Location of the active site of rat vascular semicarbazide-sensitive amine oxidase

Abstract

Semicarbazide-sensitive amine oxidase (SSAO) activity in rat vascular smooth muscle cells is associated extensively with the plasmalemma. To determine which side of the plasmalemma the active sites of these enzymes face, the non-permeating agent, diazotised sulphanilic acid (DSA; 4.4 mM) was perfused through the isolated mesenteric arterial bed of the rat, in an attempt to inactivate only those active sites facing extracellularly. DSA perfusion abolished the pressor responses to noradrenaline via inactivation of extracellular α1 receptors but had no effect on cytosolic lactate dehydrogenase activity. SSAO activity, estimated by perfusing [14C] benzylamine, was reduced following DSA perfusion to 55.9 ± 4.9% of that in control beds and to 52.4 ± 6.0% in homogenates of these vessels. These results suggest that almost half of SSAO active sites in rat mesenteric arteries face outwards.