HYPOXIC INHIBITION OF K-I CAROTID-BODY CELLS - EVIDENCE AGAINST THE INVOLVEMENT OF CYCLIC-NUCLEOTIDES( CURRENTS IN ISOLATED RAT TYPE)

Whole-cell patch-clamp recordings were used to evaluate the effects of the cyclic nucleotides adenosine 3',5'-cyclic monophosphate (cAMP) an d guanosine 3',5'-cyclic monophosphate (cGMP) on ionic currents in typ e I carotid body cells isolated from rat pups, and to investigate whet her cyclic nucleotides are involved in K+ current inhibition by hypoxi a. In the presence of 500 mu M isobutylmethylxanthine, currents were n ot significantly modified by 8-bromo-cAMP (2 mM), dibutyryl-cAMP (5 mM ) or 8-bromo-cGMP (2 mM). Currents were also unaffected by the phospho diesterase (PDE)-resistant protein kinase A activators Sp-cyclic adeno sine-3',5'-monophosphorothioate (Sp-cAMPS) and Sp-8-bromoadenosine-3', 5'-monophosphorothioate (Sp-8-bromo-cAMPS) (50 mu M), or by beta-pheny l-1,N-2-ethenoguanosine-3',5'-cyclic monophosphate (PET-cGMP) (100 mu M) or the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP; 50 0 mu M). Ca2+ channel currents were also unaffected by Sp-8-Br-cAMPS, PET-cGMP and SNAP at the same concentrations. In the absence of cyclic nucleotide analogues, hypoxia (P-O2 17-23 mmHg) reversibly inhibited K+ currents. This degree of hypoxic inhibition was not significantly a ltered by the PDE-resistant protein kinase A inhibitors Rp-cyclic aden osine-3',5'-monophosphorothioate (Rp-cAMPS) (50 mu M) or Rp-8-bromoade nosine 3',5'-monophosphorothioate (Rp-8-bromo-cAMPS) (200 mu M). Simil arly, PET-cGMP (100 mu M) and SNAP (500 mu M) did not alter the degree of inhibition caused by hypoxia. At the same concentrations used in t ype I cell experiments, Sp-8-bromo-cAMPS, PET-cGMP and SNAP completely relaxed isolated guinea-pig basilar arteries preconstricted with 20 m M K+-containing solutions. Our results indicate that cyclic nucleotide s alone are not an important factor in the regulation by O-2 tension o f K+ currents in rat type I carotid body cells.