Evidence that 5-HT stimulates intracellular Ca2+ signalling and activates pannexin-1 currents in type II cells of the rat carotid body

摘要

Carotid body (CB) chemoreceptor (type I) cells can synthesize and release 5-HT and increased autocrine-paracrine 5-HT2 receptor signalling contributes to sensory long-term facilitation during chronic intermittent hypoxia (CIH). However, recent studies suggest that adjacent glial-like type II cells can respond to CB paracrine signals by elevating intracellular calcium ([Ca2+](i)) and activating carbenoxolone-sensitive, ATP-permeable, pannexin (Panx)-1-like channels. In the present study, using dissociated rat CB cultures, we found that 5-HT induced [Ca2+](i) responses in a subpopulation of type I cells, as well as in most (approximate to 67%) type II cells identified by their sensitivity to the P2Y2 receptor agonist, UTP. The 5-HT-induced Ca2+ response in type II cells was dose-dependent (EC50 approximate to 183nm) and largely inhibited by the 5-HT2A receptor blocker, ketanserin (1m), and also arose mainly from intracellular stores. 5-HT also activated an inward current (I5-HT) in type II cells (EC50 approximate to 200nm) that was reversibly inhibited by ketanserin (1-10nm), the Ca2+ chelator BAPTA-AM (5m), and low concentrations of carbenoxolone (5m), a putative Panx-1 channel blocker. I5-HT reversed direction at approximately -11mV and was indistinguishable from the UTP-activated current (I-UTP). Consistent with a role for Panx-1 channels, I-UTP was reversibly inhibited by the specific Panx-1 mimetic peptide blocker (10)Panx (100m), although not by its scrambled control peptide ((sc)Panx). Because ATP is an excitatory CB neurotransmitter, it is possible that the contribution of enhanced 5-HT signalling to the increased sensory discharge during CIH may occur, in part, by a boosting of ATP release from type II cells via Panx-1 channels.