Best's disease, an early onset macula dystrophy, is caused by mutations in the VMD2 gene expressed in the retinal pigment epithelium (RPE). Aim of this study was to investigate the cell physiology of RPE cells of Vmd2-deficient and wild-type (wt) mice. RPE cells were isolated from murine eyes under Ca2+ -free conditions and held over night prior to measurement. Cl- membrane currents were measured under K+ free conditions using the patch-clamp technique. Freshly isolated RPE cells showed a Ca2+ -sensitive Cl- current, but no difference in membrane conductance between wt and Vmd2 deficient mice. Intracellular free calcium concentration ([Ca2+ ]i) was monitored using the Fura-2 Ca2+ imaging method. RPE primary culture and the RPE cell line ARPE-19 showed a similar pattern of ATP induced [Ca2+ +]i responses. An initial fast [Ca2+ ]i increase was followed by a slight transient decrease below resting [Ca2+ ]i before a sustained increase followed. Emptying intracellular Ca2+ stores by thapsigargin (1mM) reduced the initial [Ca 2+ ]i increase. RPE cells from Vmd2 deficient mice showed a faster and higher Ca2+ -response compared to RPE cells from wt mice. These results seem to support our hypothesis, that bestrophin, the product of the VMD2 gene, might be involved in the Ca 2+ homoeostasis of RPE cells.

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