Carbenoxolone-sensitive and cesium-permeable potassium channel in the rod cells of frog taste discs

The rod cells in frog taste discs display the outward current and maintain the negative resting potential in the condition where internal K⁺ is replaced with Cs⁺. We analyzed the properties of the Cs⁺-permeable conductance in the rod cells. The current–voltage (I/V) relationships obtained by a voltage ramp were bell-shaped under Cs⁺ internal solution. The steady state I/V relationships elicited by voltage steps also displayed the bell-shaped outward current. The activation of the current accelerated with the depolarization and the inactivation appeared at positive voltage. The gating for the current was maintained even at symmetric condition (Cs⁺ external and internal solutions). The wing cells did not show the properties. The permeability for K⁺ was a little larger than that for Cs⁺. Internal Na⁺ and NMDG⁺ could not induce the bell-shaped outward current. Carbenoxolone inhibited the bell-shaped outward Cs⁺ current dose dependently (IC₅₀: 27 μM). Internal arachidonic acid (20 μM) did not induce the linear current–voltage (I–V) relationship which is observed in two-pore domain K⁺ channel (K_2P). The results suggest that the resting membrane potentials in the rod cells are maintained by the voltage-gated K⁺ channels.