Immunohistochemical distribution of extracellular signal-regulated kinase 1 and 2 (ERK1/2) in the rat carotid body

The sensitivity of the carotid body to hypoxic stimuli is enhanced by chronic intermittent hypoxia. Since extracellular signal-regulated kinase 1/2 (ERK1/2) may be involved in hypoxic responses and in sensory nerve facilitation induced by intermittent hypoxic stimuli, we examined the distribution of ERK1/2 in male Wistar rat carotid body. The results of RT-PCR and immunoblotting indicated that ERK1 and ERK2 were both expressed in the carotid body at the mRNA and protein levels. Immunoblotting also detected intense bands for phosphorylated ERK1 in the carotid body. Immunoreactivity for ERK1/2 was ubiquitously distributed in chemoreceptor cell clusters. Immunoreactivity for phosphorylated ERK1/2 (pERK1/2) was intense in some vesicular nucleotide transporter-immunoreactive chemoreceptor cells and in most P2X₂ purinoceptor-immunoreactive sensory nerve endings. In addition, pERK1/2 localization to the nuclei of chemoreceptor cells and sustentacular cells was observed. Immunoreactivity for pERK1/2 was intense in the vesicular glutamate transporter 2-immunoreactive areas of sensory nerve endings. These results suggest that ERK1/2 regulate hypoxic responses and sensitivity through the phosphorylation of their substrates in chemoreceptor cells and sensory nerve endings. ERK1/2 may be involved in transmission and sensory nerve facilitation in chemoreceptor cells and sensory nerve endings.