The overall goal of this program project is to generate new knowledge concerning specific molecular mechanisms that modulate the major functions of cardiac and vascular muscle, including contractility, growth and cellular proliferation. The unifying subtheme selected for this competitive renewal is: Ca2+ and protein phosphorylation: interacting subcellular mechanisms that modulate contractile and growth properties of cardiac and vascular muscles. This group of investigators will pursue, through interactive and collaborative studies, four major objectives under the general subtheme: 1) To evaluate the role of selected cell cycle regulatory proteins in the induction or maintenance of cardiac cellular proliferation by targeted expression in transgenic animal models; 2) To delineate the mode of regulation of key protein phosphatases implicated in modulation of growth, cell cycling and contractile function of cardiac and vascular cells; 3) To determine the role of Ca2+ in cardiac muscle contraction and cellular proliferation via specific investigation of intracellular uptake and release mechanisms; and 4) To identify and characterize specific steps in the vascular cell cycle that are dependent upon irreversible protein modification via Ca2+-dependent proteolysis. Four projects and three core units have been assembled to address these objectives. Project 1 investigates Ca2+-dependent cysteine proteases in regulation of the vascular cell cycle. Project 2 explores the mechanisms of cardiomyocyte proliferation by expressing mutant growth regulatory proteins in transgenic mice. Project 3 analyzes Ca2+ transport mechanisms in cardiac sarcoplasmic reticulum via structural/functional analysis of the proteins, phospholamban and Ca 2+ ATPase. Project 4 studies the regulation of phosphoprotein phosphatases common to both cardiac and vascular tissues that modulate contractility and growth. Collectively, this Program Project applies the methodologies of protein biochemistry and molecular biology to investigate highly fundamental mechanisms of cellular regulation in cardiovascular tissues. The common use of transgenic animal models to explore protein function in a physiological milieu promises to yield novel observations at several levels including both growth and contractile function. The basic studies proposed have important implications to the health-related problems of heart failure, regeneration of cardiac muscle and modulation of vascular tissue growth.