1 P1 purinoceptor agonists like adenosine have been shown to stimulate Cl-transport in secretory epithelia. In the present study, we investigated whether P1 agonist-induced Cl-secretion is preserved in cystic fibrosis airway epithelium and which signalling mechanism is involved. The effects of purinoceptor agonists on Cl-secretion were examined in a transformed cystic fibrosis airway phenotype epithelial cell line, CFPEo-. 2 Addition of adenosine (ADO; 0.1-1 mM) markedly increased 1251 efflux rate. The rank order of potency of purinoceptor agonists in stimulating 1251I efflux was ADO>AMP>ADP-ATP. A similar order of potency was seen in transformed cystic fibrosis nasal polyp cells, CFNPEo-(ADO>ATP > AMP> ADP). These results are consistent with the activation of Cl-secretion via a P1 purinoceptor. 3 The P1 agonists tested (at 0.01 and 0.1 mM) revealed a rank order of potency of 5'-Nethylcarboxamine adenosine (NECA)>2-chloro-adenosine (2-Cl-ADO)>R-phenylisopropyl adenosine (R-PIA). 4 The known potent A2 adenosine receptor (A2AR) agonist, 5'-(N-cyclopropyl) carboxamidoadenosine (CPCA, 2 JiM) but not the A1 adenosine receptor agonist, N6-phenyl adenosine (N6-phenyl ADO, 10 ELM) markedly increased 1251 efflux rate (baseline, 5.9 ± 2.0% min-', + CPCA, 10.9 ± 0.6% min-'; P<0.01). The stimulant effect of CPCA (10 gLM) was abolished by addition of the A2AR antagonist 3,7-dimethyl-1-propargylxanthine (DMPX) (100 ,.m; reported Ki = 11 ± 3 fiM). These results favour the involvement of A2AR. 6 In patch-clamp experiments, ADO (1 mM) induced an outwardly-rectified whole-cell Cl-current (baseline, 2.5 ± 0.8 pA pF-, + ADO, 78.4 ± 23.8 pA pF-'; P<0.02), which was largely inhibited in cells internally perfused with a selective inhibitory peptide of the multifunctional Ca2+/calmodulindependent protein kinase, CaMK (20 gM), as compared to a control peptide, CaMK [284][285][286][287][288][289][290][291][292][293][294][295][296][297][298][299][300][301][302]. Addition of BAPTA (10 mM), a Ca2+ chelator, to the perfusion pipette also abolished the ADO-elicited Cl-current. 7 In conclusion, our results suggest that A2AR participates in regulation of airway C1 secretion via a Ca2+-dependent signalling pathway, which involves CaMK and appears to be at least partially conserved in cystic fibrosis airway epithelial cells.