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PubMed1983

Localization of the major dehydrogenases in two methylotrophs by radiochemical labeling.

The localization of prominent proteins in intact cells of two methylotrophic bacteria, Hyphomicrobium sp. strain X and bacterium W3A1, was investigated by radiochemical labeling with [14C]isethionyl acetimidate. In bacterium W3A1, trimethylamine dehydrogenase was not labeled by the reagent and is, therefore, an intracellular protein, whereas the periplasmic location of the methylamine and methanol dehydrogenases was evidenced by being readily labeled in intact cells. Similarly, an intracellular location of the trimethylamine and dimethylamine dehydrogenases in Hyphomicrobium sp. strain X was indicated, whereas methanol dehydrogenase was periplasmic.

Alcohol Oxidoreductases↗
PubMed1986

Chloride removal and excitation-contraction coupling in guinea pig ileal smooth muscle.

The effect of extracellular Cl (Cl-o) removal on contractions evoked by a selective muscarinic agonist, cis-2-methyl-4-dimethylaminomethyl 1,3-dioxolane methiodide (CD), and high K+ depolarizations in the isolated guinea pig ileal longitudinal muscle was studied. The replacement of Cl-o with impermeant anions, such as isethionate (Ise-), was found to selectively inhibit a portion of the initial phasic response to K+ and CD, leaving the secondary and sustained tonic responses unchanged. In Ca2+-free solutions, the loss of contractile responses to high K+ was faster and more pronounced in Cl--free compared with Cl--containing solutions. Furthermore, the uptake of Ca2+, as represented by 45Ca2+, from the saline solution was delayed and reduced in Ise--containing Cl-o-free solutions. Replacement of Cl-o with other impermeant anions, such as gluconate and methylsulphate, had a similar action on contractile activity as for Ise-replacement. Cl-o replacement with permeant anions, such as nitrate, however, did not significantly inhibit the phasic response and sometimes increased the tonic response to K+. These results indicate that there is a Cl-o-dependent Ca2+ pool in the guinea pig ileal longitudinal muscle and we speculate that this Cl-o-dependent Ca2+ pool is associated with membrane structures, such as calveolae, which would thus offer a degree of protection to depletion by removal of extracellular Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Chloride and depolarization by acetylcholine in canine airway smooth muscle.

The role of chloride channels has been examined in canine tracheal smooth muscle by recording mechanical responses to field stimulation and to acetylcholine (ACh) and by sucrose gap recording of excitatory junction potentials and ACh-induced electrical changes. The results of substitution studies using isethionate for chloride provided evidence that a chloride conductance contributes to the resting potential. The extrapolated reversal potential for ACh-induced depolarization was positive to the resting potential. Isethionate substitution inhibited ACh-induced depolarization, consistent with a contribution from increased Cl- conductance to the depolarization induced by ACh. However, closure of K+ channels and opening of a non-specific cation channel could also contribute to depolarization. Further study of the effects of isethionate substitution during prolonged tissue exposure to chloride-free medium showed that retention or the accumulation of Ca2+ in intracellular stores was impaired. We conclude that effects of chloride deprivation on responses to ACh may reflect an early increase in Cl- conductance, but longer term changes reflect the requirement for this anion to maintain internal Ca2+ stores.

Acetylcholine↗
PubMed1989

Membrane effects of chloride substitutes in guinea pig gallbladder epithelial cells.

Differences in the responses of guinea pig gallbladder epithelial cells to replacement of luminal Cl- with either isethionate (I), gluconate (G), sulfate (S), or cyclamate (C) were investigated in vitro using intracellular microelectrode techniques. In prostaglandin E1 (PGE1)-treated tissues (10(-6) M, serosal side), where electrodiffusive apical membrane Cl- permeability (PCla) is high, replacement of luminal Cl- caused transient membrane depolarizations of similar magnitudes but different times to peak (C greater than G = S greater than I). The subsequent shifts in membrane voltages were, at steady state, straight correlated with the concomitant increases in apparent ratio of apical to basolateral membrane resistances (Ra/Rb). Increases followed the rank order I greater than G = S greater than C, which was also found to be the case in the peak membrane hyperpolarizations on restoring luminal Cl-. Under control conditions (no PGE1, low PCla), three of the substitutes caused a slow hyperpolarization, C greater than G = S, whereas an I-for-Cl- substitution evoked a transient depolarization and a drop in Ra/Rb. Under both control and PGE1 conditions, a transient depolarization followed luminal I-for-C substitution. Our results are best explained by a stimulatory effect of I (and, less marked, G and S) on PCla. Intrinsic effects of cyclamate are not ruled out; however, among the substitutes examined, it is the most inert.

Animals↗
PubMed1991

Electric properties of rat liver cell cultures on gas-permeable membranes.

In rat hepatocytes grown on gas-permeable membranes (Petzinger et al. In Vitro Cell. Dev. Biol. 24: 491-499, 1988), cellular and canalicular potentials as well as input resistances were measured using two-channel microelectrodes. In HCO3(-)-containing solutions, we found -30.9 +/- 0.4 (SE) (n = 141) and -13.9 +/- 1.4 mV (n = 22) for cell and canalicular membrane potentials, respectively. There was no dependence of these parameters on the age of the primary culture. Canalicular input resistance, however, increased from 13.3 +/- 2.0 M omega (n = 4) at day 1 after seeding to 36.1 +/- 5.0 M omega (n = 9) at day 2 and stabilized thereafter, while cell input resistance continuously decreased from 37.0 +/- 3.3 M omega at 1 h (n = 6) to 5.2 +/- 2.1 M omega (n = 27) at 3 days after preparation. In ion substitution experiments there were no changes in the transference numbers for K+, Na+, or Cl- that could account for this effect. Cable analysis, however, revealed that the decrease in input resistance reflects a time-dependent increase in electrical coupling between cells. We conclude that rat liver cells on gas-permeable membranes are highly suited for the quantitative analysis of cell-to-cell interaction. In addition, cells and canaliculi are readily accessible with two-channel microelectrodes, making this preparation a promising tool for electrophysiological analysis of hepatocellular transport mechanisms.

Animals↗
PubMed1975

Norepinephrine vascoconstrictor escape in isolated meseneric arteries.

When isolated superfused cat mesentric arterial rings were exposed to norepinephrine(NE) 10'-6 g/ml, force initially increased but subsequently declined despite continuedadministration of NE. Phasic contractions occurred in 48% of the vessels. Norepinephrine concentrations just above threshold induced tonic contractions without escape. When NE was administered after brief exposure of the arterial rings to low-calcium solutions, peak force development and escape were both reduced and phasic contractions were abolished. Escape did not occur in potassium-depolarized vessels. The peak response was increased and escape was reduced by substituting sodium in the Krebs solution by lithium and by substituting chloride with iodide or perchlorate. Substitution of chloride by isethionate reduced the peak NE resonse and abolished escape. Propanolol was without effect. It is suggested that escape from NE vasoconstriction in mesenteric arteries is due to fading of propagated activity.

Animals↗
PubMed1975

Ionic mechanisms of intestinal electrical control activity.

The effects of inhibition and stimulation of the electrogenic Na pump and of altering the ionic environment on the electrical control activity (ECA) were studied in rabbit jejunal smooth muscle. Pump inhibition abolished the ECA at a time when the membrane potential was more negative than the peak depolarization of the control potential (CP). Pump stimulation hyperpolarized the membrane and CP's appeared. Their amplitude was initially small and progressively increased as the hyperpolarization subsided. Lowering external Na to 20 mM or Ca withdrawal, but not addition of verapamil, reversibly abolished the ECA. Chloride replacement by propionate, isethionate, or benzene-sulphonate caused a transient augmentation, followed by suppression of the secondary depolarization of the CP's and decreased their frequency. The initial depolarization of the CP was little affected. Nitrate substitution increased CP frequency and spiking activity but had no observable effects on the CP configuration. These results suggest that the intestinal control potential may result from conductance changes initially to Na and later to C1 rather than fron an oscillatory electrogenic pump.

Animals↗
PubMed1977

Parasympathetic control of Na, K transport in perfused submaxillary duct of the rat.

The effects of stimulating the parasympathetic innervation to rat submaxillary gland on ductal transport of Na, K, water, and transepithelial PD, were tested in the main excretory duct during perfusion through its lumen. During nerve stimulation, transepithelial PD was consistently decreased, usually by about 15 mV, and this decrease could be blocked by atropine but not by adrenergic blocking agents. Net flux of Na, K, or water was not significantly changed during stimulation. One-way flux of Na from the lumen also was unaffected. The decrease in PD during stimulation was not affected by substituting isethionate for Cl or increasing [K] in the luminal perfusion medium. It is concluded that parasympathetic effects are exerted on the ductal cells, but that these probably do not involve conductance changes at the luminal membrane.

Animals↗
PubMed1984

Mechanism of bicarbonate exit across basolateral membrane of the rabbit proximal convoluted tubule.

To clarify the mechanism(s) of HCO-3 movement across the basolateral membrane, rabbit proximal convoluted tubules were perfused in vitro. Two possible mechanisms were examined: neutral HCO-3 exit coupled to chloride and rheogenic HCO-3 exit. A complete C1- substitution with isethionate in the lumen and bath did not affect HCO-3 reabsorption, suggesting that HCO-3 exit is not coupled to chloride. Addition of 2 mM Ba2+ to the bath, which has been shown to depolarize the basolateral membrane potential difference, caused a 42% inhibition of HCO-3 reabsorption and a 32% inhibition of volume flux, suggesting that HCO-3 exit is rheogenic. Ba2+ did not affect the volume flux when HCO-3 reabsorption was inhibited by acetazolamide, suggesting that the Ba2+ effect is not due to a general inhibition of cell metabolism. From these data we propose that HCO-3 exits the basolateral membrane by a rheogenic, chloride-independent mechanism.

Animals↗
PubMed1984

Anoxic cell swelling dissociated from excess permeability by poorly penetrating solutes.

Increased plasma membrane permeability, cell swelling, and cell death are consequences of metabolic energy deprivation. Rabbit retinas were incubated in an oxygenated artificial cerebrospinal fluid containing glucose. The incubating medium was modified by causing anoxia and glucose deprivation with one of the following treatments: addition of 97 mM mannitol, equimolar substitution of choline+ for Na+, or substitution of isethionate- for Cl-. Some retinas were resupplied with oxygen and glucose to determine the consequences of solute manipulation. Water compartments and membrane permeability were assayed using [3H]inulin and [14C]mannitol. Abnormal nuclei were counted on blind-coded slides. Both treatments prevented doubling of inulin-free water of untreated retinas after 70 min of deprivation. Neither treatment preserved morphology or prevented massive swelling after restoration of oxygen and glucose and gradual removal of the treatment. Mannitol leaked into deprived cells only, even when swelling was prevented. We conclude that prophylaxis of cell swelling during metabolic energy deprivation prevents neither cell leakiness nor cell death.

Aerobiosis↗
PubMed1992

Involvement of chloride in renin secretion from isolated rat glomeruli.

The sensitivity of renin release to changes in anion and calcium concentrations was assessed in superfused rat glomeruli with attached juxtaglomerular cells. Isosmotic substitution of Cl-with gluconate (1/12, 1/6, 1/3, 2/3, or total exchange), isethionate (15 or 101 mM), or sulfate (10 mM) inhibited renin release reversibly. Substitution of Cl- with nitrate (101 mM) stimulated renin secretion. Substitution with iodide (15 or 101 mM) had no consistent effect. The stimulation induced by calcium-free solutions was high in May and low in September. In the absence of chloride, the response to calcium-free solution was inhibited similarly all year. In May reintroduction of calcium and chloride stimulated renin release, suggesting that releasable renin had been stockpiled during the exposure to calcium-free solution. In September reintroduction of calcium and chloride inhibited renin release. It is concluded that the renin secretory process has a demand for permeant anions. The stimulation caused by low external calcium involves at least two mechanisms: one is anion sensitive, powerful, varies with the season, and includes a recruitment phenomenon; another is anion insensitive and weak.

Animals↗
PubMed1994

Differential effects of extracellular anions on renin secretion from isolated perfused rat kidneys.

We investigated the relevance of anions for the regulation of renin secretion from the kidneys. For this purpose we measured renin release from isolated rat kidneys that were perfused with medium containing either 120 mmol/l (normal) chloride or 95 mmol/l of isethionate, acetate, or nitrate anions in exchange for equimolar amounts of chloride. Lowering the extracellular chloride concentration by either of these maneuvers significantly enhanced renin secretion rates (RSR) at a perfusion pressure of 100 mmHg. Increasing pressure above 100 mmHg inhibited renin release in the presence of isethionate and acetate but not with nitrate anions. The renin stimulatory effects of isethionate and acetate but not that of nitrate anions disappeared in the presence of bumetanide (100 mumol/l), an inhibitor of macula densa chloride transport. Activation of renin secretion by isethionate and acetate was blunted with 100 pmol/l angiotensin II (ANG II), whereas tenfold higher concentrations of ANG II were required to attenuate the effect of nitrate ions. The amount of renin released in the presence of nitrate was fully additive to RSR values obtained with maximally effective doses of isoproterenol. These findings are consistent with the idea that impermeant anions such as isethionate and acetate enhance renin secretion from the kidneys predominantly via the tubular macula densa mechanism. The stimulatory influence of membrane-permeable nitrate anions appears to involve additional pathways and is mediated by a decreased calcium sensitivity of the renin secretory process rather than resulting from an adenosine 3',5'-cyclic monophosphate-dependent action.

Acetates↗
PubMed1997

Ion currents and mechanisms of modulation in the radula opener muscles of Aplysia.

Ion currents and mechanisms of modulation in the radula opener muscles of Aplysia. J. Neurophysiol. 78: 2372-2387, 1997. Numerous studies of plasticity in the feeding behavior of Aplysia have shown that substantial plasticity is due to peripheral neuromodulation of the feeding musculature. Extensive previous work focusing on the accessory radula closer (ARC) muscle has led to the realization that a major function of the modulation in that muscle may be to ensure efficient coordination between its contractions and those of its antagonist muscles. For a more complete understanding, therefore, we must study these muscles also. Here we have studied the radula opener muscles I7-I10. Using single isolated muscle fibers under voltage clamp, we have characterized ion currents gated by voltage and by the physiological contraction-inducing neurotransmitter acetylcholine (ACh) and the effects of the physiological modulators serotonin, myomodulins A and B, and FMRFamide. Our results explain significant aspects of the electrophysiological behavior of the whole opener muscles, as well as why the opener and ARC muscles behave similarly in many ways yet differently in some key respects. Opener muscles express four types of K currents: inward rectifier, A-type [IK(A)], delayed rectifier [IK(V)], and Ca2+-activated [IK(Ca)]. They also express an L-type Ca current [ICa] and a leakage current. ACh activates a positive-reversing cationic current [IACh(cat)] and a negative-reversing Cl current [IACh(Cl)]. The opener muscles differ from the ARC in that, in the openers, activation of IK(A) occurs approximately 9 mV more positive and there is much less IACh(Cl). In both muscles, IACh(cat) most likely serves to depolarize the muscle until ICa activates to supply Ca2+ for contraction, but further depolarization and spiking is opposed by coactivation of IK(A), IK(V), IK(Ca), and IACh(Cl). Thus the differences in IK(A) and IACh(Cl) may well be key factors that prevent spikes in the ARC but often allow them in the opener muscles. As in the ARC, the modulators enhance ICa and so potentiate contractions. They also activate a modulator-specific K current, which causes hyperpolarization and depression of contractions. Finally, in the opener muscles but not in the ARC, the modulators activate a depolarizing cationic current that may help phase-advance the contractions. Each modulator exerts these effects to different degrees and thus has a distinct effect on voltage and contraction size and shape. The overall effect then will depend on the specific combinations of modulators released in different behaviors. By understanding the modulation in the opener muscles, as well as in the ARC, we are now in a position to understand how the behavior of the two muscles is coordinated under a variety of circumstances.

4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone↗
PubMed1986

Effect of bovine heart atrial natriuretic and diuretic fractions on sodium transport in isolated toad skin.

The effects of two bovine heart atrial fractions (AF I and AF II) were investigated in toad skin. When added to the inner (serosal) solution, AF I caused a maximal reversible depression of the transepithelial potential and short-circuit current of about 60% and AF II induced maximal decline of these parameters of only 35%. When added to the outer (mucosal) solution, the effect of both fractions was often only partially reversible. Isaacson's amiloride test showed that AF I decreased the numerical estimates of all the components in the electrical equivalent circuit. The net Na+ flux decreased due to a fall in Na+ flux in the active direction. Incubation with Ca2+-free Ringer's solution decreased and Ca2+ ionophore A 23187 increased the effect of AF II. Partial replacement of sodium by choline in the outer solution slightly reduced the effect and substitution of normal Ringer's solution with sulfate or isethionate Ringer's solution in the outer solution significantly enhanced the effect of the AF. These results indicate that bovine heart atrial natriuretic fractions decrease the sodium potential (ENa), sodium conductance (GNa) and passive conductance (Gsh). The fall in net Na+ transport measured with sodium tracer fluxes confirms the decrease in ENa and GNa.

Amiloride↗
PubMed1984

Effect of alanine transport on ionic fluxes across the cell membrane in rat liver.

Changes in cell volume and alanine, Na+ and K+ concentrations and fluxes were studied in rat isolated hepatocytes or perfused liver. Addition of 10 mM alanine elicited a noticeable entry of Na+ which accumulated into the cells, along with a leakage of cell K+. Concurrently, the cell volume was 13% increased. These processes were also present with perfused livers in which alanine uptake, Na+ entry and cell swelling were proportional to the induction of the A system. K+ efflux was parallel to cell swelling and occurred very early after exposure of liver cells to alanine (and was transitory). The rôle of extracellular anions was investigated: alanine transport was not affected by replacement of Cl- and HCO-3 by a permeant anion whereas it was inhibited with the non-permeant anion isethionate. The present results indicate that the disturbances of the ionic gradients consecutive to alanine transport in isolated hepatocytes also operate in the liver organ itself. The possible implications of these phenomenons are discussed.

Alanine↗
PubMed1975

[Inhibitory effect of taurine on ouabain-induced arrythmia].

Myocardial taurine level was found to be greater in the rat than in the guinea-pig. Taurine inhibited the development of arrhythmias caused by the i.v. infusion of ouabain in the rat. When ouabain induced arrhythmias, the myocardial taurine level decreased. Both effects were blocked by pretreatment of propranolol. The uptake of taurine into the heart did not necessarily result in the reversal of the PR interval prolonged by ouabain. The protecting effect of taurine against ouabain toxicity was not dependent upon the change in myocardial total ATPase activity.

Adenosine Triphosphatases↗
PubMed1976

[Interaction of complex esters of hydroxyethylsulfones with DNA in vitro].

The effect of a number of alkyl disulphones on the parameters of DNA melting following its treatment with the substances involved was studied under in vitro conditions: it was found that bis(acetyl oxyethylsulphonyl) methane and bis (formyl oxyethylsulphonyl) methane reduced the temperature of DNA melting. As a result of decomposition of oxyethylsulphone esters the corresponding vinylsulphones were formed. It is suggested that the parameters of DNA melting change under the influence of vinylsulphones being formed. There is some correlation between antitumor activity of alkyl disulphones and their capacity to interact with DNA. Inactive or insignificantly active substances would not influence the parameters of DNA melting, while the two substances under consideration possessed a high antitumor effect on ascites forms of animal tumors.

Alkanesulfonates↗