2ND MESSENGERS IN CARDIAC AND VASCULAR SMOOTH-MUSCLE CELLS

The achievements in the field of the regulation of the Ca2+ level in the cytosol of cardiomyocytes and smooth-muscle cells by second messengers are cited and discussed, with emphasis on the major differences of this regulation of the heart and blood vessels. The influence of cAMP, cGMP, Ca2+, calmodulin, diacylglycerol, and polyphosphoinositides on the work of the Ca2+ channels, Ca2+-ATPases, the plasmalemma and sarcoplasmic reticulum, as well as the Na+-Ca2+ transporter of the outer membrane, is discussed. It is emphasized that when the results of experiments conducted in vitro are extrapolated to the situation in situ, the compartmentalization of the second messengers and protein kinases in the cardiomyocytes and vascular smooth-muscle cells must be taken into consideration. The possible role of impaired phosphorylation of the membrane-bound proteins of these cells in the development of cardiac insufficiency and atherosclerosis is discussed.