ATP triggers intracellular Ca2+ release in type II cells of the rat carotid body.
Using a Ca2+-imaging technique, we studied the action of ATP on the intracellular Ca2+ concentration ([Ca2+]i) of fura-2-loaded mixtures of type I and type II cells dissociated from rat carotid bodies. ATP (100 micro M) triggered a transient rise in [Ca2+]i in the spindle-shaped type II (sustentacular) cells, but not the ovoid type I (glomus) cells. When challenged with ionomycin (1 micro M), no amperometry signal could be detected from the ATP-responsive type II cells, suggesting that these cells lacked catecholamine-containing granules. In contrast, KCl depolarization triggered robust quantal catecholamine release from type I cells that were not responsive to ATP. In type II cells voltage clamped at -70 mV, the ATP-induced [Ca2+]i rise was not accompanied by any current change, suggesting that P2X receptors are not involved. The ATP-induced Ca2+ signal could be observed in the presence of Ni2+ (a blocker of voltage-gated Ca2+ channels) or in the absence of extracellular Ca2+, indicating that Ca2+ release from intracellular stores was the dominant mechanism. The order of purinoreceptor agonist potency in triggering the [Ca2+]i rise was UTP > ATP > 2-methylthioATP >> alpha,beta-methyleneATP, implicating the involvement of P2Y2 receptors. In carotid body sections, immunofluorescence revealed localization of P2Y2 receptors on spindle-shaped type II cells that partially enveloped ovoid type I cells. Since ATP is released from type I cells during hypoxia, we suggest that the ATP-induced Ca2+ signal in type II cells can mediate paracrine interactions within the carotid bodies.
Department of Pharmacology, 9-70 Medical Science Building, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Jianhua
J
Xu
Frederick W
FW
Tse
Amy
A
Tse
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects; D002344:Carotid Body / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism; D002469:Cell Separation; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000378:metabolism; D004594:Electrophysiology; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D018048:Receptors, Purinergic P2 / Q000187:drug effects; D058473:Receptors, Purinergic P2Y2; D009418:S100 Proteins / Q000096:biosynthesis; D013268:Stimulation, Chemical
D015220:Calcium Channels; D002395:Catecholamines; C546387:P2ry2 protein, rat; D018048:Receptors, Purinergic P2; D058473:Receptors, Purinergic P2Y2; D009418:S100 Proteins; D000255:Adenosine Triphosphate; D002118:Calcium