Na⁺-K⁺ATPase in rat vascular smooth muscle cell grown in vitro

This study has focused on the characteristics of the Na⁺-K⁺-ATPase in in vitro preparations of vascular smooth muscle cells (VSMCs) derived from the rat carotid artery. The maximum velocity of enzyme reaction (V(max)) for the specific activity of the enzyme in VSMCs' preparations was 2.36 ± 0.04 (SE) μmol P(i).mg cell protein^-1.h^-1 or 0.82 ± 0.02 μmol P(i).10⁶ cells^-1.h^-1. The activation of the enzyme by potassium, sodium and ATP has been investigated. The half-maximal values for potassium and sodium activation of the enzyme in the preparations were 1.18 and 10-20 meq/l, respectively. The respective V(max) values for potassium and sodium activation were reached at concentrations of 4-10 and 80-100 meq/l. The Michaelis constant for ATP was 0.83 mM. Calcium exerted a potent inhibition of the activity of the enzyme (I₅₀ at 1 mM). It has been concluded that the Na⁺-K⁺-ATPase kinetic pattern in in vitro preparations of VSMCs is quite similar to that observed in homogenates or subcellular fractions of other tissues.