Functional alterations in adult rat myocytes after overexpression of phospholamban with use of adenovirus

An increased phospholamban (PLB)-to-sarco(endo)plasmic reticulum Ca2+-ATPas e (SERCA) ratio has been suggested to contribute to the slowing of relaxati on in failing human ventricle. We have used an adenoviral vector carrying t he sequence for PLB to increase this ratio in isolated adult rat ventricula r myocytes, and we have examined the functional consequences. With use of a denoviral vectors, the PLB content of adult rat myocytes was increased 2.73 -fold, with SERCA2a levels unchanged. Maximum contraction amplitude of PLB- overexpressing myocytes was decreased to 6.9 +/- 0.3% shortening compared w ith 11.2 +/- 0.8% for 24-h controls (Con; P < 0.001, 5 preparations, 103 my ocytes). Maximum rates of shortening and relengthening were also significan tly decreased. Ca2+ transient amplitudes were slightly depressed, and time to 50% decay of the transients was significantly increased: 237 +/- 18 (n = 14 myocytes) and 432 +/- 32 ms in Con and PLB (n = 15) myocytes, respectiv ely (P < 0.001). The amount of Ca2+ in the sarcoplasmic reticulum stores wa s reduced by 21% (P < 0.05). Relaxation was significantly slower in PLB tha n in Con myocytes when the Na+/Ca2+ exchanger was blocked but not when sarc oplasmic reticulum Ca2+ uptake was inhibited. Adenovirus infection with Ad. RSV.PLB was therefore able to produce functional changes in adult cardiac m yocytes within 24 h, consistent with overexpression of PLB and similar to t hose seen in failing human heart.