Membrane adenosine triphosphatase activity of vascular smooth muscle

Abstract

Differential centrifugation of rabbit aorta homogenates prepared in 0.25 M sucrose-30 mM histidine provided heavy, intermediate and light fractions. The light (microsomal) fraction was characterized by low cytochrome c oxidase, malate dehydrogenase and NADPH cytochrome c reductase activities and high NADH cytochrome c reductase and adenosine triphosphatase (ATPase) activities. Microsomal MgATPase differed from large granule MgATPase in the response to desoxycholate, Triton X-100, chlorpromazine, oligomycin and 2,4-dinitrophenol. The microsomal fraction contained significant amounts of guanosine and inosine triphosphatase activity, inhibited by Triton X-100. Mitochondrial and microsomal adenosine triphosphatase activity was stimulated by sodium hydrosulfite. Thiol inhibitors were without effect on microsomal adenosine triphosphatase activity. No monovalent cation dependence could be demonstrated, even in the presence of azide. These observations are discussed in reference to the membrane localization of microsomal MgATPase, the nature of aortic smooth muscle light microsomal fractions and the significance of such enzyme activity in monovalent cation transport at the smooth muscle membrane.