Analysis of rat lens 45Ca2+ fluxes: Evidence for Na+Ca2+ exchange

doi:10.1016/0014-4835(91)90065-M

Experimental Eye Research

Volume 52, Issue 5, May 1991, Pages 619-627

https://doi.org/10.1016/0014-4835(91)90065-M Get rights and content

Abstract

The influx and efflux kinetics of ⁴⁵Ca²⁺ were studied in the rat lens in vitro. Both data sets could be fitted by a multi-compartment mathematical model and were interpreted in terms of extracellular, cytosolic and slowly-exchanging (bound) components. At the end of a 16-hr influx period, when uptake into the extracellular and cytosolic compartments is complete, the ⁴⁵Ca²⁺ exchanged fraction is less than 20% of the total calcium determined by atomic absorption. The bound compartment is therefore by far the largest in the lens.

The efflux rate constant determined from the model for the cytosolic compartment was approximately 8 × 10⁻³ min⁻¹ and its origin was confirmed by its sensitivity to temperature, absence of external sodium and presence of the amiloride-analogue, dichlorobenzamil. A 55% reduction in efflux was obtained in sodium-free solution, indicating that Na⁺Ca²⁺ exchange is responsible for a large proportion of calcium movement from the lens against its electrochemical gradient. This was confirmed in influx studies where, reduction of the lens sodium gradient by either exposure to sodium-free medium or 0·1 mm ouabain significantly elevated the ⁴⁵Ca²⁺ content of the lens relative to the control level.

Exposure to sodium-free conditions also rendered the lens opaque, which did not occur in the absence of external calcium. These experiments suggest a critical role for Na⁺Ca²⁺ exchange in maintaining a low internal Ca²⁺ and hence transparency.

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Analysis of rat lens 45Ca2+ fluxes: Evidence for Na+Ca2+ exchange

Abstract

Exp. Eye Res.

Exp. Eye Res.

Exp. Eye Res.

Exp. Eye Res.

Biophys. J.

Exp. Eye Res.

Exp. Eye Res.

Biochem. Biophys. Res. Commun.

Sodium-calcium exchange and smooth muscle function in non-vascular smooth muscles

The effect of sodium concentration on calcium movements in giant axon of Loligo forbesi

J. Physiol.

The influence of extracellular calcium binding on the calcium efflux from squid axon

J. Physiol.

Efflux of chloride from the rat lens: influence of membrane potential and intracellular acidification

Q. J. Exp. Physiol.

Membrane electrical properties of vesicular NaCa exchange inhibitors in single atrial myocytes

Circulation Res.

Studies on Na-K-ATPase. Correlation of enzyme activity with cation flux in six tissues

Arch. Biochem. Biophys.

Ca-ATPase activity in the rabbit and bovine lens

Invest. Ophthalmol. Vis. Sci.

Contribution of isotope flux studies to understanding the mechanism of the β-cell membrane

Analysis of rat lens ⁴⁵Ca²⁺ fluxes: Evidence for Na⁺Ca²⁺ exchange