Alkalinization of the intralysosomal pH by clindamycin and its effects on neutrophil function

Clindamycin is concentrated within human neutrophils and their lysosomes because the intralysosomal pH is highly acidic and this antibiotic behaves as a weak base. We have examined the ability of clindamycin to buffer (alkalinize) the intralysosomal pH and studied the consequences of alterations of lysosomal pH on neutrophil functions. At therapeutic concentrations of clindamycin (0.01 mM), we observed no effect on intralysosomal pH as monitored by the distribution and fluorescence of a weakly basic fluorescent probe 9-aminoacridine. However, at higher concentrations (1.0 mM), clindamycin alkalinized the intralysosomal pH and inhibited neutrophil lysosomal degranulation to several stimuli, and superoxide production in response to phorbol myristate acetate. Neutrophil locomotion was unaffected even at concentrations of clindamycin which increased the intralysosomal pH. We conclude that clindamycin accumulates in acidic neutrophil lysosomes and, at high concentrations, alkalinizes the intralysosomal pH. Coincident with lysosomal alkalinization there is inhibition of secretion and respiratory burst activity suggesting that intact lysosomal pH regulation is important for these functions. Clindamycin provides a useful tool to examine the relationships between weak base uptake, lysosomal pH and neutrophil functions.