QUANTITATIVE CONTRIBUTION OF THE ACID PRODUCTION TO THE INTRACELLULARACIDIFICATION IN HUMAN NEUTROPHILS STIMULATED BY N-FORMYL-METHIONYL-LEUCYL-PHENYLALANINE

A chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine (fMLP), induced an acidification of cytosol by about 0.05 pH units in 30 sec followed by an alkalinization in human neutrophils. The quantitative c ontribution of acid production to the acidification was studied. The s uperoxide (O-2(-)) production stimulated by fMLP was not involved in t he acidification because the production of acids in neutrophils from p atients with chronic granulomatous disease who do not produce O-2(-), was the same as that in normal neutrophils. The intracellular acidific ation was completely inhibited by deoxyglucose, suggesting that energy metabolism enhanced upon stimulation by fMLP might be the main source of the acidification. Although enhancement of the lactate formation b y fMLP was 0.8 nmol/10(6) cells, which could lower intracellular pH by 0.08 pH units, the lactate production could not explain the initial a cidification because the production of lactate started at 1 min after the stimulation while the intracellular acidification began immediatel y after the stimulation. Mitochondrial respiratory inhibitors such as KCN and rotenone had no effects on the fMLP-induced intracellular acid ification. The fMLP-induced production of CO, in 30 sec through the he xose monophosphate shunt was only 2.6 pmol/10(6) cells, which was calc ulated to decrease intracellular pH by only 0.0014. Thus, changes of e nergy metabolism induced by fMLP does not explain the acidification.