Influence of NAADP and bafilomycine A1 on activity of ATPase in liver postmitochondrial fraction

Recycling of the endo-lysosomal organelles occur by permanent in the cell. This store is thought to be the acidic store because V-type of H+-ATPase is responsible for their acidification. Bafilomycine A1 is a selective inhibitor of vacuolar H+ ATPase, and is often used as anticancer drug. However, it is not clear if applying of bafilomycine A1 is safe for normal cells.Endolysosomes are important cellular Ca2+ storage, sensitive to nicotinic acid adenine dinucleotide phosphate (NAADP). Hepatocytes were shown to have NAADP-sensitive acidic store. But the correlation between acidic store and endoplasmatic reticulum or plasmatic membrane during endo-lysosomal organelles recycling and fusion is still unknown. The main goal of this study was to examine influence of bafilomycine A1 and NAADP on activity of Na+/K+-ATPase, basal Mg2+-ATPase and Ca2+-ATPase of plasmatic membrane (PM) and endoplasmatic reticulum (ER) for better understanding of the relationship between acidic organelles and PM/ER. Besides possibility of bafilomycineA1 applying as anticancer drug is examined. All experiments were conducted using rat liver postmitochondrial fraction.It was shown that SERCA activity is increasing under bafilomycine A1 presence, as well as NAADP. At the same time, changes in PMCA activity was not found. Preincubation of rat liver postmitochondrial fraction with bafilomycine A1 completely prevented NAADP-induced increasing of SERCA activity. Bafilomycine A1 decreased activity of Na+/K+-ATPase and amplificated NAADP-induced decreasing of this pump. Applying of NAADP caused more intensive decrease in Na+/K+-ATPase activity after preincubation of this fraction with bafilomycine A1. It was also shown that bafilomycine A1 caused increasing of basal Mg2+-ATPase activity and NAADP intensify bafilomycine A1-induced changes of function of this pump. These effects are realized due to changes of pH inside the endo-lysosomal ogranels, acidification of incubation medium, as well as calcium concentration in local contact sites. A conclusion was made that NAADP-sensitive store is bafilomycine A1-sensitive, which also has direct contact sites to ER, but not to PM. Besides, existing of NAADP-sensitive, but bafilomycine-insensitive store in this fraction is supposed, which is more likely represented by endosomes. So, applying bafilomycine A1 in anticancer therapy may cause a damage of endo-lysosomal organelles recycling in healthy cells.