calcium-handling proteins in cardiac myocytes. I. Experimental stud-

genetic experimental approaches, de novo expression of parvalbumin (Parv) and overexpression of sarco(endo)plasmic reticulum Ca2-ATPase (SERCA2a), have been shown to increase relaxation rates in myocardial tissue. However, the relative effect of Parv and SERCA2a on systolic function and on -adrenergic responsiveness at varied pacing rates is unknown. We used gene transfer in isolated rat adult cardiac myocytes to gain a fuller understanding of Parv/SERCA2a function. As demonstrated previously, when Parv is expressed in elevated concentration (0.1 mM), the transduced myocytes showed a reduction in sarcomere-shortening amplitude: 129 17, 81 8, and 149 14 nm for control, Parv, and SERCA2a, respectively. At physiological temperature, shortening amplitude responses of Parv and SERCA2a myocytes to the -adrenergic agonist isoproterenol (Iso) were not statistically different from that of control myocytes. However, in SERCA2a myocytes, in which baseline was slightl