The Nuclear-Cytopiasmic [Ca 2+ ] Gradient in Single Mammalian Vascular Smooth Muscle Cells

Abstract

We studied the nuclear-cytoplasmic [Ca²⁺] gradient in single, freshly dispersed smooth muscle cells from the ferret portal vein, by means of fluorescence ratio imaging microscopy. Cells were loaded with the cell-permeant calcium indicator fura-2 AM. Caffeine and platelet-derived growth factor (PDGF) were used in order to mobilize Ca²⁺ from the sarcoplasmic reticulum. Basal levels of nuclear and cytoplasmic [Ca²⁺] were 299±51 nM and 141±23 nM respectively (n=10, p<0.001). At 3 min after lOmM caffeine, nuclear [Ca²⁺] decreased to 117±13 nM (n=10, p<0.001), cytoplasmic [Ca²⁺] also decreased to 75±11 nM (n«10, p<0.001) and the nuclear-cytoplasmic difference was no longer significant (p>0.05). Similarly, 300pM of PDGF also abolished the nuclear-cytoplasmic [Ca²⁺] gradient (n=12, p>0.1). We conclude that in single muscle cells from the ferret portal vein a perinuclear sarcoplasmic reticulum could be a factor that contributes to the high apparent nuclear Ca²⁺ levels either through a dynamic Ca²⁺ influx, or by a fura-2 signal in the sarcoplasmic reticulum masking the true nuclear [Ca²⁺]