Atrial natriuretic peptide (
ANP) and its analog,
atriopeptin III (APIII), inhibit carotid body chemoreceptor nerve activity evoked by
hypoxia. In the present study, we have examined the hypothesis that the inhibitory effects of
ANP and APIII are mediated by
cyclic GMP and
protein kinase G (PKG) via the phosphorylation and/or dephosphorylation of K(+) and Ca(2+) channel
proteins that are involved in regulating the response of carotid body chemosensory type I cells to low-O(2) stimuli. In freshly dissociated rabbit type I cells, we examined the effects of a PKG inhibitor,
KT-5823, and an inhibitor of
protein phosphatase 2A (PP2A),
okadaic acid (OA), on K(+) and Ca(2+) currents. We also investigated the effects of these specific inhibitors on intracellular Ca(2+) concentration and carotid sinus nerve (CSN) activity under normoxic and hypoxic conditions. Voltage-dependent K(+) currents were depressed by
hypoxia, and this effect was significantly reduced by 100 nM APIII. The effect of APIII on this current was reversed in the presence of either 1 microM
KT-5823 or 100 nM OA. Likewise, these drugs retarded the depression of voltage-gated Ca(2+) currents induced by APIII. Furthermore, APIII depressed
hypoxia-evoked elevations of intracellular Ca(2+), an effect that was also reversed by OA and
KT-5823. Finally, CSN activity evoked by
hypoxia was decreased in the presence of 100 nM APIII, and was partially restored when APIII was presented along with 100 nM OA. These results suggest that
ANP initiates a cascade of events involving PKG and PP2A, which culminates in the dephosphorylation of K(+) and Ca(2+) channel
proteins in the chemosensory type I cells.