The sodium pump Na,K-ATPase, located in the plasma membrane of all animal cells, is a member of a family of ion-translocating ATPases that share highly homologous catalytic subunits. In this family, only Na,K-ATPase has been established to be a heterodimer of catalytic (alpha) and glycoprotein (beta) subunits. The beta subunit has not been associated with the pump's transport or enzymatic activity, and its role in Na,K-ATPase function has been, until recently, a puzzle. In this review we describe what is known about the structure of beta and summarize evidence that expression of both alpha and beta subunits is required for Na,K-ATPase activity, that inhibition of glycosylation causes a decrease in accumulation of both alpha and beta subunits, and we provide evidence that pretranslational up-regulation of beta alone can lead to increased abundance of sodium pumps. These findings are all consistent with the hypothesis that the beta subunit regulates, through assembly of alpha beta heterodimers, the number of sodium pumps transported to the plasma membrane.

A drawback of extensive coxib use for antitumor purposes is the risk of life-threatening side effects that are thought to be a class effect and probably due to the resulting imbalance of eicosanoid levels. 2,5-Dimethyl-celecoxib (DMC) is a close structural analogue of the selective cyclooxygenase-2 inhibitor celecoxib that lacks cyclooxygenase-2 -inhibitory function but that nonetheless is able to potently mimic the antitumor effects of celecoxib in vitro and in vivo. To further establish the potential usefulness of DMC as an anticancer agent, we compared DMC and various coxibs and nonsteroidal anti-inflammatory drugs with regard to their ability to stimulate the endoplasmic reticulum (ER) stress response (ESR) and subsequent apoptotic cell death. We show that DMC increases intracellular free calcium levels and potently triggers the ESR in various tumor cell lines, as indicated by transient inhibition of protein synthesis, activation of ER stressassociated proteins GRP78/BiP, CHOP/GADD153, and caspase-4, and subsequent tumor cell death. Small interfering RNA -mediated knockdown of the protective chaperone GRP78 further sensitizes tumor cells to killing by DMC, whereas inhibition of caspase-4 prevents druginduced apoptosis. In comparison, celecoxib less potently replicates these effects of DMC, whereas none of the other tested coxibs (rofecoxib and valdecoxib) or traditional nonsteroidal anti-inflammatory drugs (flurbiprofen, indomethacin, and sulindac) trigger the ESR or cause apoptosis at comparable concentrations. The effects of DMC are not restricted to in vitro conditions, as this drug also generates ER stress in xenografted tumor cells in vivo, concomitant with increased apoptosis and reduced tumor growth. We propose that it might be worthwhile to further evaluate the potential of DMC as a non-coxib alternative to celecoxib for anticancer purposes.

Horse blood has a higher tendency to form red blood cell (RBC) aggregates compared with human blood, with this enhanced aggregation previously attributed to differences in plasma factors. Our results confirm this observation and further indicate that washed horse RBC also have a significantly higher aggregation tendency in dextran 70 solutions (i.e., horse RBC have a higher “aggregability”). In contrast, the aggregation tendency of rat RBC, both in autologous plasma and in dextran 70, is significantly less compared with human and horse RBC. Other rheological findings for horse and rat RBC include smaller changes in RBC deformation indexes over the same shear stress range and a lower RBC shape recovery time constant. Rat RBC also had higher two-phase aqueous polymer partition coefficients, suggesting a higher surface charge. Membrane protein analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed marked differences: 1) band 4.2 protein was lacking in horse RBC membranes, and 2) carbohydrate groups have different distributions in human, rat, and horse RBC, as indicated by different patterns in periodic acid-Schiff-stained protein bands. Our results clearly indicate significant differences in RBC aggregability among the three species and indicate that cellular factors contribute importantly to these differences. Furthermore, they suggest that systematic studies of blood and RBC from different species should provide insight into the mechanism(s) of RBC aggregation.

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