Increase in ATPase activity in red cell membranes as a function of freezing regimen

Activity of Na+/K+- and Ca2+-ATPases in human erythrocyte membranes: Protocol improvement, relation to cholesterol content, and effects of polyphenols

It is known that the activities of Na+/K+- and Ca2+-ATPases in the plasma membrane with an excess of cholesterol are compromised. Our main goal was to find out whether quercetin, resveratrol, or caffeic acid, in the nano- and low micromolar concentration ranges, can improve the ATPase activity in human erythrocyte membranes with excess cholesterol. These molecules belong to different chemical classes of polyphenols and are widely present in plant foods. Also, due to some variations in the protocol for determining the ATPase activity, we first analyzed several key parameters of the protocol to improve the accuracy of the results. The activities of Na+/K+- and Ca2+-ATPases were reduced in membranes with moderate and high cholesterol levels compared to membranes from normocholesterolemic subjects (p < 0.01). All three polyphenols affected the ATPase activity in a similar biphasic manner. Namely, the ATPase activity gradually increased with increasing polyphenol concentration up to 80-200 nM, and then gradually decreased with further increase in polyphenol concentration. Moreover, the stimulating effect of the polyphenols was highest in membranes with high cholesterol content, making ATPase activity values close/equal to those in normal cholesterol membranes. In other words, quercetin, resveratrol, and caffeic acid at nanomolar concentrations were able to improve/restore the functioning of Na+/K+- and Ca2+-ATPases in erythrocyte membranes with high cholesterol levels. This suggests a common membrane-mediated mechanism of action for these polyphenols, related to the content of membrane cholesterol.

Protein kinase activity in erythrocyte ghosts of patients with myotonic muscular dystrophy

Myotonic muscular dystrophy is a disorder of humans that involves many organ systems. Physiological studies have suggested that the fundamental defect is of membrane origin. Heretofore, no reproducible metabolic abnormalities have been demonstrated. In the present studies we used erythrocyte ghosts as a convenient source of purified membranes that do not possess changes of denervation, dystrophy, and fibrosis that might complicate the interpretation of muscle membrane changes. Our experiments demonstrated a significant difference in the phosphorylation of erythrocyte ghost protein by [gamma-(32)P]ATP, with endogenous protein kinase of erythrocyte membrane as the enzyme source. After ghosts were kept for 1 week at -20 degrees , phosphorylation of membrane protein in eight controls was twice as high as endogenous protein kinase activity measured in fresh preparations. No stimulation was seen in preparations from seven myotonic dystrophy patients from three different families. This reproducible difference in normal and myotonic membranes may represent an important new approach to studies of this debilitating inborn error of metabolism.