title: Effects of low glucose on carotid body chemoreceptor cell activity studied in cultures of intact organs and in dissociated cells.
abstract: The participation of the carotid body (CB) in glucose homeostasis and evidence obtained in simplified cultured CB slices or dissociated cells have led to the proposal that CB chemoreceptor cells are glucoreceptors. However, data generated in intact, freshly excised organs deny CB chemoreceptor cells' glucosensing properties. The physiological significance of the contention has prompted the present study, performed in a newly developed preparation of the intact CB organ in culture that maintains chemoreceptor cells' microenvironment. Chemoreceptor cells of intact CBs in culture retained their capacity to store, synthesize, and secrete catecholamine in response to hypoxia for at least 6 days. Aglycemia did not elicit neurosecretion in dissociated chemoreceptor cells or in intact CB in culture, but potentiated hypoxia-elicited neurosecretion, exclusively, in 1-day-old intact CB cultures and dissociated chemoreceptor cells cultured for 24 h. In fura 2-loaded cells, aglycemia (but not 1 mM) caused a slow Ca(2+)-dependent and nifedipine-insensitive increase in fluorescence at 340- to 380-nm wavelength emission ratio and augmented the fluorescent signal elicited by hypoxia. Association of nifedipine and KBR7943 (a Na(+)/Ca(2+) exchanger inhibitor) completely abolished the aglycemic Ca(2+) response. We conclude that chemoreceptor cells are not sensitive to hypoglycemia. We hypothesize that cultured chemoreceptor cells become transiently more dependent on glycolysis. Consequently, aglycemia would partially inhibit the Na(+)/K(+) pump, causing an increase in intracellular Na(+) concentration, and a reversal of Na(+)/Ca(2+) exchanger. This would slowly increase intracellular Ca(2+) concentration and cause the potentiation of the hypoxic responses. We discuss the nature of the signals detected by chemoreceptor cells for the CB to achieve its glycemic homeostatic role.
authors.affiliation: Departamento de Bioquímica y Biología Molecular y Fisiología, Instituto de Biología y Genética Molecular y Centro de Investigación Biomédica en Red de Enfermedades Respiratorias, Universidad de Valladolid, Spain.
authors.forename: Teresa
authors.initials: T
authors.lastname: Gallego-Martin
authors.forename: Silvia
authors.initials: S
authors.lastname: Fernandez-Martinez
authors.forename: Ricardo
authors.initials: R
authors.lastname: Rigual
authors.forename: Ana
authors.initials: A
authors.lastname: Obeso
authors.forename: Constancio
authors.initials: C
authors.lastname: Gonzalez
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002344:Carotid Body / Q000187:drug effects / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism; D018929:Cell Culture Techniques; D015687:Cell Hypoxia / Q000187:drug effects / Q000502:physiology; D002628:Chemoreceptor Cells / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D005947:Glucose / Q000172:deficiency* / Q000494:pharmacology*; D006019:Glycolysis; D007003:Hypoglycemia / Q000378:metabolism; D007150:Immunohistochemistry; D008297:Male; D009543:Nifedipine / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000378:metabolism; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D002395:Catecholamines; D019831:Sodium-Calcium Exchanger; D013890:Thiourea; D009543:Nifedipine; D005947:Glucose; D011188:Potassium; D002118:Calcium