Ryanodine receptor-mediated [Ca2+](i) release in glomus cells is independent of natural stimuli and does not participate in the chemosensory responses of the rat carotid body

\The hypothesis that intracellular calcium ([Ca (2+)]) release in glomus ce lls via ryanodine receptor (RyR) activation by caffeine may be independent of natural stimuli and chemosensory discharge was tested in the rat carotid body (CB). CB type I cells were isolated, plated and preloaded with calciu m-sensitive fluorescent probe, Indo-1AM. With the increase of caffeine dose (0-50 mM) cytosolic calcium ([Ca2+](c)) increased from 85 +/- 15 nM to 193 3 +/- 190 nM (n=6) at normoxia (Po-2=125-130 Torr, Pco(2)=25-30 Torr, pH 7. 30-7.35). Hypoxia (Po-2=10-15 Torr) increased and hypocapnia (Pco(2)=7-9 To rr) decreased the cytoplasmic calcium [Ca2+](c) levels, independent 2+] ([C ' 2+]), of caffeine. Caffeine-related [Ca increase was the same in the pres ence and the absence of extracellular calcium a indicating the source of Ca 2+ ions is the cellular store. Permeabilization of the cell membrane with s aponin (25 mug/ml) retained the caffeine response. Additional treatment of the cells with 50 LM ryanodine (an inhibitor of the caffeine-activated RyR site) abolished caffeine-stimulated response. In vitro CB chemosensory (car otid sinus nerve, CSN) responses to hypoxia (Po-2=35-40 Torr) were not alte red by caffeine. These results suggest that [Ca2+](i) stores in CB cells, m obilized by RyR activation, do not participate in the CSN responses to natu ral stimuli. (C) 2001 Elsevier Science BY All rights reserved.