INHIBITION OF NA-ATPASE ACTIVATES SWELLING-INDUCED TAURINE EFFLUX IN A HUMAN NEUROBLASTOMA CELL-LINE(, K+)

The Na+ pump (Na+, K+-ATPase) has been implicated in the regulation of many cellular functions, including cell volume regulation. The effect s of inhibiting Na+ pump activity on cell volume and taurine efflux we re evaluated in the human neuroblastoma cell line CHP-100. Cell volume changes monitored with the Coulter Multisizer technique and confocal microscopy showed that neuroblastoma cells exposed to ouabain swelled by 22 +/- 4% (n = 5). The rapid cell swelling was followed by regulato ry volume decrease (RVD). In cells treated with ouabain, C-14-taurine efflux increased by 183 +/- 11% compared with controls. However, cells exposed simultaneously to ouabain and hypoosmotic solution resulted i n a C-14-taurine efflux of 207 +/- 18%. Western blot and immunofluores cence microscopy with specific monoclonal antibodies for the catalytic alpha isoforms of Na+, K+-ATPase demonstrated high levels of the ubiq uitously expressed alpha 1 and the neuronal-specific alpha 3. Ouabain- binding data showed that CHP-100 cells express similar to 3 x 10(5) pu mp units/cell. The present data indicate that efflux of taurine may be involved during volume recovery subsequent to blockade of Na+, K+-ATP ase in CHP-100 cells. (C) 1998 Wiley-Liss, Inc.