摘要:

In human cornea an anion sensitive ATPase is present. The highest specific activity was found in the endothelium, whereas the epithelium contained the highest total activity. The enzyme was stimulated by bicarbonate and sulfite and inhibited by thiocyanate. The majority of the enzyme was localized in the mitochondria but some activity was also detected in the plasma membranes. Atractyloside inhibited only the mitochondrial anion ATPase.

ISSN:0271-3683    

DOI:10.3109/02713688509025153

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

In the past five years we have studied the penetration of locally applied sulfonamides into the eye, with a view toward developing new topical carbonic anhydrase inhibitors for the treatment of glaucoma.The drugs varied by 400 fold in their permeability to the anterior chamber and 20, 000 fold in permeability to the posterior chamber. We report now on two particular findings related to drug structure:1) Transcorneal permeability of the ionic or dissociated form of the drug is relatively high dissociated some 1/4 that of the undissociated form.2) Depending on the structure, certain compounds are sequestered in the cornea (presumably the stroma) and form a release system into the anterior aqueous.

ISSN:0271-3683    

DOI:10.3109/02713688509025154

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

The techniques of patch voltage clamping and whole cell clamping have been applied to the lenses and corneas of several species of animals. Numerous ion channels have been found in the basal and apical membranes of lens epithelial cells, anterior and posterior surface lens fibers, apical membrane of corneal endothelial cells, and apical membrane of the second layer of corneal epithelial cells. No ion channels have been found in deep lens fiber membranes to date.There are 9–11 different kinds of potassium channels in ocular epithelial membranes, several different kinds of non-selective cation channels, and one non-selective channel with a large unit conductance. Sodium selective channels are seen only rarely while chloride selective channels have not been seen at all. Several channels have not yet been identified unequivocally.Using the gigohm seal technique, it is possible to show that the frog lens epithelial cell membrane is dominated by potassium channels. Also, a technique is described for using the reversal potential of a 25–30 pS non-selective cation channel to measure the resting voltage of epithelial cells without penetrating them.The results of lens ion channel localization studies are in only qualitative agreement with previous lens channel localization studies which used whole lens impedance and ion substitution techniques. Limitations of using the patch clamp for ion channel localization are presented.

ISSN:0271-3683    

DOI:10.3109/02713688509025155

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

Electro-chemical steady state in the lens depends on the transport properties of its various constituent cells. These transport properties, at a minimum, include the active transport of Na/K and the passive leak of Na, K and CI through membrane channels. The work of Kinsey and Reddy (1), first localized active Na/K transport to the anterior surface cell membranes. In this paper, we estimate that the pump current density is 2 to 4vamp/cm2of surface membrane, by measuring the change in intracellular voltage when the lens is exposed to 100 uM ouabain. Our impedance data suggest the passive leak of K is mostly across the membranes of surface cells, but whether these are anterior or posterior cells is not yet known. Membranes of the fiber cells throughout the volume of the lens appear to have channels that are selective for Na and CI but few K channels. A simple model of electro-chemical steady state is derived to relate localized transport properties to the resting voltages in the lens. The above described localization of properties predicts radially circulating currents at steady state and spatial gradients in the intracellular and extracellular voltages. These predictions are compared to our measurements of steady state voltages and we find good agreement.

ISSN:0271-3683    

DOI:10.3109/02713688509025156

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

The lens junction protein (MIP26), and its trypsin cleavage product (MIP21), isolated from calf fiber cells, are incorporated into liposomes and the permeability and gating of the resulting channels are studied spectrophotometrically by an osmotic swelling assay. Liposomes incorporated with either protein and loaded with Dextran T-10 swell when placed in isotonic or hypertonic KC1, sucrose or polyethyleneglycol (PEG), indicating the presence of channels permeable to molecules as large as MW 1500. In the absence of calmodulin (CaM), the permeability of either MIP26 or MIP21 channels is not altered by Ca++. On the contrary, MIP26-CaM channels reversibly close in the presence of Ca-H-(10−5M). Preliminary experiments show channel closure with lowered pH (5.5) as well. While MIP26-CaM channels close to all the permeants tested, MIP21-CaM channels close only partially with Ca++, becoming impermeable to large probes (PEG) while remaining permeable to sucrose and KC1. This indicates that the trypsin-cleaved C-terminal arm of MIP26 is the channel gate.Evidence from spectrophotofluorometry and circular dichroism spectroscopy indicates that activated CaM changes the conformation of isolated MIP26, suggesting that channel occlusion could result from a change in protein configuration.

ISSN:0271-3683    

DOI:10.3109/02713688509025157

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

Membrane response to the various temperatures as one of the external factors was investigated in the lenses of the poikilothermal animal and the homothermal animal. The rainbow trout lens was used as the poikilothermal material and the rat lens as the homothermal material.The rainbow trout lens maintainedIn vitroits transparency without the changes of cation balance at 0°C−25°C, while cold cataract developed in the rat lens under the same conditions. Na, K-ATPase activity was detected at 0°C in rainbow trout lens but it was not detected in the rat lens. Lactic acid in the rainbow trout lens was produced for 30 successive days at 0°C, while that in the rat lens was not produced.The cataract developed at 37°C in rainbow trout lens, which we called“warm cataract.”Warm cataract developed not only when the lens was incubatedin. vitrobut also when rainbow trout was kept in fresh water at 37°C.Significant differences were detected in components of membrane lipids in the rainbow trout lenses compared to bovine lenses as the mammalian lens. The cholesterol/phospholipid ratio in the trout lens membrane was lower than that in bovine lens. This suggests that a poikilothermal animal lens can maintain the membrane fluidity at low temperatures.These results might suggest that the membrane characteristics in the rainbow trout lens play a role to maintain its transparency at low temperatures.

ISSN:0271-3683    

DOI:10.3109/02713688509025158

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

The utility of Ca efflux studies to examine lens calcium balance is limited because of the dominant contribution of efflux from the extracellular space of the lens. On the other hand, examination of lens“Ca uptake characteristics can generate valuable information regarding the mechanism by which calcium is largely restricted from the intracellular compartment. Such studies have enabled us to demonstrate that the access of calcium to the intracellular compartment is dependent to some extent upon the concentration of calcium in the extracellular environment. Additionally, experimental evidence speaks against extracellular binding of calcium. Finally, lens membrane permeability to calcium appears to be independent of membrane voltage.

ISSN:0271-3683    

DOI:10.3109/02713688509025159

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

While calcium is possibly involved in cataractogenesis, it is unquestionably involved in normal lens physiology. Numerous reports have documented the many cellular processes in other tissues affected by alterations in cellular levels of calcium. The homeostasis of the lens is no less dependent on the critical balance of intracellular calcium. With advances being made in calcium-sensitive microelectrodes and pioneering studies progressing in ion channel electrophysiology, interest in calcium metabolism in the lens has been intensified. This report is an attempt to review recent findings that deal solely with biochemical changes resulting from calcium imbalances in the lens interior.

ISSN:0271-3683    

DOI:10.3109/02713688509025160

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

In the Isolated human lens, short circuit current was inhibited by pharmacological concentrations of 6-methylprednisolone and opacities occured in the posterior subcapsular region in some lenses. The effect was seen only when the anterior (epithelial) surface of the lens was exposed. There was an increase of the short circuit current in the rabbit lens by 6-methyl-prednisolone and the lenses remained clear. Methylprednisolone effects were seen in spite of Na-K-ATPase inhibition by ouabain. Aldosterone had no effect on the translenticular potential difference, short circuit current and transparency. The data are discussed with respect to corticosteroid receptors in the lens epithelium and to the pathogenesis of steroid-associated cataract in man.

ISSN:0271-3683    

DOI:10.3109/02713688509025161

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

Enzyme, electrolyte and fluid secretion from exocrine glands is stimulated by neurotransmitters and peptide hormones. Whereas for some of these secretagogues calcium is an important intracellular messenger, for others it is cyclic AMP. Regulation of steady state free Ca2+concentration at rest and at stimulation have been studied in isolated permeabilized acinar cells from pancreas, parotid and lacrimal glands by measuring the free Ca2+concentration ofthe surrounding incubation medium with a Ca2+-specific macroelectrode. Ca2+transport mechanisms have been further characterized in subcellular membrane fractions by measuring45Ca2+uptake into membrane vesicles from rough endoplasmic reticulum (RER) and plasma membranes (PM). The data show that the intracellular messenger for secretagogue-induced Ca2+release from RER is inositol-1, 4, 5-tris-phosphate (IP3) which is produced during stimulation by phospholipase C mediated hydrolysis of phosphatidylinositol-bisphos-phate. At rest both Ca2+uptake into RER and Ca2+extrusion from the cell is promoted by (Ca2++ Mg2+)-ATPases with different characteristics in both types of membranes and by a coupled Na+/Ca2+countertransport in the PM which keep cytosolic free Ca2+concentration at a low level of -2–4×10−7mol/1. During stimulation the Ca2+permeability of endoplasmic reticulum membrane increases via IP3and that of the PM by a yet unknown“receptor-operated”mechanism. These events lead to increase in cytosolic free Ca2+concentration that is a trigger for enzyme, electrolyte and fluid secretion.

ISSN:0271-3683    

DOI:10.3109/02713688509025162

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor