RENAISSANCE OF CYTOCHEMICAL-LOCALIZATION OF MEMBRANE ATPASES IN THE MYOCARDIUM

ATPases of cardiac cells are known to be among the most important enzy mes to maintain the fluxes of vital cations by hydrolysis of the termi nal high-energy phosphate of ATP. Biochemically the activities of Ca2-pump ATPase, Ca2+/Mg2+-ecto ATPase, Na+,K+-ATPase and Mg2+-ATPase are determined in homogenates and isolated membranes as well as in myofib rillar and mitochondrial fractions of various purities. Such technique s permit estimation of enzyme activities in vitro under optimal condit ions without precise enzyme topography. On the other hand, cytochemica l methods demonstrate enzyme activity in situ, but not under optimal c onditions. Until recently several cytochemical methods have been emplo yed for each enzyme in order to protect its specific activity and prec ise localization but the results are difficult to interpret. To obtain more consistent data from biochemical and cytochemical point of view, we modified cytochemical methods in which unified conditions for each ATPase were used. The fixative solution (1% paraformaldehyde - 0.2% g lutaraldehyde in 0.1 M Tris Base buffer, pH 7.4), the same cationic co ncentrations of basic components in the incubation medium (0.1 M Tris Base, 2 mM Pb(NO2)(3), 5 mM MgSO4, 5 mM ATP) and selective stimulators or inhibitors were employed. The results reveal improved localization of Ca2+-pump ATPase, Na+-K(+)ATPase and Ca2+/Mg2+-ecto ATPase in the cardiac membrane.