Regulation of the mouse retinal taurine transporter (TAUT) by protein kinases in Xenopus oocytes

Abstract

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 the taurine transporter were studied with a two-electrode voltage clamp and we recorded the maximal current (I _max ), presteady-state charge transfer Q, and membrane capacitance C _m . 8-BR-cAMP, a membrane-permeable activator of the cAMP-dependent protein kinase (PKA), decreased I _max (41%), Q (41%) and C _m (10%). Similarly, 1 μM sn-1,2-dioctanoylglycerol (DOG), an activator of the Ca²⁺ I 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 produced 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 transporter is regulated by activators of PKA and PKC, and regulation occurs largely by changes in the number of transporters in the plasma membrane.