Ryanodine receptor-mediated [Ca(2+)](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+)](i)) release in glomus cells 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 calcium-sensitive fluorescent probe, Indo-1AM. With the increase of caffeine dose (0-50 mM) cytosolic calcium ([Ca(2+)](c)) increased from 85+/-15 nM to 1933+/-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 Torr) decreased the cytoplasmic calcium [Ca(2+)](c) levels, independent of caffeine. Caffeine-related [Ca(2+)](c) increase was the same in the presence and the absence of extracellular calcium ([Ca(2+)](o)), indicating the source of Ca(2+) ions is the cellular store. Permeabilization of the cell membrane with saponin (25 microg/ml) retained the caffeine response. Additional treatment of the cells with 50 microM ryanodine (an inhibitor of the caffeine-activated RyR site) abolished caffeine-stimulated response. In vitro CB chemosensory (carotid sinus nerve, CSN) responses to hypoxia (PO(2)=35-40 Torr) were not altered by caffeine. These results suggest that [Ca(2+)](i) stores in CB cells, mobilized by RyR activation, do not participate in the CSN responses to natural stimuli.
Mokashi
A
A
Department of Physiology, B-400 Richards Building, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085, USA.
Roy
A
A
Rozanov
C
C
Daudu
P
P
DiGuilio
C
C
Lahiri
S
S
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002344:Carotid Body / Q000187:drug effects / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D000860:Hypoxia / Q000378:metabolism / Q000503:physiopathology; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism*; D009924:Organ Culture Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism*; D012503:Saponins / Q000494:pharmacology; D017833:Visceral Afferents / Q000187:drug effects / Q000502:physiology
D000697:Central Nervous System Stimulants; D002614:Chelating Agents; D019837:Ryanodine Receptor Calcium Release Channel; D012503:Saponins; D002110:Caffeine; D002118:Calcium