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Biomedical subjects

R G Johnson

Publications and source records attributed to R G Johnson.

At least 217 records · Page 12Linked to original sources
PubMed1979

Protonmotive force and catecholamine transport in isolated chromaffin granules.

The effect of the transmembrane potential (delta psi) and the proton concentration gradient (delta pH) across the chromaffin granule membrane upon the rate and extent of catecholamine accumulation was studied in isolated bovine chromaffin granules. Freshly isolated chromaffin granules had an intragranular pH of 5.5 as measured by [14C]methylamine distribution. The addition of ATP to a suspension of granules resulted in the generation of a membrane potential, positive inside, as measured by [14C]thiocyanate (SCN-) distribution. The addition of carboxyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), a proton translocator, resulted in a reversal of the potential to negative values (measured by [3H]tetramethylphenylphosphonium (TPMP+)) approaching -90 mV. Changing the external pH of a granular suspension incubated with FCCP produced a linear perturbation in the measured potential from positive to negative values, which can be explained by the distribution of protons according to their electrochemical gradient. When ammonia (1 to 50 mM) was added to highly buffered suspensions of chromaffin granules there was a dose-dependent decrease in the transmembrane proton gradient (delta pH) and an increase in the membrane potential (delta psi). On the other hand, thiocyanate or FCCP, at varying concentration, produced a dose-related collapse of the membrane potential and had no effect upon the transmembrane proton gradient. The addition of larger concentrations of catecholamines caused a decrease in the transmembrane proton gradient and an increase in the membrane potential. Time-resolved influx of catecholamines into the granules was studied radiochemically using low external catecholamine concentrations. The accumulation of epinephrine or norepinephrine was over one order of magnitude greater in the presence of ATP than in its absence. The rate and extent of amine accumulation was found to be related to the magnitude of the membrane potential at fixed transmembrane proton concentration (delta pH) values. Likewise, the accumulation was related to the magnitude of the delta pH at fixed membrane potential values. These results suggest that the existence of both a transmembrane proton gradient and a membrane potential are required for optimal catecholamine accumulation to occur.

Adrenal Glands↗
PubMed1979

Tight junction development between cultured hepatoma cells: possible stages in assembly and enhancement with dexamethasone.

Freeze-fracture and thin-section methods were used to study tight junction formation between confluent H4-II-E hepatoma cells that were plated in monolayer culture in media with and without dexamethasone, a synthetic glucocorticoid. Three presumptive stages in the genesis of tight junctions were suggested by these studies: 1) "formation zones" (smooth P-fracture face ridges deficient in intramembranous particles), apparently matched across a partially reduced extracellular space, develop between adjacent cells; 2) linear strands and aggregates of 9--11 nm particles collect along the ridges of the formation zones. The extracellular space was always reduced when these structures were found matched with pits in gentle E-face depressions; 3) the linear arrays of particles on the ridges associate within the membranes to form the fibrils characteristic of mature tight junctions. The formation zones resemble tight junctions in terms of size, complexity and the patterns of membrane ridges. Although some of the beaded particle specializations may actually be gap junctions, it is unlikely that all can be interpreted in this way. No other membrane structures were detected that could represent developmental stages of tight junctions. Dexamethasone (at 2 x 10(-6)M) apparently stimulated formation of tight junctions. Treated cultures had a greater number of formation zones and mature tight junctions, although no differences in qualitative features of the junctions were noted.

Animals↗
PubMed1979

Uptake of [14C]choline and incorporation into lung phospholipid by the isolated perfused rat lung.

We have used the isolated perfused lung (IPL) preparation from the rat to determine whether uptake of choline from the vascular compartment could limit the rate of synthesis of phosphatidyl-choline (PC). The uptake of choline was rapid and did not saturate at a concentration of 10 mM. The rate of incorporation of choline into phospholipid was saturated above 0.1 mM choline. Whereas, uptake and incorporation were depressed at 4 C, uptake was neither dependent on the extracellular sodium concentration nor inhibited by equimolar concentrations of hemicholinium-3 (HC-3). We could find no evidence that uptake might limit synthesis of lung lecithin and conclude that uptake is either by free diffusion, or by a carrier-mediated process with a very high Km.

Animals↗
PubMed1979

The restraint of rabbits in a special sling.

A special sling for the restraint of rabbits was developed for the investigation of the effects of continuous motion on the healing of intraarticular injuries. Studies of over 200 rabbits have demonstrated the sling restraint system to be effective and humane, with a restraint related mortality of less than 10%.

Animals↗
PubMed1978

The internal pH of isolated serotonin containing granules of pig platelets.

The [14C]methylamine distribution method was utilized to measure the internal pH of isolated serotonin containing granules of pig blood platelets under varying conditions. The granules used were isolated by a new protocol which stressed platelet rupture under controlled conditions and preservation of isotonicity throughout the isolation procedure, In a well buffered external medium, pH 6.85, The deltapH was measured as 1.11 with the internal pH being found acidic (pH 5.74). Increasing the external pH produced a corresponding increase in the deltaH. The pH gradient could be collapsed by the addition of ionophores and uncouplers which are known to transport protons across biological membranes. In addition, the deltapH was constant for granules suspended in various ionic media, thus suggesting that the deltaH did not arise secondarily due to the establishment of a Donnan equilibrium. The existence of the acidic intragranular space is discussed with respect to previous ancillary findings. Also, an explication of the possible physiological significance of the deltaH is presented.

Animals↗
PubMed1978

Quantitative analysis of low-resistance junctions between cultured cells and correlation with gap-junctional areas.

Electrophysiological studies of low-resistance junctions between Novikoff hepatoma cells grown in suspension cultures were carried out and correlated with gap-junctional areas per inferface determined by freeze-fracture. The mean coupling coefficient between isolated cell pairs was 0.773 +/- 0.025 (SEM) in 67G medium and 0.653 +/- 0.028 in M67 medium; the respective means for the central pairs of four-cell chains were 0.714 +/- 0.034 and 0.595 +/- 0.026. Mean estimates of nonjunctional resistances for cell pairs were 3.0 +/- 0.32 x 10(7) ohm (67G) and 2.01 +/- 0.01 x 10(7) ohm (M67), and the respective estimates for specific nonjunctional resistances were 158.6 +/- 8.1 ohm-cm2 (67G) and 133.0 +/- 812 ohm-cm2 (M67). Mean estimates of junctional conductances were 0.409 +/- 0.058 x 10(-6) mho (67G) and 0.211 +/- 0.018 x 10(-6) mho (M67) for pairs and 0.291 +/- 0.063 x 10(-6) mho (67G) and 0.212 +/- 0.04 mho (M67) for four-cell chains. The mean area of gap junction per interface for separate cell populations was 0.187 +/- 0.049 micron 2 and 0.269 +/- 0.054 micron 2 for cells fixed in loose pellets and in suspension, respectively. When compared with the mean junctional conductance, these values gave specific junctional conductance estimates of 1.13 x 10(2) mho/cm2 and 0.78 x 10(2) mho/cm2, respectively. These values are higher than most previous estimates, but are consistent with the hypothesis that gap-junctional particles contain central hydrophilic channels, about 2 nm in diameter, which have cytoplasmic resistivity.

Animals↗
PubMed1977

Linearity of exposure with indicated time and current for diagnostic radiography units.

Quality control in diagnostic radiography begins with production of predictable exposures. The authors describe a technique which permits determination of the variation of mR/mAs for the entire diagnostic range of times and currents in only about 1 hour. The mR/mAs in newly installed units has been shown to vary by as much as +/- 50% compared to institutional acceptance levels of +/- 10%. Records of annual surveys and acceptance tests from 31 medical facilities, including 293 radiographic and fluoroscopic units, are reviewed, and effects of small variations in mAs on radiographic quality are shown.

Humans↗
PubMed1976

Internal pH of isolated chromaffin vesicles.

The passive permeability of isolated chromaffin vesicles to H+ and the internal pH of the vesicles under various conditions were measured. Potentiometric measurements of K+ and H+ fluxes in the presence of selected ionophores and uncouplers indicated that the membrane is highly impermeable to both protons and potassium. deltapH across the chromaffin granule membrane was measured by [14C]methylamine distribution. At pH 6.85, The deltapH WAS 1.16 WITH THE INTRAVESICULAR SPACE BEING FOUND ACIDIC. Varying the external pH produced an equivalent change in the deltapH, WITH EXTRAPOLATION TO ZERO DEltapH yielding a value of pH 5.5, WHICH IS TAKEN AS AN INDICATION OF THE PH of the intravesicular space. The pH gradient could be enhanced or collapsed by the addition of ionophores and uncouplers under varying ionic conditions. deltapH was constant for granules suspended in various ionic media, suggesting that the deltapH did not arise secondarily due to the establishment of a Donnan equilibrium. The significance of the proton impermeability and deltapH is discussed in terms of regulation of the uptake and storage of catecholamines in bovine chromaffin granules.

Adrenal Medulla↗
PubMed1976

Cytoplasmic inheritance in Saccharomyces cerevisiae: comparison of zygotic mitochondrial inheritance patterns.

Mitochondrial movements in Saccharomyces cerevisiae (Sc) zygotes were monitored with phase-contrast microscopy and compared to known mitochondrial inheritance systems. The mitochondria of Sc were convincingly identified by integrated use of phase-contrast, cytochemical and electron microscopic observations. Mitochondria in Sc appear to move by saltatory jumps, which appear to be oriented towards movement of mitochondria into developing buds. Tracking of mitochondria of different genotypes was made possible by positive identification of each mitochondrial population before zygosis, and by the low degree of mixing (less than 10%) of mitochondrial populations before first bud septation. A grande by grande cross demonstrated equal numbers of mitochondria from each haploid moving into the first zygotic bud. A grande by neutral petite cross gave a 2:1 ratio of grande to petite mitochondria. However, a grande by suppressive petite cross gave equal numbers of grande and petite mitochondria. Using drug resistance systems, a comparison was made of highly biased (97%) and moderately biased (71%) chloramphenicol resistant inheritance patterns. In both cases, the ratios of drug resistant to sensitive mitochondria were 1:1. When numbers of mitochondria moving into an individual bud were compared to the phenotypic content of the clone of that bud, no model could be constructed which could predict the latter from the former. The data indicate (with the exception of the neutral petite by grande cross) that the numbers of each mitochondrial type "inserted" into the first zygotic bud are equal, regardless of the degree of asymmetry of inheritance of mitochondrial markers.

Chloramphenicol↗
PubMed1976

Ion permeability of isolated chromaffin granules.

The passive ion permeability, regulation of volume, and internal pH of isolated bovine chromaffin granules were studied by radiochemical, potentiometric, gravimetric, and spectrophotometric techniques. Chromaffin granules behave as perfect osmometers between 340 and 1,000 mosM in choline chloride, NaCl, and KCl as measured by changes in absorbance at 430 nm or from intragranular water measurements using 3H2O and [14C]polydextran. By suspending chromaffin granules in iso-osmotic media of various metal ions and selectively increasing the permeability to either the cation or the anion by intrinsically permeable ions or specific ionophores, it was possible to determine by turbidity and potentiometric measurements the permeability to the counterion. These measurements indicate that the chromaffin granule is impermeable to the cations tested (Na+, K+, and H+). Limited H+ permeability across the chromaffin granule membrane was also shown by means of the time course of pH re-equilibration after pulsed pH changes in the surrounding media. The measurement of [14C]methylamine distribution indicates that a significant deltapH exists across the membrane, inside acidic, which at an external value of 6.85 has a value of 1.16. The deltapH is relatively insensitive to changes in the composition of the external media and can be enhanced or collapsed by the addition of ionophores and uncouplers. Measurement at various values of external pH indicates an internal pH of 5.5. Use of the ionophore A23187 indicates that Ca++ and Mg++ can be accumulated against an apparent concentration gradient with calcium uptake exceeding 50 nmol/mg of protein at saturation. These measurements also show that Ca++ and Mg++ are impermeable. Measurement of catecholamine release under conditions where intravesicular calcium accumulation is maximal indicates that catecholamine release does not occur. The physiological significance of the high impermeability to ions and the existence of a large deltapH are discussed in terms of regulation of uptake, storage, and release of catecholamines in chromaffin granules.

Adrenal Medulla↗
PubMed1975

Postirradiation atrophic changes of bone and related complications.

The sequence of radiographically visible changes about the shoulder girdle following irradiation was analyzed in 49 patients who received 200 kV irradiation, in 50 who received 25 MeV betatron photon irradiation, and in 20 who received cobalt-60 irradiation. The changes were dose related and were most evident in the kilovoltage group, but also occurred following megavoltage therapy. Atrophic changes may be complicated by fracture, true necrosis, true osteitis or sarcoma. These atrophic changes have clinical significance similar to the atrophic changes that occur in skin and mucous membranes. The terms radionecrosis and radiation osteitis as applied to these changes should be abandoned since they imply a more serious process than is actually present. Biopsy should be avoided if possible since trauma and secondary infection could lead to true necrosis.

Atrophy↗