A. A. Kaplia

Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
е-mail: kaplya@biochem.kiev.ua

The dose dependence of the Na⁺,K⁺-АТРase ouabain inhibition in the rat colon smooth muscle permeabilized microsomes has been analyzed according to the model of two independent binding sites of inhibitor to determine the activity of separate molecular forms of the enzyme that differ by affinity for cardiac glycosides. The two-phase inhibition curve with moderate content of the high-affinity activity component was revealed. The apparent inhibition constant of the low-affinity component corresponds to the value for the rat kidney microsomal Na⁺,K⁺-АТРase (α1-isoform). The specific role of the α2- and α1- Na⁺,K⁺-АТРase catalytic subunit isoforms in colonic smooth muscle electromechanical coupling is considered.