P(O(2))-P(CO(2)) stimulus interaction in [Ca(2+)](i) and CSN activity in the adult rat carotid body.
Since glomus cell intracellular calcium ([Ca(2+)](i)) plays a key role in generating carotid sinus nerve (CSN) discharge, we hypothesized that glomus cell [Ca(2+)](i) would correspond to CSN discharge rates during P(O(2))-P(CO(2)) stimulus interaction in adult rat carotid body (CB). Accordingly, we measured steady state P(O(2))-P(CO(2)) interaction in CSN discharge rates during hypocapnia (P(CO(2))=8-10 Torr), normocapnia (P(CO(2))=33-35 Torr) and hypercapnia (P(CO(2))=68-70 Torr) in normoxia (P(O(2)) approximately 130 Torr) and hypoxia (P(O(2)) approximately 36 Torr). The results showed P(O(2))-P(CO(2)) stimulus interaction in CSN responses. [Ca(2+)](i) levels were measured in isolated type I cells (2-3 cells/field), using Ca(2+) sensitive fluoroprobe indo-1AM. The [Ca(2+)](i) responses increased with increasing P(CO(2)) in normoxia. In hypoxia, [Ca(2+)](i) did not increase during hypocapnia but increased during normocapnia, showing P(O(2))-P(CO(2)) interaction. However, CSN response during hypoxia was far greater than that for [Ca(2+)](i) response, particularly during hypocapnic hypoxia. Thus, the [Ca(2+)](i) interaction cannot account for the whole CSN interaction. The origin of this CSN P(O(2)-)P(CO(2)) interaction must have occurred in part beyond cellular [Ca(2+)](i) interaction. Interactions at both sites (glomus cell membrane and sinus nerve endings) are reminiscent of reversible O(2)-heme protein reaction with a Bohr effect.
Department of Physiology, University of Pennsylvania School of Medicine, B-400 Richards Building, Philadelphia, PA 19104-6085, USA.
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Roy
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Rozanov
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Mokashi
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Lahiri
D000818:Animals; D001016:Aortic Bodies / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002245:Carbon Dioxide / Q000032:analysis; D002346:Carotid Sinus / Q000294:innervation* / Q000503:physiopathology; D006935:Hypercapnia / Q000503:physiopathology; D016857:Hypocapnia / Q000503:physiopathology; D000860:Hypoxia / Q000503:physiopathology; D008297:Male; D010100:Oxygen / Q000032:analysis; D010313:Partial Pressure; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D002245:Carbon Dioxide; D010100:Oxygen; D002118:Calcium