organization of the myofilaments in smooth muscle, although a basic contractile unit comparable to the sarcomere in striated muscle has not been discerned. Myofilament interactions and contraction in smooth muscle are controlled by changes in the Ca2+ concentration. Recent evidence suggests the Ca2+-binding regulatory site is associated with the myosin in vertebrate smooth muscle (as in a variety of invertebrate muscles), rather than with troponin which is the regulatory protein associated with the thin filament in vertebrate striated muscle.

Actomyosin↗
PubMed1976

Molecular size of nerve growth factor in dilute solution.

Nerve growth factor (NGF) is a protein composed of two identical chains of mass 13,259. An analysis of the sedimentation equilibrium, sedimentation velocity, and gel filtration behavior of dilute solutions of NGF indicates the existence of a rapidly reversible monomer in equilibrium dimer equilibrium and that the association constant K for the reaction at neutral pH is 9.4 X 10(6)M-1. Reaction mixtures consist of equal concentrations of monomer and dimer at a total protein concentration as high as 1.4 mug/ml, and at 1 ng/ml, monomer accounts for greater than 99% of the total. The latter concentration is 20 to 30 times that required for the biological activity of NGF. Several lines of evidence suggest that the dimerization reaction is highly stereospecific, although its biological significance is not known.

Animals↗
PubMed1976

Contractile system function in mammalian smooth muscle.

The literature on the classical mechanical properties of geometrically simple mammaliam smooth muscle preparations is analyzed in an attempt to characterize the contractile system. Although the physiological behavior of smooth muscle is diverse, indices of contractile system function suggest there is considerable uniformity at this level. Compared to vertebrate striated muscles, smooth muscle tissues and possibly individual cells (i) often develop equal or greater maximum isometric force/cell cross-sectional area, with (ii) low and fairly uniform maximum shortening velocities, and (iii) operate over a range of lengths which may be no greater than the potential in striated muscle. Few details are known of filament structure, organization, interactions, and of force transmission in comparison with the extensive information on the contractile unit (sarcomere) for striated muscle. Consequently, tissue or cellular mechanical parameters may not be directly proportional to the output of the myofilamental contractile unit smooth muscle. A sliding filament mechanism involving actin-myosin interactions qualitatively similar to those in striated muscle seems probable. However, there are important quantitative differences in the contractile, apparatus which may be related to functional properties.

Animals↗
PubMed1976

Stress relaxation in hog carotid artery as related to contractile activity.

The purpose of this work was to test the hypothesis that stress relaxation (SR) in vascular smooth muscle is related to the amount of contractile activity (developed stress) and perhaps a property of the contractile element (CE). Using medial-intimal strips from the hog carotid artery, a strain (delta 1/l0, where l0 equals optimal length for force development) of 2% was applied at two different rates in the presence of various levels of developed or passive stress. Developed stress was altered either by changing the extracellular K-ion concentration with the strip length equal to l0 or by stimulating with a salt solution containing 30 mM KCl at various strip lengths. Passive stress was altered by varying strip length. At each level of developed or passive stress the magnitude of the increment in stress due to the strain (induced stress) and the SR were noted. SR varied directly with the magnitude of the developed stress, but there was a small and relatively unchanging amount of SR when passive stress was varied. At a given level of developed stress, the magnitude of SR was greater at a strain rate of 0.016 than at 0.001 l0/sec. When developed stress was altered, the magnitude of SR was essentially equal to the amount of induced stress; however, when passive stress was varied, SR was always less than induced stress. These observations are consistent with the hypothesis that, in the presence of developed stress, a large fraction of the SR represents the lengthening of the CE. This increased CE length allows a reequilibration of stress between the series elastic element and the contractile element. In the absence of developed stress, SR may represent a passive, physical property of this heterogeneous tissue.

Animals↗
PubMed1975

Myosin from arterial smooth muscle: isolation following actin depolymerization.

The contractile proteins from arterial smooth muscle are highly soluble, and can be extracted at I = 0.05. However, they can be precipitated by a prolonged dialysis at pH 6 to give an actomyosin with a high, although variable, actin:myosin ratio. The sedimentation behavior of this actomyosin at high ionic strength was examined as a function of pH, protein concentration and composition by preparative ultracentrifugation. Comparisons with synthetic skeletal muscle actomyosins of similar composition demonstrated significant differences in the behaviors of these two systems. It was found that much smooth muscle actomyosin is not dissociated by normally relaxing conditions, and that it sediments at a slower rate than F-actin. The solubility of the supernatant protein (a myosin-enriched actomyosin) in 0.2 M K Cl (pH 7) depended on the pH during centrifugation. A lower solubility was associated only with a higher actin concentration in the supernatant, suggesting a dependence on actin repolymerization. Pure myosin was selectively precipitated from the supernatant by polyethylene glycol-6000, but only when the protein was soluble at low ionic strength. The solubility of purified myosin was similar to that of myosin from striated muscles. A relationship between the presence of depolymerized actin and the high solubility of smooth muscle contractile proteins is suggested.

Actins↗
PubMed1975

Secretion of a nerve growth factor by mouse neuroblastoma cells in culture.

Analyses of supernatant solutions from mouse C1300 neuroblastoma cultures by two independent immunoassays reveal that these cells secrete a factor which is immunochemically similar to mouse submaxillary gland nerve growth factor. The neuroblastoma factor is also biologically active in inducing neurite outgrowth from embryonic sensory ganglia-an effect that is completely blocked by specific antibody to nerve growth factor. Neuroblastoma cells are known to be functionally responsive to nerve growth factor, and the observation that they secrete a molecule like it may mean that these cells require or utilize the factor during growth in culture.

Animals↗
PubMed1974

Force-generating capacity and contractile protein content of arterial smooth muscle.

After correction for extracellular space (40%) determined from electron micrographs, the maximum isometric force developed by strips prepared from the media of the hog carotid artery (2.2 x 10(6) dyn/cm(2)) can be extrapolated to give a value of 3.7 x 10(6) dyn/cm(2) for the smooth muscle component of the strip. Three independent estimates of the myosin content of the smooth muscle cells were made based on (a) exhaustive extraction and purification with estimates of preparative losses, (b) the myosin catalyzed ATPase activity of media homogenates, and (c) quantitative densitometry of the peaks containing myosin, actin, and tropomyosin after disk electrophoresis of sodium dodecyl sulfate-treated media homogenates. The results were consistent and gave a myosin content of 5-10 mg/g media, or 8-17 mg/g cell. Method (c) gave myosin:actin:tropomyosin weight ratios of 1:3.2:0.8. Although measured force developed by the smooth muscle cell exceeds that of mammalian striated muscle, the myosin content in smooth muscle is about five times lower. The actin content of smooth muscle is relatively high. The actin and myosin contents are consistent with thick and thin filament ratios observed in electron micrographs of vascular smooth muscle.

Actins↗