E. Mtairag et al., ROLE OF EXTRACELLULAR CALCIUM IN IN-VITRO UPTAKE AND INTRAPHAGOCYTIC LOCATION OF MACROLIDES, Antimicrobial agents and chemotherapy, 39(8), 1995, pp. 1676-1682
We compared the uptakes and intracellular locations of four 14-membere
d-ring macrolides (roxithromycin, dirithromycin, erythromycin, and ery
thromycylamine) 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 mark
ed than the intracellular trapping of the other drugs (erythromycylami
ne, 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 sign
ificantly impaired, by about 50% (PMN) and 90% (cytoplasts), Furthermo
re, inorganic Ca2+ channel blockers inhibited macrolide uptake in a co
ncentration-dependent manner, with 50% inhibitory concentrations of 1.
6 to 2.0 mM and 29 to 35 mu M, respectively, for Ni2+ and La3+. The in
tracellular distributions of the drugs were unchanged in the presence
of Ni2+ and La3+ and in Ca2+-free medium supplemented with ethylene gl
ycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. The organi
c Ca2+ channel blocker nifedipine had no effect on macrolide uptake, w
hereas verapamil inhibited it in a time- and concentration-dependent m
anner. These data show the importance of extracellular Ca2+ in macroli
de uptake by phagocytes and suggest a link with Ca2+ channels or a Ca2
+ channel-operated mechanism.