Characteristics of Plasmalemma Alkaline Phosphatase of Rat Mesenteric Artery

Abstract

General characteristics of alkaline phosphatase activity of the plasma membrane-enriched fraction isolated from rat mesenteric arteries were investigated. The vascular smooth muscle plasmalemma alkaline phosphatase is a metalloenzyme which is strongly inhibited by chelating agents and this inhibition can be completely overcome by addition of Mg²⁺ or Ca²⁺. Zn²⁺ only partially reactivates the enzyme in the presence of low concentrations of EDTA. The enzymatic hydrolysis of p-nitrophenyl phosphate, β-glycerophosphate, α-glycerophosphate, or 3’-adenosine monophosphate showed an optimal activity in the alkaline region between pH 9 and 11. The alkaline phosphatase activity is distinctly different from the plasmalemma ATPase and 5’-nucleotidase activities with respect to their pH dependence, influence by added divalent metal ions and stability against heat inactivation. Vanadate ion, being structurally similar to the transition state analog of the phosphoryl group, potently inhibits alkaline phosphatase with an apparent Ki of 1.5 µM. The altered alkaline phosphatase activity of vascular smooth muscle in relation to its possible physiological function and pathophysiological manifestation associated with hypertensive disease are discussed.

Alkaline Phosphatase Activity Is a Key Determinant of Vascular Responsiveness to Norepinephrine

“…However, whether TNAP regulates vascular responsiveness in other vascular beds and the mechanisms involved remain unknown. Because the mesenteric vascular bed expresses high TNAP activity, 18 here we tested, both in vitro and in vivo, the hypothesis that TNAP modulates vascular responsiveness to norepinephrine in the rat mesentery. We also investigated the mechanism by which TNAP modulates vascular responses to norepinephrine.…”