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S Dissing

Publications and source records attributed to S Dissing.

45 records · Page 3Linked to original sources
PubMed1989

Cholinergic-induced HCO3- loss from rat parotid acini.

The effect of cholinergic stimulation on the magnitude of anion loss from collagenase-isolated rat parotid acini suspended in a Krebs-Ringer bicarbonate buffer was characterized by means of 36Cl. It was found that on stimulation, the acinar Cl- concentration decreases from 62.3 mM to 22.6 mM in about 10 seconds after addition of carbachol. Concomitant with the dramatic net loss of Cl- a transient fall in the intracellular pH (pHi) of 0.1 pH-units occurred and that was interpreted as being due to acinar loss of HCO3-. The magnitude of the HCO3- loss was estimated in two different ways. From calculation of the intracellular buffer capacity at the unstimulated pHi of 7.28 it was found that the stimulation-induced fall of 0.1 pH-units is due to an efflux of about 5.5 mM from the acini. Another estimate of the HCO3- loss was based on the assumption that the ratio of HCO3- distribution on the internal and external sites of the plasma membranes is distributed according to the ratio for Cl-. By this calculation a HCO3- loss of 5.6 mM was found, which is in good accordance with the value obtained from the change in pHi. It was concluded that on cholinergic stimulation the acinar cells within seconds produce an isotonic fluid containing Cl- as the predominant anion and a small amount of HCO3-.

Animals↗
PubMed1988

Cholinergic-induced electrolyte transport in rat parotid acini.

Secretory responses of parotid acini occurring within 10 sec following cholinergic stimulation were characterized. 1. Measurement of membrane potentials by means of the fluorescent dye diSC3-(5) revealed a value of approximately -59 mV, which remained unaffected on stimulation. 2. Stimulation caused a rapid net loss of 42K+ that was strongly inhibited by the "maxi" K+-channel inhibitor "charybdotoxin" present in scorpion venom. 3. It was calculated that the number of open "maxi" K+-channels per cell was approximately 40 in the unstimulated state and approximately 3000 in the stimulated state. 4. Stimulation caused a transient decrease in the acinar ATP content. 5. Intracellular pH (pHi) measured by means of the fluorescent dye, BCECF, was dependent upon the presence of extracellular HCO3- as well as Na+. Under physiological conditions pHi was 7.27 and stimulation caused a transient decrease of 0.1 pH units due to HCO3- efflux. The decrease was followed by pHi recovery mediated by a Na+/H+ exchange mechanism.

Adenosine Triphosphate↗
PubMed1988

K+ transport and membrane potentials in isolated rat parotid acini.

42K+ transport properties of isolated rat parotid acini were characterized concomitant with measurements of membrane potentials (Em) by means of the fluorescent dye diSC3-(5). In unstimulated acini suspended in a 5 mM K+ buffer, Em was governed by the K+ and Cl- gradients and amounted to about -59 mV, a value that remained unaffected on cholinergic stimulation. In unstimulated acini, 42K+ influx was largely mediated by the Na+-K+ pump, and the residual influxes were mediated by a bumetanide-sensitive component (cotransport system) and by K+ channels. Efflux of 42K+ was largely mediated by a bumetanide-sensitive component and by K+ channels. In the unstimulated state, the cotransport system was mediating K+-K+ exchange without contributing to the net uptake of K+. Within 10 s after stimulation, a approximately 10-fold increase in the acinar K+ conductance (gK) occurred, resulting in a rapid net efflux of K+ that amounted to approximately 3.8 mmol.l cells-1.s-1. Measurements of 42K+ fluxes as a function of the external K+ concentration revealed that in the stimulated state gK increases when external K+ is raised from 0.7 to 10 mM, consistent with an activation of acinar gK by the binding of external K+ to the channel. 42K+ flux ratios as well as the effect of the K+ channel inhibitor from scorpion venom (LQV) suggest that approximately 90% of K+ transport in the stimulated state is mediated by "maxi" K+ channels.

Animals↗
PubMed1987

Stimulation-induced changes in cytosolic calcium in rat parotid acini.

The concentration of cytosolic, free calcium (Ca2+i) in collagenase-isolated rat parotid acini was measured by use of the fluorescent dye fura-2 (G. Grynkiewicz, M. Poenie, and R. Y. Tsien, J. Biol. Chem. 260: 3440-3450, 1985). Ca2+i was measured in unstimulated acini and in acini stimulated with cholinergic, alpha-adrenergic, and beta-adrenergic agonists, respectively. In unstimulated acini suspended in 1 mM Ca media, Ca2+i amounted to 155 +/- 38 nM (mean +/- SD, n = 14). After stimulation with the cholinergic agonist carbachol, Ca2+i increased transiently with a peak value of 640 +/- 90 nM (n = 3) obtained 4-6 s after stimulation. The peak value of Ca2+i was reduced when the extracellular calcium concentration decreased, and at 2 nM external calcium, Ca2+i amounted to 50% of the peak value observed at 1 mM external calcium. It was calculated that at least 50% of the rise in Ca2+i observed under physiological conditions (1 mM external calcium) after cholinergic stimulation is due to calcium mobilizations from intracellular pools. Stimulation with the nonspecific adrenergic agonist adrenaline caused a rise in Ca2+i of a similar magnitude as the rise observed after cholinergic stimulation. However, stimulations with the alpha-adrenergic agonist phenylephrine and the beta-adrenergic agonist isoproterenol caused a rise in Ca2+i amounting to 60 and 10%, respectively, of the rise observed after cholinergic or adrenergic stimulation.

Animals↗
PubMed1984

Chloride transport properties of human leukemic cell lines K562 and HL60.

The Cl- transport characteristics of the human leukemic cell lines K562 and HL60, with erythroid and granulocytic phenotypic features, respectively, were investigated. Cl- effluxes were measured with 36Cl- under equilibrium conditions in both cell lines and were found to be three orders of magnitude slower than the unidirectional efflux of Cl- in normal erythrocytes. Induction of differentiation of the K562 cell line with hemin does not affect the rate of Cl- transport, while induction of the HL60 cell line with dimethyl sulfoxide results in a small decrease in the rate of Cl- transport. Cl- transport in both cell lines could be divided into two components. One component is inhibited by treatment with 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), displays counter-transport characteristics, and has a high energy of activation--all properties characteristic of the human erythrocyte-facilitated anion exchange system. The second component is insensitive to DIDS, is partially inhibited by furosemide, and has a low energy of activation.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1981

The kinetics of anion equilibrium exchange across the red blood cell membrane as measured by means of 35S thiocyanate.

Up to a SCN- concentration of about 110 mM, the concentration dependence of SCN- equilibrium exchange in human red cell ghosts can be represented by the superimposition of two flux components. One component shows saturation kinetics, the other does not. The saturable component has an activation enthalpy of 105 kJ/mole, exhibits a trans acceleration by Cl- and can be inhibited by H2DIDS. The nonsaturable component has a much lower activation enthalpy of 33 kJ/mole, is slightly reduced in trans acceleration experiments with Cl- and insensitive to H2DIDS but susceptible to inhibition by phloretin. At SCN- concentrations exceeding 110 mM, the saturable component undergoes irreversible self inhibition while the nonsaturable component remains unaltered. The half saturation concentration of the saturable flux component increases with decreasing pH from 3.0 mM at pH 7.4 to 13.3 mM at pH 6.0. Over this pH range, the maximal flux is only slightly increased from 19 x 10(-12) to 22 x 10(-12) moles x cm-2 x sec-1. The nonsaturable flux component also increases slightly. In accordance with previous observations of Wieth (J. Physiol. (London) 207:563-580, 1970), we find that SCN- increases K+ and Na+ permeability. The induced cation-permeability is considerably smaller than the SCN- exchange and the latter does not show the paradoxical temperature dependence that is known to pertain to the former.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1979

Fluorescence labeling of the human erythrocyte anion transport system.

The anion transport system of human red cells was isolated in vesicles containing the original membrane lipids and the 95 000 dalton polypeptides (band 3) by the method of Wolosin et al. (J. Biol. Chem. (1977) 252, 2419--2427). The vesicles have a functional anion transprot system since they display sulfate transport that is inhibited by the fluorescent probe 8-anilinonaphthalene 1-sulfonate (ANS) with similar potency as in red cells. The vesicles were labeled with the SH-specific probe fluorescein mercuric acetate (FMA). Labeling lowers FMA fluorescence, and is prevented or reversed by dithiothreitol, suggesting that the reaction is with a thiol group on the protein. Fluorescnece titrations show a maximum labeling stoichiometry of 1.3 +/- 0.4 mol FMA/mol 95 000 dalton polypeptide. The polarization of bound FMA fluorescence is high indicating that the probe is highly immobilized. Pretreatment with Cu2+ + o-phenanthroline under conditions that crosslink band 3 in ghosts decreases FMA labeling 50%. Differences in kinetics of FMA labeling in sealed and leaky vesicles suggest that the reactive SH group is located in the intravesicular portion of the protein (corresponding to the cytoplasmic surface of the red cell) and that FMA can cross the membrane. Inhibitors of anion transport have no effect on FMA labeling kinetics suggesting it is not transported via the anion transport system. Sulfate transport in the labeled vesicles remains fully functional. We detected self-energy transfer between bound FMA molecules by fluorescence depolarization. With excitation at 450--50 nm P decreases from 0.4, when less than half of the proteins are labeled, to 0.1 at saturation. This depolarization is not observed with red edge excitation (510--530 nm). Addition of 0.1% sodium dodecyl sulfate (SDS) changes P to 0.32, regardless of the excitation wavelength or degree of saturation with FMA. These results indicate that the band 3 proteins are close enough to allow energy transfer between fluorophores(Ro = 37.4 A), which does not occur upon red edge excitation or when the proteins are separated by SDS. We conclude that the functional anion transport system exists as a dimer or higher oligomer of band 3 proteins in these membranes, confirming previous suggestions derived using other methods. Future applications are discussed.

Anilino Naphthalenesulfonates↗