Vs. Toddywalla et al., ACTIVE-TRANSPORT OF NITROFURANTOIN ACROSS A MOUSE MAMMARY EPITHELIAL MONOLAYER, The Journal of pharmacology and experimental therapeutics, 280(2), 1997, pp. 669-676
The antibiotic nitrofurantoin is transported against an electrochemica
l gradient into milk.A monolayer of CIT3 cells, a subline of the Comma
1D normal mouse mammary epithelial cell line, transports [C-14]-nitro
furantoin against a concentration gradient from the basal to the apica
l solution when grown on membrane filters. In a side-by-side diffusion
chamber with well-stirred solutions on both sides, the transfer rate
is 50% higher in the basal-to-apical than in the apical-to-basal direc
tion. Nonlabeled nitrofurantoin (500 mu M) in the basal chamber equali
zed the transport in both directions, suggesting that a specific trans
porter is responsible for the basal-to-apical increment in flux. From
inhibition studies, the apparent affinity of this transporter for nitr
ofurantoin is 50 mu M. Changes in pH between 6.4 and 7.8 had no effect
on the active transport component of the flux but did affect the pass
ive flux component. Passive flux of the nonionized molecule was 2.6 ti
mes faster than that of the ionized molecule, but the ionized molecule
did appear to cross the membrane passively. Our findings show that ni
trofurantoin is actively transported across a mammary epithelial cell
monolayer by a transporter whose affinity for nitrofurantoin does not
depend on the anionic charge on nitrofurantoin. The pH dependence of a
parallel passive pathway suggests that both nonionized and ionized fo
rms of nitrofurantoin cross the membranes of the mammary epithelial ce
ll by passive diffusion.