TRANSPLASMA MEMBRANE REDOX SYSTEM OF HL-60 CELLS IS CONTROLLED BY CAMP

Transplasma membrane redox activity of HL-60 cells was determined by m easuring the prevention of ascorbate chemical oxidation. The ascorbate free radical produced as the first step of ascorbate oxidation was re duced back by the transplasma membrane electron transport system, caus ing then the regeneration of extracellular ascorbate. Agents that incr ease intracellular cAMP, such as forskolin and dibutyryl cAMP (db-cAMP ), increased the rate of ascorbate regeneration by HL-60 cells. Also, the phosphodiesterase-resistant cAMP analogue S(p)-cAMP-S (agonist of the protein kinase A) increased the electron flow to the ascorbate fre e radical at the plasma membrane. R(p)-cAMP-S, antagonist of the prote in kinase A, partially inhibited the redox activity of cells and aboli shed the effect of S(p)-cAMP-S. Inhibition obtained after preincubatio n of cells in R(p)-cAMP-S was reversed by S(p)-cAMP-S. Tunicamycin, a compound that inhibited the electron flow to the ascorbate free radica l at the plasma membrane, also reduced the response of transplasma mem brane redox system to S(p)-cAMP-S. Lactate slightly affected the ascor bate regeneration in nonstimulated cells, but showed a significant eff ect on S(P)-cAMP-S-stimulated plasma membrane electron flow. We show h ere a role for CAMP in the short-term modulation of transplasma membra ne redox system measured as the regeneration of ascorbate at the cell surface of HL-60 cells, probably mediated by cAMP-dependent protein ki nases.