title: Role of extracellular calcium in in vitro uptake and intraphagocytic location of macrolides.
abstract: We compared the uptakes and intracellular locations of four 14-membered-ring macrolides (roxithromycin, dirithromycin, erythromycin, and erythromycylamine) in human polymorphonuclear neutrophils (PMNs) in vitro. Intracellular location was assessed by cell fractionation and uptake kinetics in cytoplasts (granule-poor PMNs). Trapping of dirithromycin within PMN granules (up to 80% at 30 min) was significantly more marked than the intracellular trapping of the other drugs (erythromycylamine, 45% +/- 5.1%; erythromycin, 42% +/- 3.7%; roxithromycin, 35% +/- 3.0%). A new finding was that, in the absence of extracellular calcium, the uptakes of all of the macrolides by PMNs and cytoplasts were significantly impaired, by about 50% (PMN) and 90% (cytoplasts). Furthermore, inorganic Ca2+ channel blockers inhibited macrolide uptake in a concentration-dependent manner, with 50% inhibitory concentrations of 1.6 to 2.0 mM and 29 to 35 microM, respectively, for Ni2+ and La3+. The intracellular distributions of the drugs were unchanged in the presence of Ni2+ and La3+ and in Ca(2+)-free medium supplemented with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. The organic Ca2+ channel blocker nifedipine had no effect on macrolide uptake, whereas verapamil inhibited it in a time- and concentration-dependent manner. These data show the importance of extracellular Ca2+ in macrolide uptake by phagocytes and suggest a link with Ca2+ channels or a Ca2+ channel-operated mechanism.
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism*; D001711:Biotransformation / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D002614:Chelating Agents / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D018942:Macrolides; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D002121:Calcium Channel Blockers; D002614:Chelating Agents; D018942:Macrolides; D002118:Calcium