Impedance of the amphibian lens.

Duncan, G.; Patmore, Leslie; Pynsent, P B

doi:10.1113/jphysiol.1981.sp013613

Cited by 27 publications

(26 citation statements)

References 17 publications

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“…Several electrical impedance studies have mapped cell-cell resistance within the lens tissue as a function of depth (Baldo and Mathias, 1992;Duncan et al, 1981). Such studies have failed to provide evidence for the appearance of a novel conductive pathway between cells in the lens core.…”

Section: Discussionmentioning

confidence: 99%

Development of a macromolecular diffusion pathway in the lens

Shestopalov

Bassnett

2003

Journal of Cell Science

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The mammalian lens consists of an aged core of quiescent cells enveloped by a layer of synthetically active cells. Abundant gap junctions within and between these cell populations ensure that the lens functions as an electrical syncytium and facilitates the exchange of small molecules between surface and core cells. In the present study, we utilized an in vivo mouse model to characterize the properties of an additional pathway, permeable to macromolecules, which co-exists with gap-junction-mediated communication in the lens core. The TgN(GFPU)5Nagy strain of mice carries a green fluorescent protein (GFP) transgene. In the lenses of hemizyous animals, GFP was expressed in a variegated fashion, allowing diffusion of GFP to be visualized directly. Early in development, GFP expression in scattered fiber cells resulted in a checkerboard fluorescence pattern in the lens. However, at E15 and later, the centrally located fiber cells became uniformly fluorescent. In the adult lens, a superficial layer of cells, approximately 100 μm thick, retained the original mosaic fluorescence pattern, but the remainder, and majority, of the tissue was uniformly fluorescent. We reasoned that at the border between the two distinct labeling patterns, a macromolecule-permeable intercellular pathway was established. To test this hypothesis, we microinjected 10 kDa fluorescent dextran into individual fiber cells and followed its diffusion by time-lapse microscopy. Injections at depths of >100 μm resulted in intercellular diffusion of dextran from injected cells. By contrast, when injections were made into superficial fiber cells, the injected cell invariably retained the dextran. Together, these data suggest that, in addition to being coupled by gap junctions, cells in the lens core are interconnected by a macromolecule-permeable pathway. At all ages examined, a significant proportion of the nucleated fiber cell population of the lens was located within this region of the lens.

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Section: Discussionmentioning

confidence: 99%

Development of a macromolecular diffusion pathway in the lens

Shestopalov

Bassnett

2003

Journal of Cell Science

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“…3B) and with an electrode separation of 0 95 mm, this resistance was 3 kQ. Duncan, Patmore & Pynsent (1981) proposed a three-time-constant model to fit their impedance data, the three time constants arising from the surface membranes, internal fibre cell membranes and the extracellular space. Jacob & Duncan (1981 b) further proposed that the surface membranes contained two parallel pathways, one a passive conductance (leak conductance) and the other an active channel (voltage-dependent potassium conductance).…”

Section: Discussionmentioning

confidence: 99%

Raised intracellular free calcium within the lens causes opacification and cellular uncoupling in the frog.

Jacob¹

1983

The Journal of Physiology

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SUMMARY1. Ion-sensitive micro-electrodes were used to measure the levels of intracellular free Ca2+ within the intact amphibian lens. The free [Ca2+] was found to constitute 0 4 % of the total lens calcium.2. The pCa measured at the anterior lens surface was found to be 6-59, while that at the posterior was 5 70. An 8-fold anterior/posterior Ca2+ gradient thus exists along the optical axis.3. The intracellular free Ca2+ could be manipulated by incubating the lens in high-Ca2+ or Ca2+-free EGTA Ringer solutions.4. Raising the intracellular free Ca2+ to 0-22 mm caused lens opacification and cellular uncoupling; the coupling ratio was reduced from 1 in control to 0-41 in high Ca2+

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“…A glass micropipette filled with 2 M KCl (1-6 M⍀) inserted into a cortical fiber via the posterior of the lens measured Vm with reference to a low-resistance electrode in the bath. Lens cells are electrically very well coupled (16), and thus Vm is a measure largely of the voltage across the plasma membrane of the outermost cells. Electrical measurements were recorded using a two-channel, highimpedance amplifier (Firbank Electronics, Norwich, UK) in conjunction with an analog-to-digital converter (Handyscope, TiePie Engineering, Leeuwarden, The Netherlands) for storage and analysis on computer.…”

Section: Methodsmentioning

confidence: 99%

N-acetylhistidine, a novel osmolyte in the lens of Atlantic salmon (Salmo salar L.)

Rhodes

Breck²,

Waagbø³

et al. 2010

American Journal of Physiology-Regulatory, Integrative and Comp

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-Volume homeostasis is essential for the preservation of lens transparency and this is of particular significance to anadromous fish species where migration from freshwater to seawater presents severe osmotic challenges. In Atlantic salmon (Salmo salar L.), aqueous humor (AH) osmolality is greater in fish acclimated to seawater compared with young freshwater fish, and levels of lens N-acetylhistidine (NAH) are much higher in seawater fish. Here we investigate NAH as an osmolyte in the lenses of salmon receiving diets either with or without histidine supplementation. In the histidine-supplemented diet (HD) histidine content was 14.2 g/kg, and in the control diet (CD) histidine content was 8.9 g/kg. A transient increase in AH osmolality of 20 mmol/kg was observed in fish transferred from freshwater to seawater. In a lens culture model, temporary decreases in volume and transparency were observed when lenses were exposed to hyperosmotic conditions. A positive linear relationship between extracellular osmolality and lens NAH content was also observed, whereas there was no change in lens histidine content. Hypoosmotic exposure stimulated [ 14 C]-histidine efflux by 9.2-and 2.6-fold in CD and HD lenses, respectively. NAH efflux, measured by HPLC, was stimulated by hypoosmotic exposure to a much greater extent in HD lenses. In vivo, lens NAH increased in response to elevated AH osmolality in HD but not CD fish. In conclusion, NAH has an important and novel role as a compatible osmolyte in salmon lens. Furthermore, it is the major osmolyte that balances increases in AH osmolality when fish move from freshwater to seawater. A deficiency in NAH would lead to a dysfunction of the normal osmoregulatory processes in the lens, and we propose that this would contribute to cataract formation in fish deficient in histidine. histidine PREVALENCE OF CATARACT IN farmed Atlantic salmon (Salmo salar L.) has increased in recent years (3) and this has been linked to the removal of a rich source of dietary histidine (blood meal) (7). Several recent studies have investigated the possible causes of cataract in farmed salmon (6, 9, 30), although the mechanisms involved remain to be elucidated.Osmotic stress has been shown to contribute to cataract formation in multiple species, including man (19). Efficient volume regulation is crucial for the maintenance of lens transparency and disruption to the tightly packed and highly ordered cells and proteins that make up the lens will cause a loss of lens transparency. In fish there are numerous examples where osmotic factors have been shown to play a role in cataract development (20), and the anadromous life cycle of the Atlantic salmon exposes the fish to particularly severe osmotic stress. The early part of salmon development is spent in freshwater as parr followed by transformation to smolts before entering the sea. Despite the physiological changes associated with parr-smolt transformation, a preadaption for life in seawater, reversible osmotic cataracts, are commonly described immediately aft...

show abstract

Impedance of the amphibian lens.

Cited by 27 publications

References 17 publications

Development of a macromolecular diffusion pathway in the lens

Development of a macromolecular diffusion pathway in the lens

Raised intracellular free calcium within the lens causes opacification and cellular uncoupling in the frog.

N-acetylhistidine, a novel osmolyte in the lens of Atlantic salmon (Salmo salar L.)

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