Developmental expression of pH‐sensitive Kir4.1 and Kir5.1 channels in serotonergic (5‐HT) neurons

Abstract

The ventilatory response to hypercapnia in rodents increases throughout postnatal development, which parallels the increases in cellular CO2/pH sensitivity of serotonergic (5-HT) neurons in primary cell cultures. Here we tested the hypothesis that age-related changes in gene expression of pH-sensitive ion channels in 5-HT neurons might contribute to the changes in cellular and/or organismal CO2/pH sensitivity. Acutely dissociated medullary raphe tissues from transgenic rats with enhanced green fluorescent protein (eGFP) expressed in Pet-1+ (5-HT) neurons (ePet-1:eGFP rats) were used for fluorescence assisted cell sorting (FACS) to isolate eGFP+ and eGFP- neuron pools from young (<P3) and adult (>P49) rats. mRNA sequencing and differential expression analyses of these cell pools identified 4198 known genes that were differentially-expressed (p < 0.01) with increasing age. Of 70 potassium ion (K+) channel genes detected, 35 were differentially expressed. 25 of 70 K+ channels, including kcnk3 (TASK-1) and kcnk9 (TASK-3), were significantly downregulated with increasing age in 5-HT neurons. In contrast, kcnj10 (Kir4.1) and kcnj16 (Kir5.1) significantly increased in expression with increasing age and exhibited 10-fold higher expression levels than all other K channel genes in mature 5-HT neurons, which was confirmed with qPCR and western blots. Given that Kir4.1 and 5.1 form a pH-sensitive heteromeric K+ channel, we propose that the expression data point to a role for Kir4.1/5.1 channels in the development of cellular CO2/pH chemosensitivity in 5-HT neurons and possibly the CO2 chemoreflex in vivo.