Figure 3. Rp‐cAMPS and PKI inhibit cAMP‐dependent upregulation of I _Ba .

A and B, effects of PKA blockers on CFTR. Oocytes expressing the CFTR channel were used without any pretreatment or pre‐injected with 50 nl of H₂O, Rp‐cAMPS (2 mm) (A) or PKI (B). Oocytes were held at −80 mV and currents were evoked in ND96 solution by injection of cAMP (200 μm). Left, averaged evoked CFTR currents following cAMP injection. Right, representative time course of current changes after cAMP injection. The experiments are from a representative batch of oocytes, out of 3. C and D, effects of PKA blockers on Ca_V1.2Δ1821. Oocytes expressing Ca_V1.2Δ1821 were used without pretreatment or pre‐injected with H₂O, Rp‐cAMPS (2 mm) (C) or PKI (D). Following pre‐injection, cAMP (200 μm)‐dependent changes in I _Ba were recorded as in Fig. 1. Averaged % increase in I _Ba per oocyte, following cAMP injection (from 3 experiments) is shown in a; representative time courses of currents following cAMP injection are shown in b. In the set of experiments with Rp‐cAMPS, the cAMP‐induced increase in Ca_V1.2Δ1821 I _Ba was relatively low (22.5% in the control group, less than the average 35.7% summarized from all experiments in Fig. 1 F), which could reflect low endogenous PKA levels or a high basal phosphorylation of the channel. Statistical significance was determined using one‐way ANOVA followed by Bonferroni test, except Da where a t test was applied. ^*** P < 0.001.