The nuclear-cytoplasmic [Ca2+] gradient in single mammalian vascular smooth muscle cells

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 less than 0.001). At 3 min after 10mM caffeine, nuclear [Ca2+] decreased to 117 +/- 13 nM (n = 10, p less than 0.001), cytoplasmic [Ca2+] also decreased to 75 +/- 11 nM (n = 10, p less than 0.001) and the nuclear-cytoplasmic difference was no longer significant (p greater than 0.05). Similarly, 300pM of PDGF also abolished the nuclear-cytoplasmic [Ca2+] gradient (n = 12, p greater than 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+].