Circadian rhythm in the membrane of circulating human blood cells: microviscosity and number of benzodiazepine binding sites. A search for regulation by plasma ions, nucleosides, proteins or hormones.

Abstract

Circadian rhythms in both the number of peripheral type binding sites for benzodiazepines in platelet membranes and the microviscosity of the erythrocyte membrane were demonstrated in 7 healthy men. Neither variable appeared to be linked to each other, or regulated by the plasma concentrations of total or free cortisol, testosterone, potassium, magnesium, calcium, cAMP, cGMP or proteins or by the erythrocytic concentration of magnesium or potassium or by the plasma cAMP:cGMP ratio or by the ratio of intra-erythrocyte:plasma concentrations of potassium or magnesium. A highly significant negative correlation was found between the microviscosity of the erythrocyte membrane and the activity of the membrane-bound enzyme, methyltransferase I. Such a correlation was validated both on raw data and on 24 hr-means (r = 0.84; P less than 0.01). A circadian rhythm in the activity of this enzyme was also demonstrated. Moreover, a highly significant correlation was also found between plasma transcortin concentration (TRC) and microviscosity (r = 0.50, P less than 0.01), and between TRC and methyltransferase I activity (r = 0.61, P less than 0.01). Such findings may constitute clues towards the understanding of the regulation of the circadian rhythm in the fluidity of the red blood cell membrane in man and guide future steps with regard to the role of this rhythm upon the availability of drug binding sites at the cell surface.