Decreased PMCA4b expression has no effect on calcium homeostasis in Meg-01 cells

Protection of rat cardiac myocytes by fructose-1,6-bisphosphate and 2,3-butanedione

Earlier studies by our group showed that fructose-1,6-bisphosphate (FBP) enhances the hypothermic preservation of rat cardiac myocytes and the functional recovery of animal hearts after hypothermic storage. However, the mechanisms involved were not clear. We extended the cardiomyocyte studies by testing whether the FBP effects were due to chelation of extracellular calcium, leading to lower intracellular levels. We also tested effects of 2,3-butanedione monoxime (BDM), pyruvate, and adenine nucleotide precursors. Cardiomyocytes were incubated in ischemic suspension at 3°C, and aliquots examined over 48 to 72 hours for retention of rod-shaped morphology, a measure of viability. Cytosolic Ca²⁺ levels were measured in some experiments. FBP at 5 mM reduced the death rate even when added after one or two days of incubation. It caused cytosolic calcium levels that were 33% lower than controls in freshly-isolated cells and 70% lower after one day of incubation. EGTA protected against cell death similarly to FBP. These results indicated that one of the mechanisms by which FBP exerts protective effects is through chelation of extracellular calcium. BDM was strongly protective and reduced cytosolic calcium by 30% after one day of incubation. As with FBP, BDM was effective when added after one or two days of incubation. BDM may be useful in combination with FBP in preserving heart tissue. Pyruvate, adenine, and ribose provided little or no protection during hypothermia.

How many Ca2+ATPase isoforms are expressed in a cell type? A growing family of membrane proteins illustrated by studies in platelets

Ca(2+) signaling plays a key role in normal and abnormal platelet functions. Understanding platelet Ca(2+) signaling requires the knowledge of proteins involved in this process. Among these proteins are Ca(2+)ATPases or Ca(2+) pumps that deplete the cytosol of Ca(2+) ions. Here, we will particularly focus on two Ca(2+) pump families: the plasma membrane Ca(2+)ATPases (PMCAs) that extrude cytosolic Ca(2+) towards the extracellular medium and the sarco/endoplasmic reticulum Ca(2+)ATPases (SERCAs) that pump Ca(2+) into the endoplasmic reticulum (ER). In the present review, we will summarize data on platelet Ca(2+)ATPases including their identification and biogenesis. First of all, we will present the Ca(2+)ATPase genes and their isoforms expressed in platelets. We will especially focus on a member of the SERCA family, SERCA3, recently found to give rise to a number of species-specific isoforms. Next, we will describe the differences in Ca(2+)ATPase patterns observed in human and rat platelets. Last, we will analyze how the expression of Ca(2+)ATPase isoforms changes during megakaryocytic maturation and show that megakaryocytopoiesis is associated with a profound reorganization of the expression and/or activity of Ca(2+)ATPases. Taken together, these data provide new aspects of investigations to better understand normal and abnormal platelet Ca(2+) signaling.