Effects of phospholemman downregulation on contractility and [Ca(2+)]i transients in adult rat cardiac myocytes.

Phospholemman (PLM) expression was increased in rat hearts after myocardial infarction (MI). Overexpression of PLM in normal adult rat cardiac myocytes altered contractile function and cytosolic Ca2+ concentration ([Ca2+]i) homeostasis in a manner similar to that observed in post-MI myocytes. In this study, we tested whether PLM downregulation in normal adult rat myocytes resulted in contractility and [Ca2+]i transient changes opposite to those observed in post-MI myocytes. Compared with control myocytes infected with adenovirus (Adv) expressing green fluorescent protein (GFP) alone, myocytes infected with Adv expressing both GFP and rat antisense PLM (rASPLM) had 23% less PLM protein (P < 0.012) at 3 days, but no differences were found in sarcoplasmic reticulum (SR) Ca2+-ATPase, Na+/Ca2+ exchanger (NCX1), Na+-K+-ATPase, and calsequestrin levels. SR Ca2+ uptake and whole cell capacitance were not affected by rASPLM treatment. Relaxation from caffeine-induced contracture was faster, and NCX1 current amplit...