REGULATION OF THE MOUSE RETINAL TAURINE TRANSPORTER (TAUT) BY PROTEIN-KINASES IN XENOPUS OOCYTES

The goal was to investigate the role of protein kinases in modulating taurine transporter activity in Xenopus laevis oocytes expressing the mouse retinal Na+/C-/taurine transporter. The currents generated by th e taurine transporter were studied with a two-electrode voltage clamp and we recorded the maximal current (I-max), presteady-state charge tr ansfer Q, and membrane capacitance C-m. 8-Br-cAMP, a membrane-permeabl e activator of the cAMP-dependent protein kinase (PKA), decreased I-ma x (41%), Q (41%) and C-m (10%), Similarly, 1 mu M sn-1,2-dioctanoylgly cerol (DOG), an activator of the Ca2+/diacylglycerol-dependent protein kinase (PKC), decreased I-max (56%), Q (37%), and C-m (9%), Calyculin A, a specific inhibitor of protein phosphatases 1 and 2A, also produc ed effects similar to those of 8-Br-cAMP and DOG, and decreased I-max (64%), Q (38%), and C-m (10%), We conclude that the taurine transporte r is regulated by activators of PKA and PKC, and regulation occurs lar gely by changes in the number of transporters in the plasma membrane.