Abstract
We tested the hypothesis that increased Sarcoplasmic reticulum (SR)
Ca content (Ca(SRT)) in phospholamban knockout mice (PLB-KO)
is because of increased SR Ca pump efficiency defined by the steady-state
SR Ca gradient. The time course of thapsigargin-sensitive ATP-dependent
(45)Ca influx into and efflux out of cardiac SR vesicles from PLB-KO
and wild-type (WT) mice was measured at 100 nm free Ca. We found
that PLB decreased the initial SR Ca uptake rate (0.13 versus 0.31
nmol/mg/s) and decreased steady-state (45)Ca content (0.9 versus
4.1 nmol/mg protein). Furthermore, at similar total SR Ca, the
pump-mediated Ca efflux rate was higher in WT (0.065 versus 0.037
nmol/mg/s). The pump-independent leak rate constant (k(leak)) was
also measured at 100 nm free Ca. The results indicate that k(leak)
was < 1\% of pump-mediated backflux and was not different among nonpentameric
mutant PLB (PLB-C41F), WT pentameric PLB (same expression level),
and PLB-KO. Therefore differences in passive SR Ca leak cannot be
the cause of the higher thapsigargin-sensitive Ca efflux from the
WT membranes. We conclude that the decreased total SR Ca in WT
mice is caused by decreased SR Ca influx rate, an increased Ca-pump
backflux, and unaltered leak. Based upon both thermodynamic and kinetic
analysis, we conclude that PLB decreases the energetic efficiency
of the SR Ca pump.
- 11087739
- action
- activation,
- adenosine
- adrenergic
- allosteric
- amp-dependent
- animals,
- atpase,
- beta-agonists,
- binding,
- biological
- biological,
- caffeine,
- calcium
- calcium,
- calcium-binding
- cardiac,
- cardiovascular,
- catalytic
- cell
- cells,
- channels,
- computer
- congestive,
- contraction,
- cultured,
- cyclic
- cytosol,
- diastole,
- dogs,
- domain,
- electric
- enzyme
- exchanger,
- factors,
- failure,
- ferrets,
- fibers,
- gov't,
- heart
- heart,
- humans,
- hydrolysis,
- inhibitors,
- intracellular
- ion
- isoproterenol,
- kinases,
- kinetics,
Users
Please
log in to take part in the discussion (add own reviews or comments).