Effects of inhibition of myo-inositol transport on MDCK cells under hypertonic environment.
To investigate the role of myo-inositol under hypertonic conditions, we examined the effects of inhibition of myo-inositol transport in Madin-Darby canine kidney (MDCK) cells using an analog of myo-inositol, 2-O,C-methylene-myo-inositol (MMI). We first characterized the inhibitory effects of MMI on myo-inositol transport in MDCK cells. The Na+-dependent component of [3H] myo-inositol uptake was inhibited by MMI in a concentration-dependent manner, although MMI did not inhibit the activities of the betaine transporter and system A neutral amino acid transporter. We found decreased affinity for myo-inositol in the presence of MMI, whereas the maximal velocity (Vmax) of the transporter did not change. Thus MMI behaves as a competitive inhibitor of myo-inositol transport with a relatively high inhibition constant (K(i)) value (1.6 mM). Myo-inositol content in hypertonic MDCK cells was markedly reduced in the presence of 5 mM MMI, but MMI itself did not accumulate in these cells. The hypertonic cells began to detach in the presence of MMI 3 days after increasing medium osmolality, whereas MMI did not affect the cells in isotonic medium. We also examined the effects of MMI on colony-forming efficiency of MDCK cells. MMI decreased colony-forming efficiency in a concentration-dependent manner, and addition of myo-inositol returned the efficiency to the value without MMI. Addition of betaine also increased colony-forming efficiency in the presence of MMI. These results indicate that myo-inositol plays an important role in survival and growth under hypertonic environment.
Kitamura
H
H
First Department of Medicine, Osaka University School of Medicine, Suita, Japan.
Yamauchi
A
A
Nakanishi
T
T
Takamitsu
Y
Y
Sugiura
T
T
Akagi
A
A
Moriyama
T
T
Horio
M
M
Imai
E
E
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004285:Dogs; D006982:Hypertonic Solutions / Q000494:pharmacology*; D007294:Inositol / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D006982:Hypertonic Solutions; D007294:Inositol