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

Summary 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.     

Morphology and behaviour of cultured AËdes aegypti mosquito cells

Cultured Aëaes aegypti mosquito cells dissplay three distinct growth stages. First a monolayer is formed, then some of the cells aggregate, and finally there appear vesicular bodies. Cells composing the aggregates and vesicles are endowed with the capacity to produce secretory substances such as melanin, and a chitin-like substance. These properties are retained by the cells even after over 170 passages in vitro.     

Concanavalin A receptor capping in mouse myeloma and hybridoma

Concanavalin A capping was studied in immunoglobulin-secreting hybridomas derived from fusion of mouse myeloma NSO cells with mouse spleen lymphocytes. The cells of the parental populations differed significantly in capping ability (low in myeloma cells and high in the lymphocytes). Among the hybridoma cells tested, several clones showed low capping, similar to that of the myeloma cells, some showed a good degree of capping, similar to that of the lymphocytes and other clones expressed an intermediate capping response. Capping was significantly increased in hybridoma clones of intermediate capping ability following in vivo intraperitoneal growth. A possible relationship of the variation in capping response to cell motility and to metastatic capacity is pointed out.     

Evaluation of the Fermi equation as a model of dose-response curves

 When plotted in linear coordinates, the dose-response curves of microorganisms exposed to a lethal agent, such as radiation or a toxic substance, often have a characteristic sigmoid shape. Irrespective of whether they are very narrow or broad they can be described by the Fermi function, which is a mirror image of the logistic function, i.e. S(X)=1/{1+ exp [(X−X _c)/a]} where S(X) is the fraction of the surviving organisms, X the dose of the lethal agent, X _c a characteristic dose marking the inflection point of S(X), which corresponds to 50% mortality, and a a measure of the steepness of the survival curve around X _c. It is demonstrated that, if the susceptibilities of the individual organisms, expressed in terms of a characteristic lethal dose, have a symmetric unimodal distribution, the dose-response curve of the population has a Fermian sigmoid shape. It is also shown that the mode and variance of the distribution can be estimated from the shape parameters of the Fermian survival curve, X _c and a. Received: 7 November 1995 / Received last revision: 11 April 1996 / Accepted: 29 April 1996