AQUAPORIN-1 - AN OSMOINDUCIBLE WATER CHANNEL IN CULTURED MIMCD-3 CELLS

The expressions of aquaporin-1 (AQP-1) in cultured mIMCD-3 cells were studied. There was no detectable AQP-1 in cells grown in serum contain ing growth medium (SM, 297 +/- 2 mOsm/kg . H2O). When SM was supplemen ted with NaCl (406 +/- mOsm/kg . H2O), cellular AQP-1 was induced. A f urther increase in medium osmolarity with NaCl (493 +/- 3 mOsm/kg . H2 O) had conferred cells an 2.5 to 3-fold increase of AQP-1 expression o ver those grown in the 406 +/- 2 mOsm/kg . H2O medium. Moreover, AQP-1 was found to be translocated from cytosol to membrane. In addition, e xposing the mIMCD-3 cells to vasopressin (AVP, 10(-8) M) and/or NaCl-s upplemented serum-free media (496 +/- 3 mOsm/kg . H2O) for 6h did not render them to produce AQP-1. However, AQP-1 was induced after 24h of incubation, with an 1.5-fold additive effect by AVP. Our RT-PCR data h ad confirmed the NaCl inducibility and AVP synergism in AQP-1 expressi on at both mRNA and protein levels. This suggests a new role for cellu lar AQP-1 and AVP in overcoming osmotic stress in an in vitro system. (C) 1998 Academic Press.