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Biomedical subjects

R G Johnson

Publications and source records attributed to R G Johnson.

At least 199 records · Page 11Linked to original sources
PubMed1982

Comparison of myocardial preservation with hypothermic potassium and nifedipine arrest.

Preservation of regional myocardial function, high-energy phosphate stores and ultrastructure were assessed in 28 canine hearts subjected to 2 hours of global ischemia at either 12 degrees C or 21 degrees C. The preservation achieved with a potassium arrest solution was simultaneously compared in the same heart with either a nifedipine arrest solution or a potassium plus nifedipine arrest solution. There were no statistically significant differences in regional function recovery between the three arrest solutions at either temperature. At 12 degrees C, slightly better functional preservation was noted for each solution. End-systolic chord length was significantly less elongated after preservation at the lower temperature (p = 0.03). The concentration of ATP and myocardial water content were not significantly better preserved with any solution at either temperature. Myocardial ultrastructure was well preserved regardless of the solution or temperature used. The degree of hypothermia appears to be more important to functional preservation than differences between the three solutions tested. We conclude that with respect to preservation of myocardial function, high-energy phosphate stores, water content and ultrastructure, nifedipine arrest offers no advantages over potassium arrest.

Adenosine Triphosphate↗
PubMed1982

A model of biogenic amine accumulation into chromaffin granules and ghosts based on coupling to the electrochemical proton gradient.

A model is presented to explain catecholamine uptake into isolated chromaffin granules and ghosts. It is based on the following observations and conclusions: 1) the chromaffin granule maintains one of the lowest permeabilities to cations of any previously isolated subcellular organelle and the lowest permeability to protons, 2) a transmembrane proton gradient delta pH exists across the chromaffin granule membrane that is not media dependent, with a measured internal pH of 5.5; 3) the addition of ATP to a suspension of chromaffin granules results in the generation of a membrane potential of 80-100 mV, positive inside; 4) an H+-translocating ATPase responsible for the generation of this electrochemical proton gradient (delta micro H+) exists within the membrane of the chromaffin granule; 5) net amine accumulation proceeds in the presence of both a delta pH alone and a transmembrane potential gradient delta psi alone, with the maximal rate and extent occurring in the presence of a delta pH and a delta psi together (delta micro H+); 6) when catecholamine uptake is in equilibrium with the delta micro H+, the equilibrium distribution of amines (delta micro A) obeys the relationship delta micro A = delta psi-2Zdelta pH. The model, in its elemental form, states that an H+-translocating ATPase for the generation of a delta pH and delta psi exists within the membrane of the chromaffin granule. This electrochemical proton gradient provides the driving force for amine influx, which proceeds via a reserpine-sensitive antiport carrier mechanism coupled to proton efflux. The model is discussed in terms of its physiological implications and significance for other amine-containing subcellular organelles, with particular respect to the species of catecholamine transported, and other unresolved issues.

Animals↗
PubMed1981

The electron transport chain of serotonin-dense granules of platelets.

An electron transport chain has been found and partially characterized in highly purified membranes of serotonin granules isolated from porcine platelets. In these membranes NADH, but not NADPH, is oxidized when ferricyanide or catalytic amounts of cytochrome c were present. The reduced minus oxidized spectrum of these serotonin granule membranes shows a characteristic cytochrome b spectrum with absorbance maxima at 428, 530, and 561 nm. Ascorbate and, at slower rates, NADH are electron donors to cytochrome b561. It is concluded that the electron transport chain present within the membranes of serotonin granules is virtually identical with that of chromaffin granules, and a common physiological role is suggested.

Animals↗
PubMed1981

Serotonin transport in isolated platelet granules. Coupling to the electrochemical proton gradient.

The effect of the transmembrane proton gradient (delta pH) and potential gradient (delta psi) upon the rate and extent of amine accumulation was investigated in intact 5-hydroxytryptamine (serotonin) containing dense granules. The granules were isolated and purified from other subcellular organelles under isotonic conditions utilizing a newly developed continuous density gradient of Percoll. As measured by [14C]methylamine distribution, isolated granules suspended in a highly buffered medium at pH 7.0 had an intragranular pH of 5.40, independent of the pH of the external medium. This pH gradient could be collapsed by the addition of 60 mM ammonia. In the presence of Mg-ATP, a transmembrane potential (delta psi) of 30-40 mV, inside positive, was generated and sustained for over 30 min, as measured by [14C]thiocyanate distribution. The addition of carbonyl cyanide p-trifluoromethoxyphenylhydrazone, a proton translocator, resulted in the reversal of the potential to negative values. The Mg-ATP-dependent generation of the delta psi was prevented by addition of dicyclohexylcarbodiimide and trimethyltin, inhibitors of proton-translocating ATPases in this and other subcellular organelles. Ammonia (1-50 mM) addition to highly buffered suspensions of serotonin granules caused a dose-dependent decrease in the delta pH, while thiocyanate added at varying concentrations produced a dose-related collapse of the delta psi and had no effect upon the delta pH. Both the delta pH and delta psi were found to independently drive accumulation of [14C]serotonin into the granules; stepwise collapse of each gradient resulted in a corresponding diminution of [14C]serotonin accumulation. The maximum rate and extent of [14C]serotonin uptake, however, were observed in the presence of both the delta pH and delta psi. The conclusions provide support for the existence of a proton-translocating ATPase in the serotonin granule membrane responsible for the generation of the delta pH and delta psi. Moreover, the results demonstrate a primary role for the electrochemical proton gradient (delta mu H+) in the carrier-mediated active transport of 5-hydroxytryptamine into the platelet granule.

Adenosine Triphosphatases↗
PubMed1981

Proton: substrate stoichiometries during active transport of biogenic amines in chromaffin ghosts.

The relationship between the electrochemical proton gradient (delta mu-H+) and the electrochemical gradient for biogenic amines (delta mu-A) was investigated in isolated chromaffin ghosts free of endogenous components and gradients. The addition of ATP to a ghost suspension resulted in the generation of a large proton concentration gradient (delta pH), acidic inside (measured by [14C]-methylamine distribution), and a large proton electrical gradient (delta psi), positive inside (measured by [14C]-thiocyanate distribution). In the presence of this large electrochemical proton gradient, the accumulation of [14C]5-hydroxytryptamine (serotonin) and other biogenic amines rapidly reached an apparent steady state level. Collapse of the proton gradients after steady state levels were achieved resulted in the efflux of the accumulated amines. Uptake in the presence of a delta psi alone produced an amine gradient equal to the magnitude of the delta psi, while in the presence of a delta pH alone biogenic amine distribution was equal to twice the magnitude of the delta pH. Using additions of ammonia or thiocyanate, it was possible to vary the magnitude of the electrochemical proton gradient over a wide range of values; the driving force for amine accumulation under these conditions was found to be equal to delta psi--2Z delta pH (where Z = 2.3 RT/F). The results, which provide unequivocal evidence for the primary role of the electrochemical proton gradient in the active transport of biogenic amines, are consistent with a model based on the chemiosmotic hypothesis, of an obligatory coupling of amine influx and proton efflux, mediated via a putative reserpine-sensitive translocator. Measurement of the stoichiometry of this coupling of H+ and amines permits conclusions concerning the molecular mechanism of amino accumulation.

Ammonia↗
PubMed1981

Rapid and reversible reduction of junctional permeability in cells infected with a temperature-sensitive mutant of avian sarcoma virus.

The transformed or normal phenotype of cultured normal rat kidney cells infected with a temperature-sensitive mutant of avian sarcoma virus is conditional on the temperature at which the cells are grown. Using dye injection techniques, we show that junction-mediated dye transfer is also temperature-sensitive. The extent and rate of transfer between infected cells grown at the transformation-permissive temperature (35 degrees C) is significantly reduced when compared to infected cells grown at the nonpermissive temperature (40.5 degrees C) or uninfected cells grown at either temperature. Infected cells subjected to reciprocal temperature shifts express rapid and reversible alterations of dye transfer capacities, with responses evident by 15 min and completed by 60 min for temperature shifts in either direction. These results suggest that altered junctional capacities may be fundamental to the expression of the ASV-induced, transformed phenotype.

Alpharetrovirus↗
PubMed1981

Myocardial temperature mapping. Improved intraoperative myocardial preservation.

An improved approach to intraoperative myocardial preservation technique to ensure uniform myocardial cooling past critically stenosed arteries was developed for patients undergoing aorta-coronary bypass grafting. Proximal anastomoses are done and then, after institution of cardiopulmonary bypass, a separate roller pump head is used to administer a specific controlled volume of cardioplegic solution (1 L) through a 4 degrees C coil to provide controlled pressure in the root of the cross-clamped aorta. Midmyocardial wall temperatures in the anterior, posterolateral, inferior, and septal walls of the left ventricle are measured. Distal anastomoses are then performed sequentially, beginning with the warmest region. After each distal anastomosis, 400 ml of cardioplegic solution are again administered into the aortic root. This approach has been used in 100 consecutive patients from July, 1979, through July 1980 (Group I). and these patients were compared to 97 consecutive patients undergoing aorta-coronary bypass grafting in the previous year (July, 1978, through June, 1979) (Group II) who had myocardial preservation with potassium cardioplegia administered by syringe injection and without regional temperature mapping. There were no perioperative myocardial infarctions in Group I: there were five (5.2%) in Group II (p less than 0.05). A significant reduction in cardiac deaths was also achieved, with two (2.0%) such deaths in Group I and eight (8.2%) in Group II (p less than 0.05). The data suggest that delivery of adequate volumes of cardioplegia solutions by a pressure-regulated system, in combination with myocardial temperature mapping to determine the sequence of bypass grafting, can improve myocardial preservation.

Body Temperature↗
PubMed1981

Phospholipid synthesis in isolated perfused lungs of rats made tolerant to 100% oxygen.

Tolerance to 100% oxygen is readily induced in the rat by prior exposure to 80% oxygen for 7 days. In order to determine whether the rate of synthesis, or te alveolar content, of pulmonary phospholipids is altered in the tolerant rat, we perfused the isolated lung with medium containing 20 muM [14C]methyl choline chloride for 30 min at 10 ml/min, and then we measured the incorporation of carbon-14 into tissue phospholipids. We also measured the phospholipids in the lavage. There was no difference in the rate of incorporation in the tolerant rats (201 +/- 11 nmol/g dry lung, n = 8, mean +/- SEM) compared to control rats (210 +/- 9 nmol/g dry lung, n = 4) that had been exposed to air for 7 days under identical conditions. Whereas the induction of tolerance did not alter the total amount of phospholipid lavaged from the lung (tolerant: 251 +/- 31 microgram lipid phosphorus/g dry lung, n = 10; control: 228 +/- 9, n = 5) or the amount that was disaturated (tolerant: 44.7 +/- 4.2%, n = 5; control 45.0 +/- 2.1%, n = 4), there were marked increases in the relative amounts of phosphatidylcholine and phosphatidylethanolamine in the lavage from tolerant rats. Static compliance measurements revealed that the pressure required to maintain the tolerant lungs at 50% of total lung capacity was half that required in the control rats. At this stage it is not possible to say what role, if any, these changes have in the induction of tolerance to 100% oxygen.

Animals↗
PubMed1980

Spectrophotometric measurements of transmembrane potential and pH gradients in chromaffin granules.

The electrical potential (delta psi) and proton gradient (alpha pH) across the membranes of isolated bovine chromaffin granules and ghosts were simultaneously and quantitatively measured by using the membrane-permeable dyes 3,3'dipropyl-2,2'thiadicarbocyanine (diS-C3-(5)) to measure delta psi and 9-aminoacridine or atebrin to measure delta pH. Increases or decreases in the delta psi across the granular membrane could be monitored by fluorescence or transmittance changes of diS-C3-(5). Calibration of the delta psi was achieved by utilization of the endogenous K+ and H+ gradients, and valinomycin or carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP), respectively, with the optical response of diS-C3-(5) varying linearly with the Nernst potential for H+ and K+ over the range -60 to +90 mV. The addition of chromaffin granules to a medium including 9-aminoacridine or atebrin resulted in a rapid quenching of the dye fluorescence, which could be reversed by agents known to cause collapse of pH gradients. From the magnitude of the quenching and the intragranular water space, it was possible to calculate the magnitude of the alpha pH across the chromaffin granule membrane. The time-course of the potential-dependent transmittance response of diS-C3-(5) and the delta pH-dependent fluorescence of the acridine dyes were studied simultaneously and quantitatively by using intact and ghost granules under a wide variety of experimental conditions. These results suggest that membrane-permeable dyes provide an accurate method for the kinetic measurement of delta pH and delta psi in an amine containing subcellular organelle.

Acridines↗
PubMed1980

The misunderstood Spanish-speaking patient.

The authors examined the reactions of Spanish-speaking patients and of therapists to initial therapy interviews conducted with or without an interpreter. Twenty-one patients who used an interpreter, 40 bilingual patients, and the 16 psychiatric residents who conducted the interviews completed questionnaires aimed at evaluating therapy and communication effectiveness. A number of patient and therapist perceptions were significantly different. Patients interviewed with interpreters felt understood and helped and wanted to return, whereas the therapists responded that patients seen with interpreters felt less understood and less helped and did not want to return. The authors recommend more bilingual/bicultural therapists and an effort to help present therapists realize how valuable their efforts with patients who need an interpreter are.

Ambulatory Care↗
PubMed1979

Biological amine transport in chromaffin ghosts. Coupling to the transmembrane proton and potential gradients.

The effect of the transmembrane proton gradient (delta pH) and potential gradient (delta psi) upon the rate and extent of amine accumulation was investigated in chromaffin ghosts. The chromaffin ghosts were formed by hypo-osmotic lysis of isolated bovine chromaffin granules and extensive dialysis in order to remove intragranular binding components and dissipate the endogenous electrochemical gradients. Upon ATP addition to suspensions of chromaffin ghosts, a transmembrane proton gradient alone, a transmembrane gradient alone, or both, could be established, depending upon the compositions of the media in which the ghosts were formed and resuspended. When chloride was present in the medium, addition of ATP resulted in the generation of a transmembrane proton gradient, acidic inside of 1 pH unit (measured by [14C]methylamine distribution), and no transmembrane potential (measured by [14C]-thiocyanate distribution). When ATP was added to chromaffin ghosts suspended in a medium in which chloride was substituted by isethionate, a transmembrane potential, inside positive, of 45 mV and no transmembrane proton gradient, was measured. In each medium, the addition of agents known to affect proton or potential gradients, respectively, exerted a predictable mechanism of action. Accumulation of [14C]epinephrine or [14C]5-hydroxytryptamine was over 1 order of magnitude greater in the presence of the transmembrane proton gradient or the transmembrane potential than in the absence of any gradient and, moreover, was related to the magnitude of the proton or potential gradient in a dose-dependent manner. When ghosts were added to a medium containing chloride and isethionate, both a delta pH and delta psi could be generated upon addition of ATP. In this preparation, the maximal rate of amine accumulation was observed. The results indicate that amine accumulation into chromaffin ghosts can occur in the presence of either a transmembrane proton gradient, or a transmembrane potential gradient, and that the maximal rate of accumulation may exist when both components of the protonmotive force are present.

Adenosine Triphosphate↗