Intracellular Ca(2+) stores in chemoreceptor cells of the rabbit carotid body: significance for chemoreception.
The notion that intracellular Ca(2+) (Ca(i)(2+)) stores play a significant role in the chemoreception process in chemoreceptor cells of the carotid body (CB) appears in the literature in a recurrent manner. However, the structural identity of the Ca(2+) stores and their real significance in the function of chemoreceptor cells are unknown. To assess the functional significance of Ca(i)(2+) stores in chemoreceptor cells, we have monitored 1) the release of catecholamines (CA) from the cells using an in vitro preparation of intact rabbit CB and 2) the intracellular Ca(2+) concentration ([Ca(2+)](i)) using isolated chemoreceptor cells; both parameters were measured in the absence or the presence of agents interfering with the storage of Ca(2+). We found that threshold [Ca(2+)](i) for high extracellular K(+) (K(e)(+)) to elicit a release response is approximately 250 nM. Caffeine (10-40 mM), ryanodine (0.5 microM), thapsigargin (0.05-1 microM), and cyclopiazonic acid (10 microM) did not alter the basal or the stimulus (hypoxia, high K(e)(+))-induced release of CA. The same agents produced Ca(i)(2+) transients of amplitude below secretory threshold; ryanodine (0.5 microM), thapsigargin (1 microM), and cyclopiazonic acid (10 microM) did not alter the magnitude or time course of the Ca(i)(2+) responses elicited by high K(e)(+). Several potential activators of the phospholipase C system (bethanechol, ATP, and bradykinin), and thereby of inositol 1,4,5-trisphosphate receptors, produced minimal or no changes in [Ca(2+)](i) and did not affect the basal release of CA. It is concluded that, in the rabbit CB chemoreceptor cells, Ca(i)(2+) stores do not play a significant role in the instant-to-instant chemoreception process.
Vicario
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I
Departamento de Bioquímica y Biología Molecular y Fisiología, Instituto de Biología y Genética Molecular and Facultad de Medicina, Universidad de Valladolid, 47005 Valladolid, Spain.
Obeso
A
A
Rocher
A
A
López-Lopez
J R
JR
González
C
C
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002344:Carotid Body / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism; D015687:Cell Hypoxia / Q000502:physiology; D002469:Cell Separation; D002628:Chemoreceptor Cells / Q000378:metabolism* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism*; D011188:Potassium / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology; D011817:Rabbits; D012433:Ryanodine / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism
D002395:Catecholamines; D004791:Enzyme Inhibitors; D012433:Ryanodine; D002110:Caffeine; D019284:Thapsigargin; D010738:Type C Phospholipases; D011188:Potassium; D002118:Calcium