PubMed Health⌕ Search

Biomedical subjects

J F Hoffman

Publications and source records attributed to J F Hoffman.

At least 73 records · Page 4Linked to original sources
PubMed1976

Comparison of the side-dependent effects of Na and K on orthophosphate-, UTP-, and ATP-promoted ouabain binding to reconstituted human red blood cell ghosts.

This paper is concerned with analyzing the sidedness of action of various determinants which alter the rate of ouabain binding to human red blood cell ghosts. Thus, ouabain binding promoted by orthophosphate (Pi) and its inhibition by Na are shown to be due to inside Pi and inside Na. External K inhibits Pi-promoted ouabain binding and Nao acts to decrease the effectiveness of Ko. Similarly, inside uridine triphosphate (UTPi) stimulates the rate of ouabain binding which can be antagonized by either Nai or Ko acting alone. The actions of Nai and Ko are different when ouabain binding is promoted by Pi and UTPi compared to inside adenosine triphosphate (ATPi). With ATPi, the ouabain binding rate is only affected when Nai and Ko are both present. Possible differences in the mechanism of action of K and Na on Pi-and UTP-promoted binding are discussed in the light of their sidedness of action.

Adenosine Triphosphate↗
PubMed1976

Effects of Mg and Ca on the side dependencies of Na and K on ouabain binding to red blood cell ghosts and the control of Na transport by internal Mg.

The effect of alteration in the concentration of internal Mg on the rate of ouabain binding to reconstituted human red blood cell ghosts has been evaluated as well as the effect of Mgi on Na:Na compared to Na:K exchange. It was found that the dependence of the rate of ATP-promoted ouabain binding on the combined presence of Nai and Ko which occurs at high [Mg]i is lost when the concentration of Mgi is lowered. The sensitivity of the external surface for Ko is also changed since Ko can now inhibit the ouabain binding rate in the absence of Nai; on the other hand Nao at low [Mg]i can stimulate ouabain binding indicating that the relative affinity of the outside surface for Nao has either increased or that for Ko has decreased or both. Thus the effects of changes in [Mg]i result in a change in the side-dependent actions of Na and K and emphasize the possible difficulties of interpreting results obtained on systems lacking sidedness. Mgi was found to be required for Pi-promoted ouabain binding and that the inhibitory action of Nai increased as [Mg]i was increased. In addition, Ca was found to be most effective in inhibiting the rate of ATP-promoted ouabain binding when Na and K were present together than when either was present alone. Na:K exchange was found to be more sensitive to the concentration of Mgi than Na:Na exchange; at low [Mg]i Na:K exchange could be stimulated without changing the extent of Na:Na exchange. These results are consistent with the idea that conformational states of the pump complex are directly influenced by [Mg]i.

Adenosine Triphosphate↗
PubMed1975

[Paroxysmal tachycardic atrial fibrillation: termination by surgically induced A-V block (author's transl)].

In a 58-year-old patient frequent attacks of tachycardic atrial fibrillation had given rise to signs of abnormal cardiac function. All drug treatment had failed, as had several attempts at electric countershock and rapid atrial and ventricular stimulation. For this reason a surgical A-V block at the level of the His bundle was induced under cardio-pulmonary bypass and a ventricular pacemaker inserted. One year postoperatively the pacemaker functions without complication, and the patient is without symptoms. The ECG shows no sign of spontaneous A-V conduction. This is thought to be the first report of surgically induced A-V block for the control of atrial fibrillation.

Atrial Fibrillation↗
PubMed1975

[Clinical and haemodynamic results with intra-aortic counterpulsation (author's transl)].

The AVCO balloon pump (model 7) was used on 13 patients with cardiogenic shock and for circulatory support after open-heart surgery. Twelve patients survived, but one patient died of a cerebral embolism which had occurred before the use of the balloon pump. Mean systemic arterial pressure, mean pulmonary artery pressure, pulmonary wedge pressure and heart rate were measured in all patients, while cardiac index and arterio-venous oxygen difference were measured in seven. Average duration of counterpulsation was four days. Vasopressor treatment was reduced or discontinued in all patients, urinary output increased markedly and the clinical state improved. Although systolic pressure did not change significantly, MAP increased significantly by 25 mm Hg (P less than 0.005), with a mean diastolic pressure increase to 104 mm Hg. The pulmonary artery pressure, the pulmonary wedge pressure and the mean pulse rate all decreased significantly by 25 mm Hg, 16 mm Hg and 24 beats/min, respectively. A fall in arterio-venous oxygen difference of 2.6 ml/100 ml (P less than 0.025) was associated with a significant increase in cardiac index by 0.62 l/min-m2 (P less than 0.025). It is concluded from these results that intra-aortic balloon counter-pulsation may be an effective means of providing circulatory support in cardiogenic shock and after open-heart surgery.

Arteries↗
PubMed1974

Interactions of a photo-affinity ATP analog with cation-stimulated adenosine triphosphatases of human red cell membranes.

To identify and isolate ATP binding and hydrolyzing sites of human red cell membranes we have synthesized a photo-activated ATP analog, 8-azido adenosine triphosphate (N(3)ATP). In the absence of ultraviolet light it is a substrate for both the Mg-ATPase and the ouabain-sensitive, Na,K-ATPase. Hydrolysis of N(3)ATP is prevented by increasing concentrations of ATP. Photolysis of N(3)ATP with red cell membranes results in covalent incorporation and irreversible inhibition of both ATPase activities. Also, only three protein components of the red cell membranes are labeled. This labeling is completely abolished by appropriate concentrations of ATP.

Adenosine Triphosphatases↗
PubMed1974

Chemical characterization and pronase susceptibility of the Na:K pump-associated phosphoprotein of human red blood cells.

The phosphoproteins formed by incubation of red cell ghosts with [gamma-(32)P]ATP in the presence of Mg and Na + Mg have been characterized by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The (32)P-labeled phosphoprotein was seen as a single peak confined to the region of the diffuse 90,000 dalton polypeptide band; labeling with Na + Mg considerably increased the quantity of (32)P-phosphoprotein contained in this band relative to labeling with Mg alone. Treatment of intact cells with Pronase known to partially hydrolyze the glycoproteins and the 90,000 daltons polypeptide did not change either the amount or the position of the (32)P-phosphoprotein present in the gels. The molecular weight of the (32)P-phosphoprotein is estimated to be 103,000. Pronase treatment of intact cells also did not significantly alter any of the transport parameters of the membrane such as the K pump flux, ouabain binding, or Na,K-ATPase. In contrast, treatment of ghosts with Pronase not only resulted in drastic alteration of the transport parameters but also inhibited the formation of the phosphoprotein under all conditions. Thus, while the Na:K pump is not intrinsically resistant to Pronase, those elements of the pump which are susceptible are not accessible from the outside of the cell. Further, SDS-polyacrylamide gel electrophoresis after Pronase treatment of intact cells results in a substantial increase in the purification of the phosphoprotein relative to that which was previously possible in ghosts.

Adenosine Triphosphatases↗
PubMed1974

Electrophoretic separation of different phophosproteins associated with Ca-ATPase and Na, K-ATPase in human red cell ghosts.

Ca has been found to increase the quantity of (32)P incorporated into red cell ghosts from [gamma-(32)P]ATP over the levels obtained by incubation with Mg alone or with Mg + Na, in correlation with the effect of Ca on the associated ATPase activities. When the (32)P-labeled ghosts were solubilized in sodium dodecyl sulfate (SDS) and electrophoresed on acrylamide gels only two bands could be detected either by autoradiography or by counting the sliced gels. The faster moving band (P-2) had the same mobility and the same molecular weight (103,000) as the phosphoprotein found either with Mg alone or with Mg + Na. The slower moving band (P-1) was not found in extensively washed ghosts labeled in the absence of Ca. The molecular weight of P-1 is approximately 150,000. P-1 like P-2 was not affected by pretreatment of intact cells with Pronase before labeling indicating that neither the phosphorylating mechanism nor the phosphoprotein are accessible to externally applied Pronase. The demonstration that a Ca-phosphoprotein is separable from the Na-stimulated phosphoprotein suggests that the Ca-ATPase is distinct from and independent of the Na,K-ATPase. The fact that Ca blocks the dephosphorylation by K of the Na-phosphoprotein indicates that caution is required in interpreting results when the activities of the different phosphoproteins have not been separately determined.

Adenosine Triphosphatases↗
PubMed1974

Antibody-induced alterations in the kinetic characteristics of the Na:K pump in goat red blood cells.

The kinetic characteristics of the Na:K pump in high potassium (HK) and low potassium (LK) goat red cells were investigated after altering the intracellular cation concentrations. At low concentrations of intracellular K (K(c)), increasing K(c) at first stimulates the active K influx in HK cells, but at higher K(c) the pump is inhibited. These results suggest that in HK cells K(c) acts both at a stimulatory site at the inner aspect of the pump and by competition with intracellular Na (Na(c)) at the Na translocation sites. In LK cells, K(c) inhibits the active K influx and the sensitivity of LK cells to inhibition is much greater than the sensitivity of HK cells. Exposure of LK cells to an antibody (anti-L), raised in an HK sheep by injection of LK sheep cells, increased the active K influx at any given K(c). The effect of the antibody was greater at higher intracellular K concentrations, and in cells with very low concentrations of K the antibody had little effect on the pump rate. The failure of anti-L to stimulate the pump in low K(c) LK cells was not due to failure of the antibody to bind to the cells. Anti-L combining at the outer surface of the cell reduces the affinity of the pump at the inner surface for K at the inhibitory sites. The maximal pump rate in LK cells at optimal Na and K concentrations is less than the maximal pump rate of HK cells under the same circumstances.

Animals↗
PubMed1974

Interaction of HK and LK goat red blood cells with ouabain.

The characteristics of the interaction of Na-K pumps of high potassium (HK) and low potassium (LK) goat red blood cells with ouabain have been determined. The rate of inhibition by ouabain of the pump of HK cells is greater than the rate of inhibition of the pumps of LK cells. Treatment of LK cells with an antibody (anti-L) raised in HK sheep by injecting LK sheep red cells increases the rate of inhibition of the LK pumps by ouabain to that characteristic of HK pumps; reduction of intracellular K (K(c)) in LK cells increases the rate at which ouabain inhibits their pumps and exposure of these low K(c) cells to anti-L does not affect the rate of inhibition. There is considerable heterogeneity in the pumps of both HK and LK cells in the rate at which they interact with ouabain or the rate at which they pump or both. LK pumps which are sensitive to stimulation by anti-L bind ouabain less rapidly than the remainder of the LK pumps and exposure to antibody increases the rate at which ouabain binds to the sensitive pumps; the difference between the two types of pumps disappears if intracellular K is very low. The calculated number of ouabain molecules bound at 100% inhibition of the pump is about the same for HK and LK cells. Although exposure to anti-L increases the apparent number of ouabain binding sites in LK cells at normal K(c), it does not alter the apparent number of sites in LK cells when K(c) has been reduced.

Animals↗
PubMed1974

Determination of membrane potentials in human and Amphiuma red blood cells by means of fluorescent probe.

1. Changes in the fluorescent intensity of the dye, 3,3'-dihexyl-2,2'-oxacarbocyanine, added to suspensions of human and Amphiuma red blood cells were measured in parallel with changes in the membrane potentials of these cells. In these studies the membrane potential was altered in three different ways: by the addition of valinomycin to alter the ratio, P(K)/P(Cl), by a change in the pH of the medium to alter the ratio, Cl(c)/Cl(0), and by the substitution of impermeant anions for Cl(0) again to alter the ratio, Cl(c)/Cl(0). In each case hyperpolarization led to a decrease and depolarization to an increase in fluorescent intensity.2. The change in fluorescence with the addition of valinomycin was dependent on the concentration of K in both the cells and the medium. Changes in fluorescence were not observed when valinomycin was added to suspensions of frozen-thawed, haemoglobin-free ghosts with dye in KCl or NaCl solutions. Such changes were observed with reconstituted ghosts provided that there was a K concentration gradient across the membrane.3. From values of cellular K and the corresponding external K concentrations for which there were no changes in fluorescence with valinomycin, estimations of membrane potentials were made. The potential was -5 to -8 mV for the human red cell and -19 mV for Amphiuma. These values are in good agreement with the potentials estimated from the Cl ratios (-9 mV for human and -17 to -20 mV for Amphiuma) and from those obtained by direct electrical measurements (-15 mV for Amphiuma).4. Fluorescent intensity of the dye in suspensions of human red cells was shown to be a linear function of the log Cl(c)/Cl(0).5. The dye (2.9 x 10(-6)M) increased the inward rate constants for (24)Na (3-4-fold) and (42)K (0.5-2-fold) for human red cells. In addition, the dye was found to be haemolytic (5-6% in 1 hr) at 22 degrees C.6. In contrast, the dye did not alter the rate of (35)SO(4) efflux at 37 degrees C from human red cells previously equilibrated with a Cl-free SO(4) medium.7. The dye was also seen to interact with certain impermeant anions and other compounds, e.g. inhibitors of anion permeability, of interest. These interactions and other limitations of the use of this dye are discussed.

Animals↗