RECEPTORS THAT COUPLE TO 2 CLASSES OF G-PROTEINS INCREASE CAMP AND ACTIVATE CFTR EXPRESSED IN XENOPUS-OOCYTES

The cystic fibrosis transmembrane conductance regulator (CFTR), a Cl- channel activated by phosphorylation, was expressed in Xenopus ooctyes along with various combinations of several other components of the cA MP signalling pathway. Activation of the coexpressed beta2 adrenergic receptor increased cAMP and led to CFTR activation. The activation of CFTR (1) requires only short (15 s) exposure to isoproterenol, (2) occ urs for agonist concentrations 100-1000 fold lower than those that pro duce cAMP increases detectable by a radioimmunoassay, (3) requires inj ection of only 5 pg of receptor cRNA per oocyte, and (4) can be increa sed further by coexpression of cRNA for adenylyl cyclase type II or II I or for Gsa. In addition, CFTR activation and cAMP increases by beta2 activation were enhanced by activation of the coexpressed 5HT1A recep tor, which is thought to couple to Gi. The additional activation by th e 5HT1A receptor was enhanced by coexpression of adenylyl cyclase type II but not with type Ill and may proceed via the betagamma subunits o f a G protein. The sensitivity of the assay system is also demonstrate d by responses to vasoactive intestinal peptide and to pituitary adeny late cyclase-activating polypeptide in oocytes injected with cerebral cortex mRNA.