Nuclear Calcium Signaling in Retinal Pigment Epithelium

Abstract

Abstract: : Purpose: To describe the existence of intra-nuclear calcium release sites in retinal pigment epithelium. Methods: Confocal laser scanning microscopy was used to monitor intra-nuclear calcium dynamics in human RPE cells loaded with the calcium-sensitive dye Fluo-4. Forty-one cell nuclei were monitored after a cytoplasmic calcium wave was induced by mechanical stimulation of one of their neighbors. The calcium wave propagation speed was measured in the nucleus and cytoplasm of the cells adjacent to the stimulated one. Cross-correlation analysis was used to evaluate the exact time lag of the calcium wave propagation. Results: In resting RPE cells nuclear calcium fluorescence ([Ca²⁺]_n ) was relatively lower than the cytoplasmic levels. The perinuclear area usually showed higher calcium fluorescence. Mechanically induced cytoplasmic Ca²⁺ waves propagated to the nucleus. The rise in [Ca²⁺]_n was noted 0.1-0.3 msec after the cytoplasmic Ca²⁺ rise. The distribution of [Ca²⁺]_n was non-homogenous. We noted on average 4.3±1.3 (mean±SD) (range 2-7) intra-nuclear centers of [Ca²⁺]_n release. Conclusions: Cytoplasmic Ca²⁺ waves can induce [Ca²⁺]_n rise. Those intra-nuclear Ca²⁺ signals are non-homogenous and several activation centers can exist inside one nucleus. Since these centers are not near the nuclear membrane they might suggest the existence of intra-nuclear calcium release sites. Those release sites might be the nuclear channels previously described.

Keywords: retinal pigment epithelium • calcium • signal transduction