Abstract 407: Endothelin-1 Potentiates Nuclear Calcium Transients via IP3-Dependent Calcium Release from Perinuclear Calcium Stores
Nuclear [Ca2+] is a key factor in the regulation of gene expression. Endothelin-1 (ET) might alter gene expression via selective regulation of nuclear [Ca2+]. We tested the hypothesis that ET regulates nuclear [Ca2+] in cardiac myocytes via IP3-dependent Ca2+release from perinuclear Ca2+ stores.
METHODS Rabbit atrial myocytes were stimulated at 0.7 Hz. Cytosolic and nuclear [Ca2+] were imaged using fast two-dimensional confocal microscopy and fluo-4 fluorescence. Ca2+load of cytosolic (i.e. sarcoplasmic reticulum, SR) and perinuclear Ca2+stores was assessed by application of 20mM caffeine. Fractional Ca2+ release from SR and perinuclear stores was calculated as ratio of the amplitudes of electrically stimulated and caffeine-induced [Ca2+] transients.
RESULTS ET (10nM) increased cytosolic and nuclear [Ca2+] transients. After 10min, the ET-induced increase in [Ca2+] transients amounted to 31±7% in cytosol and to 44±8% in nucleus (P<0.01), indicating potentiation of nuclear [Ca2+] transients by ET. By contrast, when cytosolic [Ca2] transients were augmented by either elevation of extracellular [Ca2+] (to 4mM, n=6) or by equi-effective concentrations of isoproterenol (2–10nM, n=10), there was no potentiation of nuclear [Ca2+] transients. Furthermore, at low concentrations (0.1nM, n=6), ET elicited a selective increase in nuclear [Ca2+] transients (+9±4%, P<0.05) without affecting cytosolic [Ca2+] transients. Inhibition of ETA receptors (2.5x10−7M BQ123, n=10), phospholipase C (3x10−6M U73122, n=7), or IP3 receptors (3x10−6M 2APB, n=10) attenuated or abolished the increases in cytosolic and nuclear [Ca2+] transients elicited by 10nM ET (all P<0.05). Ca2+ load of SR and perinuclear stores remained almost unchanged during ET treatment, but fractional Ca2+ release was significantly increased from 54±8% to 90±11% in SR and from 46±7% to 87±12% in perinuclear stores (n=5).]
CONCLUSIONS In atrial myocytes, ET potentiates nuclear [Ca2+] transients via a pathway involving ETA receptors, phospholipase C, and IP3 signaling. Increased fractional Ca2+ release via IP3 receptors from perinuclear stores, most likely the nuclear envelope, underlies the ET-induced increase in nuclear [Ca2+] transients.