Direct measurement of Na influx by 23Na NMR during secretion with acetylcholine in perfused rat mandibular gland

In-cell NMR: Why and how?

NMR spectroscopy has been applied to cells and tissues analysis since its beginnings, as early as 1950. We have attempted to gather here in a didactic fashion the broad diversity of data and ideas that emerged from NMR investigations on living cells. Covering a large proportion of the periodic table, NMR spectroscopy permits scrutiny of a great variety of atomic nuclei in all living organisms non-invasively. It has thus provided quantitative information on cellular atoms and their chemical environment, dynamics, or interactions. We will show that NMR studies have generated valuable knowledge on a vast array of cellular molecules and events, from water, salts, metabolites, cell walls, proteins, nucleic acids, drugs and drug targets, to pH, redox equilibria and chemical reactions. The characterization of such a multitude of objects at the atomic scale has thus shaped our mental representation of cellular life at multiple levels, together with major techniques like mass-spectrometry or microscopies. NMR studies on cells has accompanied the developments of MRI and metabolomics, and various subfields have flourished, coined with appealing names: fluxomics, foodomics, MRI and MRS (i.e. imaging and localized spectroscopy of living tissues, respectively), whole-cell NMR, on-cell ligand-based NMR, systems NMR, cellular structural biology, in-cell NMR… All these have not grown separately, but rather by reinforcing each other like a braided trunk. Hence, we try here to provide an analytical account of a large ensemble of intricately linked approaches, whose integration has been and will be key to their success. We present extensive overviews, firstly on the various types of information provided by NMR in a cellular environment (the "why", oriented towards a broad readership), and secondly on the employed NMR techniques and setups (the "how", where we discuss the past, current and future methods). Each subsection is constructed as a historical anthology, showing how the intrinsic properties of NMR spectroscopy and its developments structured the accessible knowledge on cellular phenomena. Using this systematic approach, we sought i) to make this review accessible to the broadest audience and ii) to highlight some early techniques that may find renewed interest. Finally, we present a brief discussion on what may be potential and desirable developments in the context of integrative studies in biology.

HCO3(-)-dependent ACh-activated Na+ influx in sheep parotid secretory endpieces

In the present study we used the Na)+)-sensitive fluorescent dye SBFI and optical measurement of endpiece volume to investigate the transport of Na+ in sheep parotid secretory cells. Sheep parotid endpiece cells bathed in a HCO3(-)-free Cl(-)-rich solution had a resting intracellular Na+ concentration ([Na+]i) of 17 +/- 2 mmol/l (n = 39). Exposure of the cells to a 2-min pulse of acetylcholine (ACh) (3 x 10(-7) mol/l) in a HCO3(-)-free bathing solution produced no change in [Na+]i or in cell volume. Changing from a Cl(-)-containing HCO(3-)-free bath solution to a Cl- solution containing 25 mmol/l HCO3- caused the endpieces to swell by 8 +/- 2% (n = 11) and the [Na+]i to increase by 10 +/- 2 mmol/l (n = 14). Subsequent exposure of the cells to ACh led to shrinkage of the cells by 12 +/- 2% from the volume in the HCO3(-)-containing solution prior to ACh exposure, with the maximum decrease occurring after 29 +/- 7 s (n = 9). This shrinkage was accompanied by a rapid and transient increase in [Na+]i, the [Na+]i reaching a peak at 70 +/- 5 mmol/l above the unstimulated level (n = 9). Substitution of gluconate for Cl- did not significantly alter the effects of HCO3- on unstimulated [Na+]i or endpiece volume, nor did it significantly inhibit the effects of ACh on these two parameters when HCO3- was present.(ABSTRACT TRUNCATED AT 250 WORDS)

A review of electron probe X-ray microanalysis studies of salivary gland cells

Electron probe X-ray microanalysis (EPXMA) has now been successfully applied to several salivary gland preparations. This paper briefly reviews the principles underlying this technique and the specific sample preparation procedures which permit accurate measurement of elemental concentrations in the various intracellular spaces. Findings from salivary gland studies indicate that cytoplasmic and nuclear spaces of nonstimulated acinar cells have high concentrations of K and P, and low concentrations of Mg, Ca, and S; and that mature secretory granules have high concentrations of Ca and S, and relatively low concentrations of K and P. No consistent differences have been found between the elemental concentrations of mucous and serous secretory granules. In vivo and in vitro EPXMA studies of the elemental changes associated with secretory granule maturation indicate there are at least two stages in this process: an early stage during which granule S concentration increases in parallel with mass density as condensing vacuoles mature into secretory granules, and a late stage during which granule mass density and protein content increase with no further elemental concentration changes. Findings from other in vivo and in vitro studies indicate that secretory granule membranes are permeable to Na, K, and Cl ions because the granular concentrations of these elements are altered by electrochemical gradients. Recent EPXMA results indicate that cells stimulated with parasympathomimetic agonists have decreased K and Cl concentrations, and increased Na concentrations. Furthermore, the magnitude of these changes are quantitatively consistent with changes measured using radio-isotope equilibration and other techniques. In contrast, cells stimulated with the beta-adrenergic agonist, isoproterenol, have increased concentrations of Na and Cl, but unchanged K concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

An analysis of intracellular 23Na relaxation using the double-quantum filtered NMR signal from the perfused rat salivary gland

The intracellular sodium of the perfused rat mandibular salivary gland was measured by double-quantum filtered 23Na-NMR spectroscopy at 2.34, 4.7 and 8.45 T. Biexponential relaxation of the intracellular 23Na signal was observed, and its intensity was increased by administration of acetylcholine with ouabain at 25 degrees C. The transverse and longitudinal relaxation rate constants were determined by the 'transverse experiment' (D-90 degrees-tau/2-180 degrees-tau/2-90 degrees-delta-90 degrees-acquire) and the 'longitudinal experiment' (D-180 degrees-tau-54.7 degrees-delta-90 degrees-acquire), respectively. From observed dependencies on B0 and temperature (5-37 degrees C), a possibility of exchange between two populations of intracellular Na+ was suggested. A small fraction of Na+ is in the slow-motion condition (with a quadrupole coupling constant of approx. 1.75 MHz and a correlation time of 6 x 10(-8) s). The major portion of intracellular Na+ is in the extreme narrowing condition with a transverse relaxation rate constant of approx. 100 s-1, which corresponds to a viscosity of approx. 5 cP.

Oxygen consumption for K+ uptake during post-stimulatory activation of Na+, K(+)-ATPase in perfused rat mandibular gland

1. In order to determine the stoichiometry of K+ uptake and ATP consumption by Na+, K(+)-ATPase in the isolated, perfused mandibular gland of the rat, oxygen consumption and net K+ uptake from the vascular side were measured during the recovery period following K+ depletion by stimulation with acetylcholine in combination with ouabain. 2. Acetylcholine (10(-6) M) induced fluid secretion and an initial, transient release of K+ from the gland. Addition of ouabain suppressed salivary fluid secretion and caused an additional, dose-dependent, transient release of K+. 3. With acetylcholine (10(-6) M), the oxygen consumption of the gland increased to 62.4 +/- 4.2 microliters/(g min) from a resting value of 12.9 +/- 1.2 microliters/(g min). The increased oxygen consumption was suppressed by ouabain, in a dose-dependent fashion. 4. Withdrawal of acetylcholine and ouabain induced a net uptake of K+ and, simultaneously, an increase in oxygen consumption. The cumulative K+ uptake and the increment of oxygen consumption during the recovery period were dependent on the concentration of used ouabain. 5. The rates of K+ uptake and ATP hydrolysis were compared during recovery, assuming that six moles of ATP were hydrolysed for each mole of oxygen consumed. The data obtained during the later phase of the recovery lay on a single straight line with a slope of 1.8 for each of the various concentrations of ouabain, suggesting that the relationship between K+ uptake and energy consumption was linear. 6. Assuming the K+:ATP stoichiometry of the Na+, K(+)-ATPase to be 2:1, K+ would appear to be transported with ca 90% efficiency by Na+, K(+)-ATPase in the rat mandibular gland. Using 1.8-2.0 as a K+/ATP stoichiometry, the rate of primary active K+ uptake and the corresponding passive K+ efflux during secretion were estimated to be 20-22 mumol/(g min) from the oxygen consumption and the net K+ flux. 7. The passive K+ efflux was estimated, from the initial rate of K+ release caused by addition of 10(-3) M-ouabain, to be 30 mumol/g min). The discrepancy between the estimated active K+ uptake and passive K+ release (8-10 mumol/(g min] could be attributed to a secondary active K+ uptake process such as Na(+)-K(+)-2Cl-symport.

Direct measurement of K movement by 39K NMR in perfused rat mandibular salivary gland stimulated with acetylcholine

The intracellular K content (Kin) of the isolated perfused rat mandibular gland was measured by 39K NMR spectroscopy at 25 degrees C, using an inversion recovery technique based on the fact that the spin-lattice (T1) relaxation of Kin is much faster than that of the extracellular K. Kin decreased by 30-34% of the resting level and reached a plateau level during secretion evoked by a sustained infusion of 1 mumol/l acetylcholine. Addition of 1 mmol/l ouabain decreased Kin by an additional 41% of the resting level. The K net flux to the blood and saliva was calculated from the K concentrations and flow rates of the effluent and the saliva. At an initial stage of secretion the gland lost K to the vascular side at a rate of 12.6 +/- 1.8 mumol/g-min (mean +/- SEM, n = 7). During sustained secretion, the gland took K up from the vascular side at a rate of 3.3 +/- 0.7 mumol/g-min (n = 7), and the same amount of K was secreted into the saliva (4.7 +/- 1.1 at 5-10 min, 2.8 +/- 0.8 mumol/g-min at 20-30 min), resulting in no net K movement from the gland. Addition of 1 mmol/l ouabain stopped salivary secretion and caused a transient K release to the vascular side at a maximum rate of 12.8 +/- 1.1 mumol/g-min. Withdrawal of acetylcholine and ouabain induced K uptake from the vascular side (6.5 +/- 0.7 mumol/g-min) and the amount of K released was completely restored when Kin recovered completely.(ABSTRACT TRUNCATED AT 250 WORDS)

23Na NMR measurement of the maximal rate of active sodium efflux from human red blood cells

The method for 23Na NMR measurement of the maximal rate of active Na+ efflux from human red blood cells (RBC) is proposed. The nonpenetrating paramagnetic shift reagent (SR) bis(tripolyphosphate)dysprosium(III) complex is used to distinguish extracellular Na+ ions from intracellular. RBC are proved to retain their physiological activity in the presence of SR. Intracellular Na+ is shown to be 100% NMR visible. The levels of intracellular and extracellular Na+ and K+ ions are changed to decrease their concentration gradients across the erythrocyte membrane to make active Na+ efflux the only 23Na NMR measurable process; so the integrated areas of intra- and extracellular Na+ peaks remain invariant throughout the incubation period in the presence of 0.25 mM ouabain, a specific inhibitor of Na+, K+-ATPase. The accuracy of the proposed technique is evaluated to be 10%. The maximal Na+ efflux is determined to be 10.1 +/- 1.0 mM/h/liter of cells.