Substitution Of Choline For Sodium Research Articles

Neuromedin B and Gastrin-Releasing Peptide Excite Arcuate Nucleus Neuropeptide Y Neurons in a Novel Transgenic Mouse Expressing StrongRenillaGreen Fluorescent Protein in NPY Neurons

Neuropeptide Y (NPY) is one of the most widespread neuropeptides in the brain. Transgenic mice were generated that expressed bright Renilla green fluorescent protein (GFP) in most or all of the known NPY cells in the brain, which otherwise were not identifiable. GFP expression in NPY cells was confirmed with immunocytochemistry and single-cell reverse transcription-PCR. NPY neurons in the hypothalamic arcuate nucleus play an important role in energy homeostasis and endocrine control. Whole-cell patch clamp recording was used to study identified arcuate NPY cells. Primary agents that regulate energy balance include melanocortin receptor agonists, AgRP, and cannabinoids; none of these substances substantially influenced electrical properties of NPY neurons. In striking contrast, neuropeptides of the bombesin family, including gastrin-releasing peptide and neuromedin B, which are found in axons in the mediobasal hypothalamus and may also be released from the gut to signal the brain, showed strong direct excitatory actions at nanomolar levels on the NPY neurons, stronger than the actions of ghrelin and hypocretin/orexin. Bombesin-related peptides reduced input resistance and depolarized the membrane potential. The depolarization was attenuated by several factors: substitution of choline for sodium, extracellular Ni(2+), inclusion of BAPTA in the pipette, KB-R7943, and SKF96365. Reduced extracellular calcium enhanced the current, which reversed around -20 mV. Together, these data suggest two mechanisms, activation of nonselective cation channels and the sodium/calcium exchanger. Since both NPY and POMC neurons, which we also studied, are similarly directly excited by bombesin-like peptides, the peptides may function to initiate broad activation, rather than the cell-type selective activation or inhibition reported for many other compounds that modulate energy homeostasis.

Effects of cytochalasin B on calcium transport by 1,25(OH)2D3- or PTH-treated chick embryonic yolk sac in vitro and in vivo.

The present study was done to elucidate the mechanism(s) by which calcium is taken up or transported across the yolk sac membrane of the embryonic chick. We examined the effect of various inhibitors or experimental conditions on the uptake of calcium in vitro. Treatment with ouabain, verapamil, antimycin A and calcium ionophore A23187; substitution of choline for sodium or potassium in the buffer; or incubation of the tissue at 0 degree C had no significant effect on calcium uptake by the yolk sac membrane. Dinitrophenol (DNP) and lanthanum chloride (LaCl2) reduced 45Ca uptake from day 6 and 9 embryos by 15% and 30%, respectively. Cytochalasin B decreased the uptake of 45Ca in yolk sac membrane disks of day 6 embryos, but not in older embryos. The effects of cytochalasin B were explored further in embryos pretreated with either 1,25(OH)2D3 or PTH, both of which enhance calcium uptake. Cytochalasin B decreased calcium uptake in 9-day and 12-day vitamin D-treated embryos to about 60% of their hormone-enhanced level and also decreased PTH-stimulated 45Ca uptake into yolk sac disks by about 50% in embryos of all age groups tested. We also examined the effect of cytochalasin B on 45Ca transport across the yolk sac membrane in vivo. Cytochalasin B did not affect this transport in control (vehicle-treated) embryos. However, it significantly decreased the enhanced in vivo 45Ca transport in day-9 and -12 vitamin D-treated embryos approximately 30% and 45%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Blocking of the sodium channel by external Tris in the squid giant axon

The macroscopic current carried by Na + ions was recorded in voltage-clamped squid giant axons that were dialysed with a mixture of CsF and NaF, and bathed in chloride solutions in which the sodium current (1 Na ) was reduced by partly blocking the sodium channels with tetrodotoxin, or by replacing four fifths of the Na + either with choline or with tris buffer at pH 7.3. The permeability coefficient (TNa fast) for the fast-inactivating current was unchanged on substitution of choline for sodium in the bathing solution, but in the high-Tris bathing solution, TNa fagt was reduced in a voltage-dependent manner, so that the permeability relative to normal rose from 0.2 at —40 m V to 0.8 at +100 mV. The coefficie10t TNa non for the non-inactivating current behaved in a similar way, except that the permeability ratio fell between test potentials of —40 and + 10 mV instead of rising. The blocking effect of Tris was unaffected by temperature, but there was some interaction with that of internal tetramethylammonium ions.

Effects of phlorizin and sodium on glucose-elicited alterations of cell junctions in intestinal epithelia

Glucose alters absorptive cell tight junction structure and, as deduced from an impedance analysis model, diminishes tight junction resistance in the small intestine (J.R. Pappenheimer, J. Membr. Biol. 100: 137-148, 1987; and J.L. Madara and J.R. Pappenheimer, J. Membr. Biol. 100: 149-164, 1987). Here we provide further evidence in support of this hypothesis using the conventional approach of analysis of mucosal sheets mounted in Ussing chambers. This approach offers advantages for investigating underlying mechanisms, including the effects of ions and inhibitors on the regulation of intercellular junctions by glucose. We show that phlorizin blocks a resistance decrease elicited by glucose and demonstrate that substitution of choline for sodium also prevents the response. The dilatations in absorptive cell tight junctions that accompany this glucose-elicited response are similarly prevented by phlorizin exposure or sodium substitution. The effects of phlorizin on junctional permeability can also be demonstrated in vivo. Phlorizin reduces the transjunctional flux of creatinine in glucose-perfused intestines of anesthetized animals, even when account is taken of the reduction of fluid absorption caused by phlorizin. Last, in vivo perfusion studies suggest that although, at 25 mM luminal glucose, virtually all glucose absorption is transcellular, at a luminal glucose concentration of 125 mM approximately 30% of glucose absorption occurs paracellularly because of solvent drag across tight junctions of altered permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

In Vivo Substitution of Choline for Sodium Evokes a Selective Osmoinsensitive Increase of Extracellular Taurine in the Rat Hippocampus

Recent investigations have demonstrated that taurine and phosphoethanolamine (PEA) are the amino acids most sensitive to microdialysis-perfusion with reduced concentrations of NaCl. The aim of the present work was to assess the importance of Na+ deficiency in evoking this response. Further, the previously described selectivity of replacement of Cl- with acetate with respect to amino acid release was reinvestigated. The hippocampus of urethane-anesthetized rats was dialyzed with Krebs-Ringer bicarbonate buffer, and amino acid concentrations of the perfusate were determined. Choline chloride was then stepwise substituted for NaCl, and, in some cases, mannitol (122 mM) was included in low sodium-containing media. In other experiments, NaCl was replaced with sodium acetate. The dialysate levels of taurine increased selectively in response to Na+ substitution. The elevation of taurine was linearly related to the increase in choline chloride, and maximal levels amounted to 335% of basal levels. The increase in extracellular taurine was not inhibited by perfusion with medium made hyperosmotic with mannitol. Replacement of Cl- with acetate stimulated the release of taurine to 652% of resting levels. In addition, PEA levels increased to 250% of control concentration. Other amino acids were unaffected by Cl- substitution. The results show that taurine transport is considerably more sensitive to Na+ depletion than glutamate transport, which also is known to be Na+ dependent. The taurine increase evoked by low Na+ is not caused by cellular swelling as it was unaffected by hyperosmolar medium. Finally, substitution of acetate for Cl- causes a specific elevation of extracellular taurine and PEA, possibly as a result of cytotoxic edema.

Tetrodotoxin-unaffected depolarization of frog muscles induced by the venom of jellyfish (Genus aurelia).

In the isolated frog muscle, the proteinaceous venom extracted from jellyfish (genus Aurelia) produced 1) a complete and irreversible block of indirectly and directly elicited muscle twitch and 2) an irreversible depolarization of the muscle membrane. This venom-induced depolarization was effectively reversed or prevented by the substitution of choline for sodium in Ringer solution, but not by the introduction of tetrodotoxin (TTX), a sodium channel blocker. The mechanism of muscle membrane depolarization appears to involve probably an increase in membrane permeability to sodium ion as shown by the decrease in membrane resistance. These results suggest that the venom forms a pore which has sodium selectivity or activates a TTX-insensitive sodium channel which is different from the known sodium channel.

Action potentials in human macrophages are calcium spikes

Transmembrane resting and action potentials measured with single and double microelectrode impalements of human monocyte-derived macrophages reveal that repetitive action potentials induced by depolarizing current pulses are sodium insensitive and calcium dependent. Neither amplitude, frequency of spiking, threshold nor rate of rise of the action potentials is altered by different levels of extracellular sodium, substitution of choline for sodium, or exposure to tetrodotoxin. Spiking activity is enhanced in high calcium, diminished in frequency and amplitude by lowered extracellular calcium and is blocked by cobalt and verapamil.

Sodium-dependent relaxation in arterial smooth muscle.

1. The effects of isosmotic substitution of choline for sodium on resting tension and on relaxation after noradrenaline-induced contraction was studied in rabbit isolated aortic strips immersed in Hepes-buffered physiologic salt solution (PSS) warmed to 37 degrees C and gassed with 100% O2. 2. Isosmotic substitution of choline for sodium produced a sustained increase in resting tension which effectively prevented any evaluation of the influence of sodium on relaxation. The increase in resting tension was insensitive to 10(-8) mol/l atropine but was abolished by 10 min exposure to calcium-free PSS prior to replacement of sodium. 3. Under sodium-calcium free conditions which eliminated the increase in resting tension observed in sodium-free PSS, stimulation with 10(-5) mol/l noradrenaline initiated contractions that were 55 +/- 7.5% of the control response in normal PSS. Washout of noradrenaline with sodium-calcium-free PSS failed to produce any decrement in tension. However, restoration of the normal sodium resulted in gradual relaxation. 4. These results suggest that sodium is required for relaxation after noradrenaline-induce contraction of arterial smooth muscle.

Stopped-flow microperfusion studies of urate absorption from the rat proximal tubule.

AbstractThe absorptive flux of [2-14C]urate in the rat proximal tubule was examined using stopped-flow and continuous-flow microperfusion techniques. In the stopped-flow studies, the luminal perfusion was a steady-state equilibrium solution and the luminal contact time was 60 sec. The ratio of disintegrations per minute (dpm) of urate in the reaspirated sample to the initial solution (C/I) was 0.42 ± 0.02 in control experiments. The addition of either phloridzin or ρ-chloromercuribenzoate to the perfusion solution resulted in significantly higher C/I ratios of 0.52 ± 0.03 (P < 0.05) and 0.61 ± 0.006 (P < 0.01), respectively. Substitution of choline for sodium in the perfusion solution or the addition of probenecid did not significantly change the C/I ratio. In continuous-flow microperfusion studies, the fractional absorption of urate from an isotonic saline solution averaged 10.2 ± 0.8%/mm tubule and was significantly inhibited by the addition of probenecid to the perfusion solution. Urate absorption from...

Increased intestinal absorption in the rat caused by sodium lauryl sulphate, and its possible relation to the cAMP system

The increases in the absorption of ouabain, phenolsulphonphthalein and pralidoxime caused by 17 mM sodium lauryl sulphate (SLS) from jejunal loops of anaesthetized rats were significantly reduced if sodium and chloride (Briseid et al., 1974) or chloride and bicarbonate were replaced by other ions in the loop fluid. Separate substitutions of sodium, chloride of bicarbonate did not significantly alter the SLS-caused absorption, except that the substitution of choline for sodium reduced the absorption of pralidoxime, both in the presence and in the absence of SLS. The increases in the absorption of phenolsulphonphthalein and pralidoxime caused by SLS were potentiated by theophylline (25 mM) and reduced by imidazole (25 mM). The addition of dibutyryl cyclic AMP (2.5 mM) to the loop fluid increased this absorption of the test substances. This effect was reduced by imidazole, but under the experimental conditions it was not potentiated by theophylline. Determinations of cyclic AMP in the rat intestinal mucosa showed that the level of this substance was significantly higher in the presence than in the absence of SLS. The experimental conditions were as described for the absorption experiments. It is concluded that the data obtained support the idea of an increased level of cyclic AMP as the main basis for the effect of SLS on the absorption.

Aconitine-induced repetitive firing in frog skeletal muscle and the effect on cable properties

The repetitive firing in curarized frog sartorius muscle caused by aconitine was found to be associated with a dose-dependent membrane depolarization and a decrease in membrane resistance (R m). Shortly after aconitine treatment, when repetitive discharges began to occur spontaneously in a few fibers (the pre-burst state), the muscle fibers were hypersensitive to mechanical and electrical stimulation. After a repetitive discharge (the post-burst state), the membrane potential fell to the 40–50 mV range. Cable measurements demonstrated that R m decreased by 27% in the pre-burst state and by 47% in the post-burst state. Substitution of choline for sodium in the post-burst state restored the membrane potential to normal and raised the R m toward the control level. It is proposed that aconitine's production of repetitive discharges in skeletal muscle is partly the result of maintaining the sodium conductance g Na at a higher-than-normal level once excitation has been initiated.

The role of sodium pump in the inhibition of smooth muscle responsiveness to agonists during potassium restoration

1. Isometric contractions of cat splenic capsular smooth muscle in response to noradrenaline and histamine were recorded.2. Removal of potassium from the bathing medium did not change the resting tension or the responsiveness to noradrenaline. Restoration of potassium inhibited responses to noradrenaline or histamine only if the muscles were stimulated with an agonist while in the K-free medium.3. This inhibition of responses to the agonists due to potassium was reversed rapidly by removing the ion or reversed slowly by prolonged exposure to the ion. The inhibition was also blocked by procedures or agents which block the sodium pump (ouabain, substitution of NaCl by LiCl), inhibit active processes (low ambient temperature) or prevent intracellular accumulation of sodium (substitution of choline for sodium).4. It is proposed that under special circumstances such as when there is an increase in internal sodium concentration, the sodium pump is probably electrogenic and causes relaxation when activated by external potassium. In the normal muscle the pump is probably electrically neutral.

Changes in oxygen consumption of isolated tissues after ouabain administration or substitution of choline for sodium in bathing media

Changes in oxygen consumption of isolated tissues after ouabain administration or substitution of choline for sodium in bathing media

Calibration of Clark oxygen electrode for use in aqueous solutions.

ARTICLESCalibration of Clark oxygen electrode for use in aqueous solutionsM. E. LeFevreM. E. LeFevrePublished Online:01 Jun 1969https://doi.org/10.1152/jappl.1969.26.6.844MoreSectionsPDF (563 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByHyperbaric hyperoxia and normobaric reoxygenation increase excitability and activate oxygen-induced potentiation in CA1 hippocampal neuronsAlfredo J. Garcia, Robert W. Putnam, and Jay B. Dean1 September 2010 | Journal of Applied Physiology, Vol. 109, No. 3Adaptation of Polarographic Oxygen Sensors for Biochemical Assays31 October 2006Effects of ouabain and high K+ on respiration of turtle brain and urinary bladder in vitroComparative Biochemistry and Physiology Part A: Physiology, Vol. 45, No. 2Induction of tissue swelling by alteration of orientation of tissue sacsComparative Biochemistry and Physiology Part A: Physiology, Vol. 41, No. 2Changes in oxygen consumption of isolated tissues after ouabain administration or substitution of choline for sodium in bathing mediaBiochimica et Biophysica Acta (BBA) - General Subjects, Vol. 222, No. 1 More from this issue > Volume 26Issue 6June 1969Pages 844-846 Copyright & PermissionsCopyright © 1969 the American Physiological Societyhttps://doi.org/10.1152/jappl.1969.26.6.844PubMed5786419History Published online 1 June 1969 Published in print 1 June 1969 Metrics

Effect of ouabain on ion transport mechanisms in the isolated turtle bladder.

Effect of ouabain on ion transport mechanisms in the isolated turtle bladder.

THE EFFECTS OF VASOPRESSIN ON THE SHORTCIRCUIT CURRENT ACROSS THE WALL OF THE ISOLATED BLADDER OF THE TOAD, BUFO MARINUS

SUMMARY 1. The effects of metabolic inhibitors and ionic changes on the short-circuit current across the toad's bladder have been studied both in the presence and absence of vasopressin. 2. The effects of metabolic inhibitors indicate that the energy for short-circuit current is derived from both glycolysis and oxidative metabolism. 3. Divalent ions play an important part in the maintenance of the resting short-circuit current and of its response to vasopressin. Ca++ or Sr++ are necessary for the former and Ca++ for the latter. 4. Increased concentration of Ca++, Sr++, Mg++ or Ba++ did not inhibit the increment in short-circuit current produced by vasopressin, in contrast to the effect of these ions on water transport. 5. Increase and decrease in potassium concentration inhibited the short-circuit current whether vasopressin was present or not. 6. The correct concentration of sodium on the serosal side of the bladder was necessary to maintain the short-circuit current, but the increment seen when vasopressin was added was not affected by 50% substitution of choline for sodium.