S. V. Bychkova¹, T. I. Chorna²

¹Ivan Franko National University of Lviv, Ukraine;
²National Centre for Biological Sciences, Tata Institute
of Fundamental Research, Bangalore, India;
e-mail: s.bychkova@gmail.com

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a nucleotide that is potent to release calcium from intracellular stores in different cell types. NAADP was shown to target specific type of intracellular store namely endolysosomal system or acidic store. Despite intense studies, its effect on endoplasmatic reticulum (ER) still remains to be elucidated. The main aim of our work was to investigate NAADP-sensitive store in permeabilized rat hepatocytes monitoring the level of Ca²⁺ inside intracellular organelles using chlorotetracycline (CTC). We have shown that NAADP triggered changes of stored Ca²⁺ in rat hepatocytes are dependent on concentration of EGTA-Ca²⁺-buffer in cell incubation medium, i.e. the higher is the EGTA concentration in incubation medium the smaller or absent is the effect of NAADP. Besides, the effect of NAADP was more pronounced upon cells pretreatment with the inhibitory concentration of ryanodine (100 µM). This might suggest that the effect of NAADP is dependent on ER luminal calcium. We have also found that NAADP-evoked Ca²⁺ release in permeabilized hepatocytes is sensitive to nigericin, bafilomycin A and thapsigargin. Additionally, NAADP triggered changes in stored Ca²⁺ were completely abolished by NED-19 as antagonist of NAADP.