Hypoxic inhibition of Kcurrents in isolated rat type I carotid body cells: evidence against the involvement of cyclic nucleotides.

Whole-cell patch-clamp recordings were used to evaluate the effects of the cyclic nucleotides adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) on ionic currents in type I carotid body cells isolated from rat pups, and to investigate whether cyclic nucleotides are involved in Kcurrent inhibition by hypoxia. In the presence of 500 μM isobutylmethylxanthine, currents were not significantly modified by 8-bromo-cAMP (2 mM), dibutyryl-cAMP (5 mM) or 8-bromo-cGMP (2 mM). Currents were also unaffected by the phosphodiesterase (PDE)-resistant protein kinase A activators Sp-cyclic adenosine-3′,5′-monophosphorothioate (Sp-cAMPS) and Sp-8-bromoadenosine-3′,5′-monophosphorothioate (Sp-8-bromo-cAMPS) (50 μM), or by β-phenyl-1, N-ethenoguanosine-3′,5′-cyclic monophosphate (PET-cGMP) (100 μM) or the nitric oxide donor S-nitroso- N-acetylpenicillamine (SNAP; 500 μM). Cachannel 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 (P17-23 mmHg) reversibly inhibited Kcurrents. This degree of hypoxic inhibition was not significantly altered by the PDE-resistant protein kinase A inhibitors Rp-cyclic adenosine-3′,5′-monophosphorothioate (Rp-cAMPS) (50 μM) or Rp-8-bromoadenosine-3′,5′-monophosphorothioate (Rp-8-bromo-cAMPS) (200 μM). Similarly, PET-cGMP (100 μM) and SNAP (500 μM) did not alter the degree of inhibition caused by hypoxia. At the same concentrations used in type I cell experiments, Sp-8-bromo-cAMPS, PET-cGMP and SNAP completely relaxed isolated guinea-pig basilar arteries preconstricted with 20 mM K-containing solutions. Our results indicate that cyclic nucleotides alone are not an important factor in the regulation by Otension of Kcurrents in rat type I carotid body cells. [ABSTRACT FROM AUTHOR]