Figure 2.

Stimulation of PKA by β₂AR in Xenopus oocytes. (A) Original current trace from an oocyte expressing CFTR Cl⁻ channels and β₂AR recorded at a holding potential of −80 mV in ND96 solution. Upon isoproterenol superfusion (1 μmol/liter), CFTR channels were stimulated by PKA phosphorylation, what could be reversed by washing out of the agonist. During the second application of Iso, 30 pmol Rp-cAMPS were injected into the cytosol, abolishing and reversing the effect of agonist. (B) Same as in A, but instead of the second Iso pulse, 30 pmol cAMP was injected, stimulating CFTR channels to the same extend as the Iso pulse. (C) Statistics of stimulation of CFTR by agonist and/or cAMP and analogues normalized to a first, control pulse of Iso (taken as 100%). Calculated average values ± SEM are shown; the number of individual oocytes is given in parenthesis. (***) Mean value deviates significantly (P < 0.001) level from the group injected with stimulatory cAMP analogues. (Iso) After washing out of the first Iso pulse, 5 nl H₂O were injected into the oocyte, and then the magnitude of CFTR currents elicited by a second pulse of Iso was measured. (cAMP) After the first pulse of Iso superfusion, 30–60 pmol cAMP (n = 3) or Sp-cAMPS (n = 2) were injected into the cytosol and the resulting CFTR currents were measured. (Rp-cAMPS) Same as cAMP, but Rp-cAMPS was injected instead of stimulatory cyclic nucleotides.