A Comparison of Calcium Dependent Contraction in Glycerinated Uterine Smooth Muscle and Cardiac Muscle

Abstract

A comparison of Ca dependent contractions in glycerinated cardiac and uterine muscle fibers and the effects of extraction in progesterone on the maximum tension developed in glycerinated uterine fibers were made. It was concluded that cardiac muscle contains an extractable factor(s) which results in Ca dependent contractions. Uterine muscle contraction, however, is either made Ca dependent by a fundamentally different factor(s) or similar factor(s) which are so tightly bound to the contractile proteins that they cannot be extracted. In addition it was concluded that the low tension generated by glycerinated uterine fibers was probably not due to breakdown and release of proteolytic enzymes from lysosomes since progesterone which supposedly inhibits lysosome breakdown had no effect on the maximum tension generated.