Figure 3.

The entire membrane pool of R334C CFTR channels that were activated by cAMP was labeled with MTSET⁺ before the activation. Records of g_Cl versus time obtained from R334C CFTR expressing oocytes that were obtained from the same frog and assayed on the same day. Oocytes were always perfused with frog Ringer's unless noted (see materials and methods). After a control period, they were perfused with stimulatory cocktail containing 10 μM isoproterenol and 1 mM IBMX (Isop + IBMX). (A) A record of g_Cl versus time showing that at the steady-state activation, MTSET⁺ caused about a doubling of g_Cl. (B) A record of g_Cl versus time showing that the activated g_Cl at the steady state of an oocyte preexposed to MTSET⁺ was much higher than the g_Cl at unmodified condition as seen in A, and 2-ME reduced g_Cl to ∼50% of the maximum g_Cl. (C) A record of g_Cl versus time of showing that the exposure to MTSES⁻ after prelabeling with MTSET⁺ had no effect on g_Cl before and after activation.