Intracellular Ca stores in chemoreceptor cells of the rabbit carotid body: significance for chemoreception

Vicario, I., A. Obeso, A. Rocher, J. R. López-Lopez, and C. González. Intracellular Ca stores in chemoreceptor cells of the rabbit carotid body: significance for chemoreception. Am J Physiol Cell Physiol 279: C51–C61, 2000.—The notion that intracellular Ca (Cai ) 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 stores and their real significance in the function of chemoreceptor cells are unknown. To assess the functional significance of Cai 21 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 concentration ([Ca]i) using isolated chemoreceptor cells; both parameters were measured in the absence or the presence of agents interfering with the storage of Ca. We found that threshold [Ca]i for high extracellular K (Ke ) to elicit a release response is '250 nM. Caffeine (10–40 mM), ryanodine (0.5 mM), thapsigargin (0.05–1 mM), and cyclopiazonic acid (10 mM) did not alter the basal or the stimulus (hypoxia, high Ke )-induced release of CA. The same agents produced Cai 21 transients of amplitude below secretory threshold; ryanodine (0.5 mM), thapsigargin (1 mM), and cyclopiazonic acid (10 mM) did not alter the magnitude or time course of the Cai 21 responses elicited by high Ke . 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]i and did not affect the basal release of CA. It is concluded that, in the rabbit CB chemoreceptor cells, Cai 21 stores do not play a significant role in the instantto-instant chemoreception process.