Effect of ablation of phospholamban on dynamics of cardiac myocyte contraction and intracellular Ca2+.
We compared mechanical activity and Ca2+ transients of ventricular myocytes isolated from wild-type and phospholamban (PLB)-deficient mouse hearts in control conditions and during beta-adrenergic stimulation. Compared with wild-type controls, cells isolated from PLB-deficient mouse hearts showed 1) a 2-fold increase in extent of cell shortening, 2) a 3-fold increase in maximal shortening velocity, and 3) a 3.4-fold increase in maximal relengthening velocity. PLB-deficient myocytes also demonstrated significant increases in the peak amplitude of the fura 2 fluorescence ratio and the rates of rising and falling phases of the Ca2+ transient. The fura 2 diastolic ratios were similar in both groups, suggesting no change in intracellular Ca2+ during diastole. In PLB-deficient myocytes, 0.05 microM isoproterenol induced an increase in the twitch amplitude by 152 +/- 11% (n = 6) compared with 290 +/- 31% (n = 6) in wild-type cells. Maximal shortening velocity was increased by 183 +/- 10% (n = 6) in PLB-deficient myocytes, compared with 398 +/- 62% (n = 6) in wild-type cells. The isoproterenol-induced increase in maximum relengthening velocity was increased by 168 +/- 8% (n = 6) in PLB-deficient cells compared with 445 +/- 71% (n = 6) in wild-type myocytes. In both groups, these changes in contractile parameters were accompanied by changes in the Ca2+ transient. Our results indicate that phosphorylation of sites other than PLB may play an important role in regulation of contraction-relaxation dynamics of heart cells responding to beta-adrenergic stimulation.
Wolska
B M
BM
Department of Physiology and Biophysics, University of Illinois at Chicago, College of Medicine 60612, USA.
Stojanovic
M O
MO
Luo
W
W
Kranias
E G
EG
Solaro
R J
RJ
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000172:deficiency*; D005456:Fluorescent Dyes; D016257:Fura-2; D007425:Intracellular Membranes / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D000099211:Phospholamban
D000318:Adrenergic beta-Agonists; D002118:Calcium; D002135:Calcium-Binding Proteins; D005456:Fluorescent Dyes; D016257:Fura-2; D007545:Isoproterenol; D000099211:Phospholamban