碳酸氢盐和二氧化碳在跨内皮液体流动及角膜厚度控制中的作用。

The roles of bicarbonate and CO2 in transendothelial fluid movement and control of corneal thickness.

作者信息

Riley M V, Winkler B S, Czajkowski C A, Peters M I

机构信息

Eye Research Institute of Oakland University, Rochester, Michigan.

出版信息

Invest Ophthalmol Vis Sci. 1995 Jan;36(1):103-12.

PMID:7822137

Abstract

PURPOSE

To determine whether maintenance of corneal hydration is dependent on bicarbonate ions and whether these ions can be derived from metabolic or exogenous CO2, and to investigate the relationship of transendothelial fluid movement to control of hydration.

METHODS

The thickness of intact or deepithelialized rabbit corneas was measured while superfused on the endothelial surface with either 33 mM HGO3-/5% CO2 buffered media or 10 mM HPO4- buffered media in the presence and absence of inhibitors of ion transport and respiration. The corneal surface was covered with either silicone oil ("normal" corneas) or with the same media used for superfusion ("swollen" corneas). ATP and Na+,K(+)-ATPase activity were measured in endothelia scraped from the tissues after superfusion.

RESULTS

Intact and deepithelialized corneas covered with oil swelled at a negligible rate (4 to 8 microns/hour) in 33 mM HCO3- medium but at 45 to 60 microns/hour in HPO4- medium. Antimycin A altered neither of these swelling rates, but ethoxzolamide (0.1 mM) caused swelling in HCO3-/CO2 (approximately 12 microns/hour above controls) with no change of rate in HPO4-. Ouabain (0.1 mM) increased swelling to 45 to 50 microns/hour in HCO3-/CO2 but had no effect in HPO4-. Saturating the oil on deepithelialized corneas with 5% CO2, or putting HCO3-/CO2 medium on the epithelial surface of intact corneas, did not alter the swelling rates seen with HPO4- superfusion. The equilibrium thickness of deepithelialized corneas swollen with HCO3-/CO2 on both surfaces was 35 microns less than that of corneas swollen in HPO4-. The difference was abolished by ouabain, which caused corneas in HCO3-/CO2 to swell an additional 30 microns but did not alter the equilibrium thickness of corneas swollen in HPO4-. Ethoxzolamide and DIDS (0.2 mM) increased the thickness in HCO3-/CO2 but not in HPO4-. Na+,K(+)-ATPase activities of endothelia were similar after HCO3-/CO2 and HPO4- superfusions, but the concentration of ATP in the HPO4(-)-superfused tissues was increased 35%.

CONCLUSIONS

Normal corneal thickness can be maintained in vitro only in media that contain HCO3- at concentrations of more than 20 mM. Neither metabolic CO2 nor CO2 present in air-equilibrated, nominally HCO3(-)-free media can supply this requirement for HCO3-, even though these sources support the presumably related processes of transendothelial fluid movement and intracellular pH regulation.

摘要

目的

确定角膜水合作用的维持是否依赖于碳酸氢根离子，以及这些离子是否可来源于代谢产生的或外源性的二氧化碳，并研究跨内皮液体移动与水合作用控制之间的关系。

方法

在完整的或去上皮的兔角膜内皮表面用33 mM HCO₃⁻/5% CO₂缓冲介质或10 mM HPO₄²⁻缓冲介质进行灌流，同时存在和不存在离子转运及呼吸抑制剂，测量角膜厚度。角膜表面覆盖硅油（“正常”角膜）或用于灌流的相同介质（“肿胀”角膜）。灌流后，测量从组织刮下的内皮中的ATP和Na⁺,K⁺-ATP酶活性。

结果

覆盖硅油的完整和去上皮角膜在33 mM HCO₃⁻介质中以可忽略不计的速率（4至8微米/小时）肿胀，但在HPO₄²⁻介质中以45至60微米/小时的速率肿胀。抗霉素A未改变这两种肿胀速率，但乙氧唑胺（0.1 mM）在HCO₃⁻/CO₂中引起肿胀（比对照高约12微米/小时），而在HPO₄²⁻中肿胀速率无变化。哇巴因（0.1 mM）使HCO₃⁻/CO₂中的肿胀增加到45至50微米/小时，但在HPO₄²⁻中无作用。用5% CO₂使去上皮角膜上的硅油饱和，或在完整角膜的上皮表面放置HCO₃⁻/CO₂介质，均未改变HPO₄²⁻灌流时的肿胀速率。两面用HCO₃⁻/CO₂肿胀的去上皮角膜的平衡厚度比用HPO₄²⁻肿胀的角膜薄35微米。哇巴因消除了这种差异，它使HCO₃⁻/CO₂中的角膜再肿胀30微米，但未改变用HPO₄²⁻肿胀的角膜的平衡厚度。乙氧唑胺和DIDS（0.2 mM）使HCO₃⁻/CO₂中的角膜厚度增加，但在HPO₄²⁻中无此作用。HCO₃⁻/CO₂和HPO₄²⁻灌流后内皮中的Na⁺,K⁺-ATP酶活性相似，但HPO₄²⁻灌流组织中的ATP浓度增加了35%。