Long ultradian rhythms in red blood cells and ghost suspensions: possible involvement of cell membrane

Oscillations in glyceraldehyde-3-phosphate dehydrogenase (GAPD) and glucose-6-phosphate dehydrogenase (G6PD) activities were recorded in suspensions of intact human red blood cells (RBCs) exposed to various light regimens. The periods of these oscillations, defined as "long ultradian," ranged between 13 and 18 h regardless of light regimen. The patterns of enzymatic activities were the same when assayed at each time point, in full hypotonic hemolysates, and membrane-free hemolysates. However, if hemolysates were prepared by sonication the activity pattern did not exhibit significant oscillations and the activity was higher than that recorded in hypotonic hemolysates. The observed rhythms may reflect a time-dependent attachment and detachment of enzyme molecules from cell membrane, suggesting that at the bound state the enzyme molecules are (temporarily) inactive. Oscillations with similar long ultradian periods were also observed in Ca++ concentration of suspended RBCs and in the binding of Ca++45 to human RBC ghosts. Treatment of the RBCs with A2C or Diamide before the preparation of the ghosts changed or distorted the rhythmic pattern of Ca++45 binding. These results point to the role of the membrane in processing the long ultradian oscillations. The relation between this type of oscillations to circadian rhythm is discussed.