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Age- and Disease-Related Changes of Calcium Channel–Mediated Currents in Human Müller Glial Cells

¹ From the Department of Neurophysiology, Paul Flechsig Institute of Brain Research, University of Leipzig, Leipzig, Germany; and the ² Department of Ophthalmology, Eye Hospital, University of Leipzig, Leipzig, Germany.

PURPOSE. To determine whether the expression of voltage-gated Ca²⁺ channels in human Müller glial cells changes during normal aging and in cells from patients with proliferative vitreoretinopathy (PVR).

METHODS. Müller cells were enzymatically isolated from retinas of healthy donors and from excised retinal pieces of patients with PVR, and the whole-cell, voltage-clamp technique was used to characterize the current densities of transient, low-voltage–activated calcium channels and of sustained, high-voltage–activated calcium channels, respectively. To obtain maximal currents through both channel types, Na⁺ ions were used as the charge carrier.

RESULTS. During normal aging, Müller cells developed a hypertrophy, as indicated by an increase of the cell membrane capacitance. The mean membrane capacitance of cells from aged donors ( 60 years old) was elevated by 25% compared with cells from younger donors. The hypertrophy was not accompanied by a changed density of low-voltage–activated currents, whereas the density of the high-voltage–activated currents was enhanced by 76%. The density of the high-voltage–activated currents increased in correlation with the increase of the cell membrane capacitance and with the age of the donors. In the case of PVR, Müller cells displayed a strong hypertrophy accompanied by a downregulation of both current types by approximately 65%.

CONCLUSIONS. Both normal aging and PVR cause a gliotic reactivity of human Müller cells, as indicated by their hypertrophy. The type of reactivity, however, differs between the two conditions. Normal aging is accompanied by an increased expression of voltage-gated Ca²⁺ channels, whereas in PVR Ca²⁺ channel expression is decreased.

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