PHARMACOLOGICAL STUDIES ON MECHANISMS INVOLVED IN CA2+ OSCILLATIONS IN RAT MEGAKARYOCYTES

Extracellular application of ATP evoked the oscillatory K+ currents (I -KCa) reflecting oscillation in cytoplasmic Ca2+ concentration ([Ca2+] (i)) of megakaryocyte isolated from rat bone marrow. We have reported that the [Ca2+](i) oscillation was regulated by intracellular Ca2+-pum ping activity (Uneyama, H., C. Uneyama and N. Akaike, 1993, J. Biol. C hem. 268, 168). Here we found that the Ca2+ pump of the megakaryocyte could be divided into at least two classes according to the sensitivit y to phosphorylation-modulating drugs. The effects of protein kinase C and cyclic AMP-dependent protein kinase are complementary, and the ef fect of Ca2+/calmodulin is independent of the above two kinases. In ad dition, this is the first report concerning the physiological regulati on of Ca2+-ATPase in living cells.