Lake Forest College, Biology, Lake Forest, IL 60045
Normal cell metabolism results in osmotic changes within a cell that, unless compensated for, can result in problematic changes in volume. Thus, in order to maintain homeostasis, cells must undergo a compensatory response. For instance, swollen cells undergo a process termed regulatory volume decrease (RVD). While its mechanisms are still not well defined, RVD consists of the efflux of specific ions, possibly signaled by the opening of stretch activated channels. Alligator mississipianis’ red blood cells (RBC) are a useful model with which to study this response because, being red blood cells, they do not require a substrate (allowing for ease of volume measurement) and, belonging to a cold-blooded reptile, they are nucleated and demonstrate a more dramatic RVD than mammalian RBCs. By exposing these cells to a variety of extracellular environments and pharmacological agents and measuring their size electronically with a Coulter Counter, our lab has found that the RVD response depends on Ca2+ influx and K+ efflux. In my experiments, I found that the PLA2 inhibitor ONO-RS-082 (10 μM) blocked RVD, indicating that this process depends on the formation of arachidonic acid (AA). In contrast, ETYA (10 μM), an agent that blocks the breakdown of AA into eicosanoids such as prostaglandins and leukotrienes, had no effect on RVD. Consistent with this, the lipoxygenase inhibitor NDGA (10 μM) also had no affect on RVD. Thus, given that PLA2 is a Ca2+-activated enzyme, our results are consistent with Ca2+ influx leading to production of AA, which in turn may then open K+ channels. This would result in K+ efflux, as well as the outward movement of osmotically obliged water, thereby decreasing cell volume. Future studies may include testing alternative eicosanoid blockers as well as determining whether and how AA affects K+ efflux.
[Abstract (DOC)]