Adsorption Isotherms of Ouabain on Hepatocytes from Normal and Diabetic (Streptozotocin‐Induced) Rats

• Published in: Journal of pharmaceutical sciences 1994-12, Vol.83 (12), p.1758-1761
• Main Authors: Bikhazi, Anwar B., Bitar, Khalil M., El‐Kasti, Muna M., Shaaban, Eman K.
• Format: Article
• Language: English
• Subjects: Adsorption; Animals; Diabetes Mellitus, Experimental - metabolism; Kinetics; Liver - cytology; Liver - metabolism; Macromolecular Substances; Male; Mathematics; Ouabain - metabolism; Ouabain - pharmacokinetics; Rats; Rats, Sprague-Dawley; Sensitivity and Specificity; Sodium-Potassium-Exchanging ATPase - metabolism; Tritium
• ISSN: 0022-3549; 1520-6017
• DOI: 10.1002/jps.2600831222

A cell surface adsorption isotherm approach is investigated with normal and diabetic (streptozotocin‐induced) rat hepatocytes utilizing mathematical modeling. Freshly prepared monodispersed viable rat hepatocytes in Ca2+‐ and Mg2+‐free phosphate buffer are obtained by collagenase perfusion and used in this study. [3H]ouabain is used as a ligand that specifically binds with the α1 and α2 isoforms of the α‐protein subunit of the hepatocyte‐membrane‐incorporated Na–K‐ATPase. The model that fits the experimental data assumes the presence of multiple receptors on the cell surface, and only when a specific fraction of the total number of one receptor have effectively reacted will the other receptor initiate reaction with the ligand. The results suggest the existence of two receptors, in normal and diabetic hepatocytes, interacting with ouabain and having different equilibrium constants. The α2 isoform interacts more strongly with ouabain than the α1 isoform in both types of cells. The α1 isoform of the diabetic hepatocytes has stronger affinity with the glycoside than the α1 isoform of the normal hepatocytes, while α2 of the diabetics shows weaker affinity than α2 of the normal hepatocytes. Therefore, the α1 and α2 isoforms of Na–K‐ATPase in hepatocyte‐cell‐membrane have different affinities for ouabain and have been conformationally and/or structurally altered in chronic diabetes.