PubMed Health⌕ Search

Biomedical subjects

D Erlij

Publications and source records attributed to D Erlij.

At least 55 records · Page 3Linked to original sources
PubMed1980

Intracellular voltage of isolated epithelia of frog skin: apical and basolateral cell punctures.

Isolated epithelia of frog skin were prepared with collagenase, and the cells were punctured with intracellular microelectrodes across their apical (outer) and basolateral (inner) surfaces. Regardless of the route of cell puncture, the intracellular voltage (Vosc) in short-circuited isolated epithelia was markedly negative, averaging -70.4 mV for apical punctures and -91.6 mV for basolateral punctures. As in intact epithelia, amiloride outside caused the Vosc to become more negative (means of -96.7 and -101.8 mV), with a concomitant increase in the resistance of the apical barrier. Increasing the [K)i of the basolateral solution from 2.4 to 8.0 or 14.4 mM caused rapid step depolarization (5-10 s) of the Vosc under transepithelial Na transporting and amiloride-inhibited conditions of Na transport, with the delta Vosc ranging between 23.9 and 68.3 mV per decade change of [K]i. The finding that the Vosc of isolated epithelia of frog skin is independent of the route of cell penetration is consistent with the notion that the cells of the stratified epithelium are electrically coupled (functional syncitium). Moreover, the isolated epithelium can serve as a useful preparation, especially in studies designed to investigate the properties of the basolateral surfaces of cells.

Animals↗
PubMed1978

Nonhormonal mechanisms for the regulation of transepithelial sodium transport: the roles of surface potential and cell calcium.

An attempt to define the main categories of regulatory mechanisms of transepithelial sodium transport across tight epithelia is presented. In particular, evidence suggesting two types of mechanisms, changes in surface potential and the level of cell Ca, are described in greater detail. We have measured the effects of conditions that affect surface potential on the transepithelial sodium transport. Those conditions that increase the screening of negative charge and therefore depolarize the outer membrane are expected to have effects homologous to a depolarization caused by external current. Indeed, when the composition of the outside solution was modified by (i) increasing ionic strength, (ii) adding polyvalent cations (La+++, Co++, Ni++, Cd++), or (iii) lowering pH, an increase in active Na transport was detected. Moreover, the presence of small concentrations of polyvalent cations which screen surface charge, markedly dampens or even eliminates the effects of pH or ionic strength on Na transport. These findings provide additional support for the notion that a potential-sensitive component regulates Na movements across the apical membrane of the frog skin, and offer a framework to understand the effects of numerous cationic agents on transepithelial transport that hitherto remain unexplained. With respect to the role of intracellular Ca we have found that procedures that increase cell Ca, like removal of sodium in the basal solution or addition of ionophore A23187, reduce transepithelial Na transport. Moreover, conditions that block the increase in cell Ca prevent the inhibition of transport. These observations suggest that the level of intracellular Ca may determine the rate of transepithelial Na transport.

Animals↗
PubMed1977

Differences between resting and insulin-stimulated amino acid transport in frog skeletal muscle.

We have compared some features of the resting and the insulin-stimulated uptake of alpha-aminoisobutyrate (AIB) in frog skeletal muscle. We found a substantial difference between the two processes, namely, that resting AIB uptake is Na-independent while the insulin-stimulated fraction of the AIB uptake is Na-dependent. Since the amino acid transport systems in frog skeletal muscle are poorly characterized, we have also surveyed some of their properties. One of the most interesting findings of this survey is that both the uptake and efflux of AIB are inhibited by low concentrations of PCMBS (parachloro-mercury-benzene sulfonic acid 5 X 10(-5) M). In contrast, the carrier mediated transport of basic amino acids is neither inhibited by this mercurial agent nor accelerated by insulin. The action of PCMBS strongly suggests the presence of a critical sulfhydryl group in the amino acid carrier system utilized by AIB. This group is exposed to the outside solution since PCMBS penetrates cell membranes poorly, and in addition its inhibitory actions were reverted by agents that do not penetrate the cell membrane like albumin or glutathione.

4-Chloromercuribenzenesulfonate↗
PubMed1976

Action of insulin and cell calcium: effect of ionophore A23187.

We have measured the effects of the carboxylic Ca++ ionophore A23187 on muscle tension, resting potential and 3-O-methylglucose efflux. The ionophore produces an increase in tension that is dependent on external Ca++ concentration since (a) the contracture was blocked by removing external Ca++ and (b) its size was increased by raising outside Ca++. Neither resting potential nor resting and insulin-stimulated sugar efflux were modified by the ionophore. These data imply that the action of insulin is not mediated by increasing cytoplasmic [Ca++]. Additional support for this conclusion was obtained by testing the effects of caffeine on sugar efflux. This agent, which releases Ca++ from the reticulum, did not increase resting sugar efflux and inhibited the insulin-stimulated efflux. Incubation in solutions containing butyrated derivatives of cyclic AMP or cyclic GMP plus theophylline did not modify the effects of insulin on sugar efflux. Evidence suggesting that our experimental conditions increased the cytoplasmic cyclic AMP activity was obtained.

Animals↗
PubMed1976

Different effects of calcium flux-blocking agents on light and potassium stimulated release of taurine from retina.

Conditions for the stimulation of taurine release by illumination or increased K+ concentrations were established. The effect of Mg2+, ruthenium red and verapamil on taurine release induced by both procedures was compared. All these agents antagonize Ca2+-dependent release of neurotransmitters. Illumination-induced release of taurine was not blocked by any of these agents while the K+-induced release was blocked by all of them. It is discussed whether illumination and potassium act through processes that increase Ca2+ influx through different mechanisms, or if illumination-induced release is a Ca2+-independent process.

Animals↗
PubMed1976

Basic electrical properties of tight epithelia determined with a simple method.

A simple method for the routine mounting of epithelia which greatly reduces or eliminates faulty sealing at the edge is described. The values of potential and resistance observed in the frog skin and toad urinary bladder are comparable to those found with more complicated methods designed to minimize edge damage. In agreement with observations in other epithelia, a direct relationship between short circuit and conductance is observed for frog skin and toad urinary bladder, implying that the relationship is a general feature of tight epithelia. Furthermore, the high values of transepithelial resistance imply that the lower limit for the paracellular shunt pathway resistance should be reset upwards.

Amiloride↗
PubMed1976

The number of sodium ion pumping sites in skeletal muscle and its modification by insulin.

1. [3H]ouabain binding by frog sartorius muscles shows at least two components: one linked to inhibition of the pump and another not related to transport inhibition. This is suggested by the finding that [3H]ouabain uptake continued to increase when (a) the glycoside concentration was increased beyond that causing maximum transport inhibition, and (b) exposure times longer than those required to produce full inhibition were used. 2. A number of 1600 pumping sites per mum2 of membrane was estimated considering only the cylindrical surface of the muscle. 3. Insulin stimulated the ouabain-sensitive components of 22Na efflux and 134Cs influx. It also increased [3H]ouabain binding to a level of 1-7 times the total resting value. The increases in [3H]ouabain binding and in 22Na efflux followed a similar relationship with respect to insulin concentration. 4. Insulin stimulated the Na pump in muscles whose pumping sites had been inhibited by ouabain and then transferred to a glycoside-free solution. This stimulation was observed before detecting any recovery of the initial pumping activity. 5. When both the resting and the insulin-stimulated 22Na efflux had been blocked by ouabain, an additional dose of insulin, in a ouabain-free solution, had no further effects on 22Na efflux. 6. The effects of insulin were unaffected by cycloheximide or by high concentrations of butyryl derivatives of cyclic AMP and cyclic GMP. 7. We conclude that there are two pools of Na pumping sites in muscle cells: one active and another inactive. Insulin unmasks the inactive pumping sites by a mechanism that is independent of protein synthesis, increases in intracellular [Na] or decreases in intracellular [K].

Adenosine Triphosphatases↗
PubMed1976

Stimulation of the sodium pump by azide and high internal sodium: changes in the number of pumping sites and turnover rate.

1. The effects of 5 mM azide on [3H]ouabain uptake and 22Na efflux were determined. Both glycoside uptake and 22Na efflux were enhanced by azide. 2. Azide stimulated the Na pump in muscles whose pumping sites had been inhibited by ouabain and then transferred to a glycoside-free solution. This stimulation was observed before detecting any recovery of the initial pumping activity. 3. When both the resting and the azide-stimulated 22Na efflux had been blocked by ouabain, an additional exposure to azide, in a ouabain-free solution, had no further effects on 22Na efflux. 4. It is concluded that the increase in Na pumping caused by azide is due in part to an increase in the number of pumping sites. 5. [3H]ouabain binding was measured in muscles with different intracellular alkali cation concentrations. Variations in [Na]i from 15 up to 50 mM did not significantly affect the amount of glycoside bound. A substantial increase in binding occurred when [Na]i reached 70 mM. 6. It is proposed that the increase in Na extrusion that occurs during the recovery of Na loaded muscles mostly results from an increased turnover rate of the pump rather than from an increase in number of pumping sites.

Animals↗
PubMed1975

Some features of hydrogen (ion) secretion by the frog skin.

We have studied the movements of H+ from the in vitro frog skin into the outside solution because it has been suggested that the movement of sodium from the outside solution into the skin may result from the forced exchange of Na+ by H+. Our main observations can be summarized as follows: (a) Hydrogen moves from the skin into the outside solution at a rate of 0.04 muequiv-cm-2-h-1 while Na+ influx had a value of 0.49 muequiv-cm-2-h-1. (b) The rate of H+ secretion is not significantly affected by substituting the Na+ in the outside solution by K+ nor by inhibiting Na+ influx with amiloride (5-10(-5) M). (c) Acetazolamide (5-10(-3) M) blocked H+ secretion without altering the potential difference across the skin. (d) The rate of H+ production is not underestimated because it may have been neutralized by HCO3- secreted into the outside solution in exchange for Cl-. Substituting all the Cl- by SO4(2-) in the outside solutions does not result in an increase in the rate of H+ production. (e) The steady-state rate of H+ secretion is not affected by large changes in electrochemical potential gradients for H+. Neither abolishing the potential difference across the skin nor a 10-fold change in H+ concentration in the outside solution affected significantly the steady-state rate of H+ secretion. (f) The H+ secretion was abolished by the metabolic inhibitors dinitrophenol (1-10(-4) M) and Antimycin A (1.5-10(-6) M) which also markedly reduced the potential difference across the skin. Observations (a), (b), and (c) suggest that H+ and Na+ movements across the outer border of the isolated frog skin are not coupled. The ratio of Na+ to H+ movements is very different from unity and Na+ movements can be abolished without any effects on H+ secretion and conversely H+ movements can be abolished without interruption of Na+ uptake. A second conclusion suggested by these results is that the H+ secretion does not result from movement of H+ following its electrochemical potential gradient since that rate of secretion is not affected by marked changes in either potential or [H+]. Furthermore, the effects of metabolic inhibitors suggest that H+ secretion requires the expenditure of energy by the cell.

Acetazolamide↗
PubMed1975

Structure of tight junctions in epithelia with different permeability.

Freeze-fracture studies have shown a network of intramembrane fibrils in the tight junctions of epithelia. A direct correlation between the number of fibrils and junctional permeability has been suggested by previous studies. However, we have made two groups of observations showing that junctional permeability is not univocally related to the complexity of the network revealed by freeze-fracture. (i) The tight junctions of the rabbit ileum mucosa are permeable to lanthanum, although they have a complex network of fibrils resembling the junctions of toad urinary bladder, which are impermeable to lanthanum. (ii) The tight junctions of the toad urinary bladder are normally of low permeability; however, when the luminal solution is made hypertonic with lysine, junctional permeability markedly increases and lanthanum permeates through the tight junctions. In freeze-fracture replicas, no differences between the fibrils of control and lysine-treated bladders were found. Our results indicate that junctional permeability is controlled not only by the complexity of the fibrilar network, but that some features of the junctions or the fibrils themselves, not yet revealed by electron microscopy, play a central role in regulating epithelial permeability.

Animals↗