RT Journal Article
SR Electronic
T1 A Bioactive Metabolite of Benzo[<em>a</em>]pyrene, Benzo[<em>a</em>]pyrene-7,8-dione, Selectively Alters Microsomal Ca<sup>2+</sup> Transport and Ryanodine Receptor Function
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 506
OP 513
DO 10.1124/mol.59.3.506
VO 59
IS 3
A1 Isaac N. Pessah
A1 Chris Beltzner
A1 Scott W. Burchiel
A1 Gopishetty Sridhar
A1 Trevor Penning
A1 Wei Feng
YR 2001
UL http://molpharm.aspetjournals.org/content/59/3/506.abstract
AB Polycyclic aromatic hydrocarbons are environmental pollutants known to be carcinogenic and immunotoxic. In intact cell assays, benzo[a]pyrene (B[a]P) disrupts Ca2+ homeostasis in both immune and nonimmune cells, but the molecular mechanism is undefined. In this study, B[a]P and five metabolites are examined for their ability to alter Ca2+ transport across microsomal membranes. Using a well-defined model system, junctional SR vesicles from skeletal muscle, we show that a single o-quinone metabolite of B[a]P, B[a]P-7,8-dione, can account for altered Ca2+ transport across microsomal membranes. B[a]P-7,8-dione induces net Ca2+ release from actively loaded vesicles in a dose-, time-, and Ca2+-dependent manner. In the presence of 5 μM extravesicular Ca2+, B[a]P-7,8-dione exhibited threshold and EC50 values of 0.4 and 2 μM, respectively, and a maximal release rate of 2 μmol of Ca2+ min−1 mg−1. The mechanism by which B[a]P-7,8-dione enhanced Ca2+ efflux was further investigated by measuring macroscopic fluxes and single RyR1 channels reconstituted in bilayer lipid membranes and direct measurements of SERCA catalytic activity. B[a]P-7,8-dione (≤ 20 μM) had no measurable effect on initial rates of Ca2+ accumulation in the presence of ruthenium red to block ryanodine receptor (RyR1), nor did it alter Ca2+-dependent (thapsigargin-sensitive) ATPase activity. B[a]P-7,8-dione selectively altered the function of RyR1 in a time-dependent diphasic manner, first activating then inhibiting channel activity. Considering that RyR1 and its two alternate isoforms are broadly expressed in mammalian cells and their important role in Ca2+-signaling, the present results reveal a mechanism by which metabolic bioactivation of B[a]P may mediate RyR dysfunction of pathophysiological significance.