Inhibition of Na⁺, K⁺-ATPase activates swelling-induced taurine efflux in a human neuroblastoma cell line

The Na⁺ pump (Na⁺, K⁺ -ATPase) has been implicated in the regulation. The effects of inhibiting Na⁺ pump activity on cell volume and taurine efflux were 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 regulatory volume decrease (RVD). In cells treated with ouabain, ¹⁴C-taurine efflux increased by 183 ± 11% compared with controls. However, cells exposed simultaneously to ouabain and hypoosmotic solution resulted in a ¹⁴C-taurine efflux of 207 ± 18%. Western blot and immunofluorescence microscopy with specific monoclonal antibodies for the catalytic α isoforms of Na⁺, K⁺ -ATPase demonstrated high levels of the ubiquitously expressed α1 and the neuronal- specific α3. Ouabain-binding data showed that CHP-100 cells express ~3 x 10⁵ pump units/cell. The present data indicate the efflux of taurine maya be involved during volume recovery subsequent to blockade of Na⁺, K⁺ -ATPase in CHP-100 cells.