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Biomedical subjects

J Aceves

Publications and source records attributed to J Aceves.

71 records · Page 4Linked to original sources
PubMed1979

Estimation of the density of sodium entry sites in frog skin epithelium from the uptake of [3H]benzamil.

1. The inhibition of short circuit current in frog skin by benzamil (N-benzyl-amidino-3,5-diamino-6-chloropyrazine carboxamide) was investigated. When skins were bathed on both sides by Ringer solution (pH 7.6) the affinity was 5 x 10(7) M-1. When the sodium concentration was reduced to 1.1 mM and the pH adjusted to 6.5 the affinity increased to 8.5 x 10(8) M-1. 2. A method is described for measuring uptake of [3H]benzamil into the mucosal (outer) surface of pieces of isolated epithelium, 0.95 cm2 in area, under open circuit conditions. 3. The relation of [3H]benzamil uptake at the mucosal surface to its concentration was measured in solutions containing 1.1 mM-sodium and adjusted to pH 6.5. Uptake could be resolved into a linear component (10.2 f-mole nM-1) and a saturable component (21.5 f-mole cm-2) with a half saturating concentration of 1 nM. 4. In the presence of amiloride (1 microM) or unlabelled benzamil (1 microM) uptake was linear with concentration, and was, respectively, 9.2 f-mole nM-1 and 8.8 f-mole nM-1. When the pH was reduced to 3.5 uptake was again linear but reduced to 3.3 f-mole nM-1. 5. The identity of the saturable component of [3H]benzamil uptake to sodium entry sites is discussed. The results suggest a sodium entry site density of around 130 micron-2 of mucosal surface.

Amiloride↗
PubMed1979

Uptake of [3H]benzamil at different sodium concentrations. Inferences regarding the regulation of sodium permeability.

1. The effect of benzamil on short-circuit current in frog skin was measured at different external sodium concentrations. A linear relationship exists between the concentration of benzamil reducing short-circuit current by 50% and the external sodium concentration, indicative of some form of competitive antagonism between sodium and benzamil. 2. Uptake of [3H]benzamil into isolated frog skin epithelium and whole skin (0.95 cm2 pieces) was measured at different external sodium concentrations. With a sodium concentration of 111 mM in the external medium the uptake of [3H]benzamil is linear with concentration. Uptake amounted to 8.8 f-mole nM-1, a value similar to the linear component of the uptake measured at low (1.1 mM) sodium concentration. 3. Using a variety of other conditions the maximal number of specific binding sites for [3H]benzamil was calculated from displaceable binding and the fractional occupancy, the latter being derived from the inhibition of short-circuit current. This approach gave similar binding site densities to those reported previously at low sodium concentrations. 4. The reduction in specific [3H]benzamil uptake at high sodium may result from two mechanisms, competition of sodium with the ligand for an external binding site and a reduction in the site density as the intracellular sodium concentration increases. 5. It is concluded that the saturation of sodium transport which occurs at high sodium concentration is likely a consequence of the reduced availability of entry sites, rather than saturation of the uptake process.

Amiloride↗
PubMed1977

Pumped movements of sodium and potassium ions in the isolated epithelium of the frog skin.

The action of agents with well known effects on transepithelial Na transport was tested on Na extrusion in epithelial cells of the frog skin. The cells had been previously loaded with Na by incubation in cold, K-free solutions. DNP (5 X 10(-4)M) totally inhibited Na extrusion and K uptake, while amiloride (10(-5) M) did not show any effect on either of these processes. Ouabain (10(-6)M) and absence of K from the medium inhibited completely Na extrusion and K uptake without changing cell water content. Probably the most interesting finding is that K activated Na extrusion along a sigmoid curve, which suggests that, as in other cells, the Na pump of these epithelial cells has 2 sites for K activation. The half-activation concentration of the site with highest affinity was 0.27 mM, the other 1.3 mM. Na extrusion significantly exceeded K uptake either at low K in the medium or during initial recovery in normal K Ringer. This may indicate an electrogenic mode of pump activity.

Amiloride↗
PubMed1977

Sodium pump stimulation by oxytocin and cyclic AMP in the isolated epithelium of the frog skin.

Activity of the Na pump was judged by Na extrusion in epithelial cells loaded with Na by a previous incubation in K-free solutions in the cold. Oxytocin significantly stimulated Na extrusion either at normal (3.5 mM) or low (0.25 mM) K in the medium. It was stimulated as well by cyclic AMP. Maximal concentrations of either agent caused about the same degree of stimulation. Addition of ouabain or removal of K prevented the action of both agents, but amiloride showed no effect at all. These results strongly suggest that, a) neurohypophyseal hormones not only increase Na entry across the mucosal barrier of the epithelium but they also stimulate the serosal Na pump, b) cyclic AMP not only mediates the action of neurohypophyseal hormones on Na and water permeability of the mucosal barrier, but it also mediates the action of the hormones on the Na pump of the serosal barrier.

Animals↗
PubMed1973

The effect of amiloride on sodium and potassium fluxes in red cells.

1. The effect of amiloride on the influx and efflux of (24)Na and (42)K in red cells was studied. The drug was added to the bathing Ringer or else incorporated in resealed ghosts.2. Amiloride does not inhibit the active or the passive (ouabain insensitive) extrusion of (24)Na.3. Amiloride inhibits the influx of (24)Na into red cells by 70%.4. Whether added to the inside or to the outside of the cells amiloride has no effect on the efflux of (42)K.5. Amiloride does not modify the uptake of (42)K from control Ringer. This uptake is strongly inhibited by the removal of Na. Amiloride has no effect on the extent of this inhibition.6. It is concluded that amiloride specifically inhibits the passive penetration of Na, and has no effect on the Na-K-pumping mechanism. However, at the concentration which inhibits 70% of the influx, amiloride fails to produce an observable effect on the ouabain-insensitive Na-efflux.7. On the basis that the information obtained could be extrapolated to other membranes, the effect of amiloride on epithelial membranes is discussed.

Amiloride↗
PubMed1971

Sodium transport across the isolated epithelium of the frog skin.

1. A method to separate the epithelium from the underlying layers of the frog skin is described. The method is based on the combined use of collagenase and hydrostatic pressures.2. The potential difference and the short-circuit current values of isolated epithelia and whole skins are similar. Na net flux and short-circuit current are equivalent.3. The time course of changes in potential following rapid changes in composition of the bathing solutions shows that the barrier to K diffusion at the internal surface of the isolated epithelium is larger than the barrier to Na diffusion at the external surface.4. In the isolated epithelium there are 133 m-mole K(+) and 24.7 m-mole Na/l. cellular water. The amount of extracellular water was considered to be equal to the inulin space.5. Arginine vasopressin (0.1 u./ml.) markedly increased short-circuit current and potential difference in isolated epithelia. The amount of Na in the epithelium that equilibrated with Na in the external solution was not increased by the hormone.6. Ouabain (10(-4)M) reduced short circuit current and potential difference to values close to zero. The ouabain treated epithelia contained an increased amount of Na originating in the internal solution. On the other hand the amount of Na that originated from the external solution was not increased.7. The amount of epithelial Na that equilibrated with Na in the external solution was 0.009 mu-equiv/cm(2). This figure is about ten times smaller than the values found in whole skins.

Animals↗
PubMed1970

The mechanism of the paralysing action of tetramisole on Ascaris somatic muscle.

1. Tetramisole (100 mug/ml) paralysed live Ascaris in 3 min.2. Tetramisole (10 mug/ml) caused a sustained contraction of the isolated somatic muscles of the worm. This contraction was not blocked by curare nor by piperazine.3. Tetramisole reduced the resting potential of Ascaris muscle from 34+/-4 to 10+/-1 mV.4. Tetramisole caused contraction of Ascaris muscle previously depolarized with high K(+) solutions. This observation suggests that tetramisole can induce a contracture that is independent of membrane depolarization.

Acetylcholine↗