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PubMed1994

Mutagenesis in mammalian cells can be modulated by radiation-induced voltage-dependent potassium channels.

In mammalian cells, little is known about the initial events whose ultimate consequence is mutagenesis or DNA repair. The role the plasma membrane may play as an initiator of such a pathway is not understood. We show, for the first time, that membrane voltage-dependent potassium (K+) currents, activated by ionizing radiation (Kuo et al., 1993), play a significant role in radiation mutagenesis. Specifically, we show that the frequency of mutation at the HGPRT locus is increased as expected to 37.6 +/- 4.0 mutations per 100,000 survivors by 800 cGy of ionizing radiation from a spontaneous frequency of 1.5 +/- 1.5. This increase, however, is abolished if either K+ channel blocker, CsCl or BaCl2, is present for 2 h following irradiation of the cells. RbCl, chemically similar to CsCl but known not to block K+ channels, is ineffective in reducing the mutation frequency. Treatment of cells with CsCl or BaCl2 had no effect on radiation-induced cell killing.

Animals↗
PubMed1990

Inhibition of mucin secretion in a colonic adenocarcinoma cell line by DIDS and potassium channel blockers.

The factors which influence the exocytosis of mucins are not well characterized. Since the physical properties of mucins may be affected significantly by the co-secretion of electrolytes and water, we studied the relationship between ion movement and mucin secretion in T84 cells, a human colonic adenocarcinoma cell line which has been well characterized with respect to apical chloride secretion. Secretion of mucin was assessed by immunoassay of mucin appearing in the medium within 30 min of stimulation. Cells were grown on plastic in DMEM/Ham's F12 medium and experiments were carried out at 70% confluence. Mucin secretion was stimulated by the calcium ionophore A23187, or A23187 plus vasoactive intestinal polypeptide. Stimulated mucin secretion was not affected by loop diuretics (furosemide (1 x 10(-3) M) or bumetanide (1 x 10(-4) M)), with or without the addition of ouabain (5 x 10(-5) M) and amiloride (1 x 10(-5) M), making it unlikely that transcellular chloride movements in necessary for mucin secretion. However, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; (1 x 10(-5) and 5 x 10(-5) M) and three potassium channel blockers BaCl2 (1 x 10(-3) and 5 x 10(-3) M), tetraethylammonium chloride (1 x 10(-2) M) and quinine (5 x 10(-4) M) inhibited mucin secretion. A DIDS-sensitive chloride channel or chloride/bicarbonate exchanger and a Ca2(+)-dependent potassium channel may play important roles in mucin secretion. Since plasma membranes are sparingly permeable to DIDS, the DIDS-sensitive site is likely to be on the apical plasma membrane, perhaps at an initiation locus for exocytosis.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1992

Subchronic toxicity of barium chloride dihydrate administered to rats and mice in the drinking water.

Barium Chloride dihydrate (BaCl2.2H2O) was given for 92 days to B6C3F1 mice and Fischer 344/N rats in their drinking water at levels of 0, 125, 500, 1000, 2000, and 4000 ppm. The no-effect level for this study was 2000 ppm BaCl2.2H2O in the drinking water. At 4000 ppm, daily consumption for mice was 436 to 562 mg/kg barium, up to four times more chemical than rats. Mortality ranged from 60 to 70% in mice and from 10 to 30% in rats in the 4000 ppm groups. Deaths in mice were associated with a treatment-related renal toxicity. Renal lesions in rats were much less severe than in mice and did not contribute to the treatment-related deaths seen in the high dose group. Body weights of both species and sexes in the 4000 ppm groups were lower than controls at 92 days. Male and female rats in treated groups exhibited higher serum phosphorus than controls. Serum sodium, potassium, and calcium levels in rats were unchanged by barium treatment, as were hematological values. In both species at 4000 ppm, motor activity, grip strength, and thermal sensitivity were marginally affected. These effects were probably secondary changes resulting from BaCl2 toxicity observed at this dose level. In a mating trial, no anatomical effects on offspring of rats or mice were seen. Rats receiving 4000 ppm exhibited marginal reductions in pup weights. No effects were seen on reproductive indices.

Animals↗
PubMed1987

Ion transport and cadmium-induced inhibition of ciliary activity and induction of swelling of epithelial cells in mouse trachea organ culture.

Swelling of epithelial cells and reduction of ciliary activity in mouse trachea organ culture occurred after incubation for 4 h with a rather low concentration of cadmium acetate (10 microM). Specific inhibitors of ion transport (Na+, K+, Cl-) such as furosemide, amiloride and ouabain did not mimic, abolish or increase the toxic effects induced by cadmium acetate. Exposure to cadmium acetate had no significant effect on electrolyte uptake (22Na+ and 86Rb+). These results suggest that the swelling of epithelial cells induced by cadmium acetate is not due to an osmotic swelling from an accumulation of electrolytes. Ba2+, known to have several biological properties in common with Ca2+, and to influence basolateral K+ flux, counteracted the toxic effects of cadmium acetate, whereas a more rapid and extensive swelling occurred with cadmium acetate in a medium without Ca2+. No effect on the uptake of 109Cd2+ was found with barium chloride, whereas in a medium without Ca2+ the Cd2+ uptake increased by 47%. Trifluoperazine (100 microM), a drug which in vitro binds tightly to calmodulin, imitated the toxic effects of 10 microM cadmium acetate. The combination of 10 microM cadmium acetate and 100 microM trifluoperazine resulted in an additive toxic effect. A possible mechanism for the cadmium acetate-induced swelling and inhibition of ciliary activity could, thus, be a disturbance of the regulatory activity of calmodulin.

Acetates↗
PubMedDate not supplied

Ion transport across the isolated intestinal mucosa of Anguilla anguilla (Pisces).

The posterior intestine of freshwater-adapted Anguilla anguilla has a serosa negative transepithelial potential difference (TPD), and a current corresponding to the flow of negative current towards serosa. The TPD and the short-circuit current (SCC) were inhibited by Na+ and K+ withdrawal, and Cl- substitution or BA2+ addition inverts TPD and SCC, suggesting a Cl- and Na+ current mucosa-serosa, a K(+)-Cl- cotransport and a K+ channel in the mucosal side. The TPD and SCC were inhibited by ouabain, DIDS, furosemide and amiloride, indicating the presence of a Na(+)-K(+)-ATPase, and Cl-/HCO3-,Na(+)-K(+)-Cl- and Na+/H+ cotransporters.

Anguilla↗
PubMed1987

Barium reverses the transretinal potassium gradient of the amphibian retina.

Barium chloride (Ba2+) was added to the bathing medium of the perfused retina-eyecup preparation of the tiger salamander. The electroretinogram (ERG) and intraretinal extracellular potassium activity ([K+]o) were analyzed using a double-barrel electrode, one of which was ion-selective for K+. The action of Ba2+ on the ERG was to attenuate the c-wave/slow PIII complex. In addition, Ba2+ dramatically decreased the [K+]o in the outer retina, enough to reverse the transretinal potassium gradient. These findings, together with the known properties of Müller cell K+ channels, form the basis of an explanation of why Ba2+ blocks slow PIII and not the b-wave of the ERG.

Animals↗
PubMed1985

Evidence for multiple sources of calcium involved on the contractile effects of agonists in the dog uterus. Influence of ovarian sexual hormones.

We compared the characteristics of Ca2+ pools involved in the contractile effect of acetylcholine (Ach), histamine (Hist), oxytocin (Oxy) and barium (Ba2+) in prepuberal untreated or estrogen plus progesterone dominated uteri. After Ca2+ (0.2 mM) withdrawal different rates of decay for cited agonists were observed. If Ca2+ concentration was increased to 2.0 mM before the Ca2+ withdrawal, the t 1/2 for Ach and Hist were markedly increased. Hormonal treatment significantly increase the rate of decay for all agonists except for Ba2+ independent of the initial Ca2+ concentration, suggesting that in this condition the tightly bound Ca2+ is absent.

Acetylcholine↗
PubMed1987

Some effects of cimetidine on the reproductive organs of rats.

The development of genital organs of rats chronically treated with cimetidine showed that the drug may present anti-androgenic activity. This treatment did not alter the sensitivity of vas deferens to noradrenaline, but increased their sensitivity to BaCl2. In the male reproductive system, cimetidine must have peripheral actions apart from the central ones observed after chronic treatment.

Animals↗
PubMed1988

Influence of steroid ovarian hormones and calcium on drug-induced contractions of the isolated immature uterine muscle of mouse. An analysis of histamine receptor system.

1. Through the relative responsiveness (rho) determined for histamine (Hist), oxytocin (Oxy) and acetylcholine (Ach) in prepuberal untreated, estrogen, and estrogen plus progesterone dominated uteri of mouse, it was possible to measure the capability of each receptor system, which mediates responses induced by these agonists. 2. In all cases values of rho for Hist were lower than those for Ach and Oxy independently of hormone treatment and calcium concentrations used (0.2 or 2.0 mM), suggesting that the ability of histamine receptor system to promote contraction of mouse uterus is less effective than those mediating responses induced by other agonists studied here. 3. A comparison between the present data with those previously reported for dog uterus showed marked differences in the abilities of the histamine receptor system to mediate histaminergic stimulus in myometrium of two different animal species. 4. The author suggests that genetic characteristics controlling the development of a given receptor system can play a role regulating physio-pharmacological actions of drugs in the myometrium.

Acetylcholine↗
PubMed1989

Do differences in innervation result in different post-synaptic responses to exogenous agonists?

1. The pharmacological reactivity of the epididymal and prostatic portions of the rat vas deferens to BaCl2, phenylephrine and carbachol were recorded by isometric and isotonic technique. 2. The maximum response induced by the three agonists were similar at the epidiymal end, while at the prostatic portion phenylephrine produced a response 80% lower than that of barium and carbachol. 3. The pD2 value to agonists and the sensitivity to calcium channel blockers were lower at the prostatic end. 4. The data suggest that not only the pharmacological reactivity of the prostatic and epididymal portions differs, but also that the activity of the prostatic portion is much more reduced to alpha 1-agonists.

Animals↗
PubMed1991

Antagonism of kinin-induced contraction of isolated rat uterus by the crude hydroalcoholic extract from Mandevilla illustris.

1. The crude aqueous/alcoholic extract (CE) of Mandevilla illustris (Apocynaceae) rhizomes was analysed against contractile response elicited by bradykinin (BK), lysyl-bradykinin (L-BK), oxytocin(Ot), acetylcholine (Ach), angiotensin II (AII) and barium chloride (BaCl2) in the isolated uterus of the rat. 2. The CE of this plant (0.5-2.0 mg/ml) caused a parallel and concentration-related rightward displacement of BK and L-BK contractile responses. Schild plot revealed a linear relationship (r close to one) and yielded nominal PA2 values of 3.6 and 3.2 respectively, but the slopes were significantly different from unity. 3. However, the anti-BK action of the CE of M. illustris was not selective to kinin action, since in the same range concentration the CE also affected uterine contractile responses induced by Ot, Ach, AII and BaCl2.

Acetylcholine↗
PubMed1991

Differential effects of various Ca2+ antagonists.

1. The effects of various Ca antagonists (nicardipine, nifedipine, verapamil, diltiazem, flunarizine, cinnarizine, lidoflazine and papaverine) were studied in one in vitro (inhibition of CaCl2 induced contractions in isolated rat aorta) and two in vivo tests [survival after BaCl2 in the rat and survival after arachidonic acid (AA) in the mouse]. 2. Test substances behave in different ways, thus suggesting varying mechanisms of action. 3. The three tests used are very simple and quick to perform, but taken together give a good preliminary information which allows classification of the products during the screening phase into four subgroups: dihydropyridines, verapamil, diltiazem and diphenylalkylamines.

Animals↗
PubMed1993

Effect of testosterone on the response of young rat vas deferens to norepinephrine.

1. Following in vitro treatment with 12 microM 6-hydroxy-dopamine, 2 microM B-oestradiol, 0.1 microM propranolol and 10 microM cocaine vasa deferentia isolated from young rats (21-23 days old) showed supersensitivity to norepinephrine (NE) compared to those from adult (3 months old) rats. 2. The pA2 values for prazosin were higher in young (9.6 +/- 0.1) than in adult (8.3 +/- 0.1) rat vas deferens, with the slopes of the Schild plots not different from 1.0 (0.78 +/- 0.26 and 1.14 +/- 0.14, respectively). 3. The treatment of young rats with a single dose of testosterone abolished the supersensitivity to NE and the higher affinity for prazosin. 4. We conclude that there is a reduction of neuronal NE uptake and a decrease in the sensitivity to NE in the vas deferens as the rat matures sexually. 5. Testosterone induces a decrease in the sensitivity to NE, probably via an action on the alpha 1-adrenoceptor population and the sympathetic nerve discharge in this organ.

Animals↗
PubMed1995

Effects of hypoxia, mechanical and chemical endothelium denudation on guinea-pig isolated pulmonary arteries.

1. The isolated unstimulated main trunk, extralobar and intralobar branches of the pulmonary artery of the guinea-pig developed well-sustained contractions upon exposure to hypoxia (95% N2-5% CO2 gas mixture; PO2 11-15 mm Hg). The contractions were readily reversible by reoxygenation (95% O2-5% CO2). 2. Mechanical removal of the endothelium did not significantly affect the magnitude of the hypoxia-induced contractions in rings obtained from the main trunk of the pulmonary artery but reduced those of rings obtained from the proximal and distal extralobar branches. 3. Mechanical removal of the endothelium also did not affect the magnitude of contractions induced by BaCl2 in the main but significantly reduced contractions induced by the same agent in the proximal and distal extralobar branches of the pulmonary artery, suggesting that the reduction of hypoxia-induced contractions in the endothelium-denuded rings is due to impairment of vascular reactivity. 4. Pretreatment with L-N-nitro arginine, an inhibitor of the synthesis of the endothelium-derived relaxing factor, did not significantly affect the hypoxia-induced contractions but increased the magnitude of BaCl2-induced contractions in the main and the extralobar branches. 5. These observations demonstrate that isolated pulmonary artery rings of the guinea-pig develop slow contractions in response to hypoxia without prior contraction with an agonist, and that the endothelium plays little role in the hypoxia-induced contractions of guinea-pig isolated large pulmonary arteries. 6. Furthermore, these observations suggest that the effect of mechanical endothelium denudation or pharmacological manipulation, such as EDRF inhibition, on vascular reactivity should be considered when the effect of hypoxia is studied in isolated pulmonary arteries.

Animals↗
PubMed1983

Response of cochlear potentials to presumed alterations of ionic conductance: endolymphatic perfusion of barium, valinomycin and nystatin.

Two models ('single-pump' and 'two-pump') of transepithelial potassium movement by the marginal cells of the stria vascularis have been proposed in the literature. Their validity was considered by exposing the endolymphatic (luminal) surface to agents (barium, valinomycin and nystatin) which are known to alter specific cellular membrane conductances in other tissues. This was accomplished by the use either of injections or of a relatively satisfactory technique for perfusion of scala media, which is described. Injection of barium caused the endocochlear potential (EP) to increase in normal animals and had no effect on the EP of deaf, Waltzing guinea pigs. Perfusion of the ionophores caused a decline in the EP in both normal and Waltzing guinea pigs. Only the 'two-pump' model (Na/K-ATPase-mediated cation pump on the basolateral membrane and rheogenic K transporter at the luminal membrane) is consistent with the results. The cellular heterogeneity of the cochlear duct, however, introduces a measure of uncertainty into this interpretation.

Animals↗
PubMed1985

Effects of barium and ion substitutions in artificial blood on endocochlear potential.

Previously, a qualitative assessment was made (Marcus, D.C. (1984): Am. J. Physiol. 247, C240-C246) of the ion-selective properties of the cells bounding the cochlear duct by observing the effects of ion substitutions in the perilymph on the transepithelial potential difference (endocochlear potential; EP). Contributions by the marginal cells of the stria vascularis to the observed changes in the EP may have been masked, however, due to their 'isolation' from the perilymph by a continuous layer of basal cells. Since the ionic milieu of the basolateral membranes of the marginal cells is controlled more directly by the blood supply than by the perilymph, we report here on the effects of ion substitutions via vascular perfusion. Elevated K (substituted for Na or N-methyl-D-glucamine; NMDG) or Ba caused marked depression of the EP. Decreased Na or Cl (replaced by NMDG and gluconate, respectively) also depressed the EP. These changes in the EP were distinctly different from those observed previously by perilymphatic perfusion, and were interpreted in terms of a modified model of the strial marginal cells.

Barium↗
PubMed1985

A drug used in traditional medicine: Harpagophytum procumbens DC. IV. Effects on some isolated muscle preparations.

Effects of the crude methanolic extract of Harpagophytum procumbens secondary roots and two of its active principles, harpagoside and harpagide, on some smooth muscle in vitro have been studied. The results obtained show how the action of H. procumbens is due to a complex interaction between the various active principles contained in the drug and suggest that they, especially harpagoside, interfere with the mechanisms that regulate the influx of calcium in the cells.

Acetylcholine↗
PubMed1991

Opioids activate both an inward rectifier and a novel voltage-gated potassium conductance in the hippocampal formation.

Opioid receptors were found to activate two different types of membrane potassium conductance in acutely dissociated neurons from the CA1/subiculum regions of the adult rat hippocampal formation. Opioid-responsive neurons were distinguished based on their morphology and electrophysiological responses. In one population of neurons having a multipolar, nonpyramidal cell shape, mu-selective opioid agonists increased an inward rectifying potassium current. Opioid activation of the inward rectifying conductance resulted in small outward potassium currents at resting membrane potentials and increased inward currents at hyperpolarized potentials. In a second population of nonpyramidal neurons, mu opioid agonists increased a novel voltage-gated potassium current. This current was blocked by internal CsCl2, unaffected by external BaCl2 or CdCl2, irreversibly activated by intracellular GTP-gamma-S, and inactivated by sustained depolarization. In contrast to the inward rectifying conductance, the voltage-gated conductance was not activated at resting membrane potentials or hyperpolarized potentials. The opioid-activated, voltage-gated conductance represents a new class of G protein-regulated potassium current in the brain.

Animals↗