ISSN:0271-3683    

DOI:10.3109/02713688509025143

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

Recent progress in studying epithelia in culture indicates that techniques already available and applied to naturally occurring epithelia can be applied effectively to cultured epithelia. Studies using this approach are summarized as well as new information the studies have yielded regarding the mechanism of action of aldosterone and the regulation of expression of the sodium-coupled hexose transporter. In addition, special features of cultured epithelia should lead to new approaches to understanding epithelial biology as well as epithelial transport.

ISSN:0271-3683    

DOI:10.3109/02713688509025144

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

The corneal epithelium of the rabbit is functionally characterized as a“tight”ion transporting cell layer. Its barrier properties arise from the high electrical resistance of both the outermost cell membranes and the paracellular zonulae occludens. The specific ion transport process and secondary fluid transport by this tissue are modulated via cyclic AMP. There is evidence for the autonomic control of CI”secretion by the corneal epithelium.

ISSN:0271-3683    

DOI:10.3109/02713688509025145

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

The stoichianetry of the Na-Cl ootransport mechanism at the base-lateral membrane of the frog corneal epithelium was studied with the aid of intracellular microelectrodes by analyzing the effects of ouabain on intracellular recordings (PDSC) and transepithelial short-circuit current (ISC). Under short-circuit conditions, the total current across the basolateral membrane was equated to the Cl−transport across the apical membrane. Ouabain produces a quick and steep decrease of PDSC(7.1 mV) and ISC(3.0μA/cm2) that was ascribed to a sudden inhibition of the electrogenic component of the Na-K pump. From these effects, and from results in previous studies, the maximum value for the Na+flux via the ootransport mechanism (ICNa) was estimated and compared to the apical Cl−transport (a minimum estimate of the Cl−flux cotransported with Na+). In all experiments, Iclwas larger than INa. Considering that Na+also recirculates across tne basolateral membrane via a passive pathway, the Cl:Na flux ratio of the ootransport system may be as high as 4.

ISSN:0271-3683    

DOI:10.3109/02713688509025146

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

The deepithelialized cornea is mounted in a chamber and perfused on both surfaces by identical closed systems. The technique allows the continuous measurement of the net water flux and the electrical potential across the preparation as well as the steady state flux of radioactive ions. The permeabilities of pairs of ions in the same direction were compared, and they were found to be closely proportional to their free diffusion constants, suggesting that they passed by way of the intercellular spaces. Technical difficulties prevented a valid determination of the existence of active ion transport, but there was no indication of its presence.

ISSN:0271-3683    

DOI:10.3109/02713688509025147

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

A model for endothelial transport is updated to include recent evidence. We discuss electrolyte movements based on a Na+-K+ATPase, a Na+-H+exchanger, a Na+-HCO3coupler, a Cl−-HCO3exchanger, a K+-C1−coupler, and K+and anion channels. We discuss near-isotonic transport of fluid on the basis of recent findings of high endothelial osmotic permeability.

ISSN:0271-3683    

DOI:10.3109/02713688509025148

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

Intracellular potential measurements of confluent monolayers of cultured bovine corneal endothelial cells were used to define passive ion transport processes in these cells. Previous studies (Jentsch et al. J. Membr. Biol. 78:103 (1984); Jentsch et al. J.Membr. Biol 81: 189 (1984)) have provided the experimental“Basis for a cellular model, in which bicarbonate entry across the basolateral membrane is indirectly driven by a Na+/H+-exchanger, which is inhibitable by amiloride (1mM). Bicarbonate and sodium should leave the cell via an electrogenic bicarbonate sodium cotransport, which is inhibitable by the disulfonic stilbene derivates SITS or DIDS. Tnis model is also consistent with results from transendothelial studies.In this paper, we briefly review the evidence we have obtained for this model and demonstrate, that the electrical response to sodium (depolarization upon Na -removal) is neither due to an inhibition of Na+/K -ATPase nor explainable in terms of changes in K -conductance. This is concluded from the observation of these responses in the presence of ouabain (10−4M) or barium (ImM).

ISSN:0271-3683    

DOI:10.3109/02713688509025149

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

Rabbit corneas were isolated, denuded of epithelium, and perfused on the anterior and posterior surfaces with Krebs Ringer-bicarbonate with additions of 50μM H2O2, 125μM BCNU, or 100μM ouabain. The permeability of the corneal endothelium to labelled mannitol and inulin was determined by adding these compounds to the endothelial perfusate and measuring the rate of appearance of radioactivity in the anterior perfusate. Both H2O2 and BCNU increased the flux of mannitol and inulin across the endothelium in a time dependent manner, but ouabain had no effect. Additions of glucose with H2O2 or of GSH with BCNU prevented the observed changes in permeability. ATPase activities in the endothelia of intact, isolated corneas were also determined following incubation in the same media. The only observable effects of H2O2 and BCNU were slight reductions in the activity of Na++K+ATPase. It is concluded that permeability changes, the leak, are more critical than active transport processes, the pump, in determining the rate and extent of swelling that results from exposure of the cornea to these agents.

ISSN:0271-3683    

DOI:10.3109/02713688509025150

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

Electron microprobe analysis was employed to measure the intracellular electrolyte concentrations of the bullfrog corneal epithelium. Under control conditions, transepithelial potential short-circuited and both sides of the isolated cornea incubated in Conway's solution, the mean intracellular concentrations were 8.0 for sodium, 18.4 for chloride and 117.3 for potassium (mmole/kg wet weight). These values are in good agreement with previously reported ion activities implying that the intracellular activity coefficient for small ions is close to that of the extracellular space. No significant differences between the nuclear and cytoplasmic concentrations of small diffusible ions were detectable. Similarly, the chloride concentrations in the different epithelial layers were virtually identical and showed parallel changes at varying states of chloride secretion, suggesting that corneal epithelium represents a functional syncytium. The behavior of the intracellular ion concentrations after removal of sodium, chloride or potassium from the outer or inner bath is consistent with a passive electrodiffusive efflux of chloride across the outer membrane and a sodium coupled chloride uptake across the inner membrane. Furthermore, effects of bicarbonate and CO on the rate of chloride secretion and on the intracellular sodium and chloride concentrations were observed, indicating a possible role of pH in regulating chloride secretion.

ISSN:0271-3683    

DOI:10.3109/02713688509025151

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

The messenger roles of cyclic AMP and the calcium ion in stimulus-secretion coupling are considered in the frog and bovine corneal epithelium, respectively. In the frog cornea, epinephrine stimulates net CI transport by increasing cyclic AMP content (1). This stimulation is associated with a larger apical membrane CI conductance and basolateral membrane ionic conductance (2). The response of the apical membrane conductance is thought to result from an increase in cyclic AMP content whereas the basolateral membrane ionic conductance increase is unrelated based on measurements of the effects of the calcium channel antagonist, diltiazem, and the beta agonist, isoproterenol, on the electrical parameters and cyclic AMP content. The basolateral membrane is essentially K permselective since the K channel blocker, Ba, depolarized the intracellular potential difference and increased the basolateral membrane resistance. Diltiazem had even larger effects on these parameters suggesting that this compound is a more effective inhibitor of K channel activity than barium. In broken cell preparations of bovine corneal epithelium, a high affinity form of Ca + Mg activated ATPase is present (Km=. 06μM for Ca) and is essentially of plasma membrane origin. This ATPase activation is at a Ca activity similar to the expected intracellular value and suggests that this activity is the enzymatic basis for net Ca transport.

ISSN:0271-3683    

DOI:10.3109/02713688509025152

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor