Hypoxia Induces Voltage-Dependent Ca2+Entry and Quantal Dopamine Secretion in Carotid Body Glomus Cells

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 91; no. 21; pp. 10208 - 10211
• Main Authors: Ureña, J., Fernández-Chacón, R., Benot, A. R., de Toledo, G. Alvarez, López-Barneo, J.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 11.10.1994; National Acad Sciences
• Subjects: Animals; Cadmium - pharmacology; Cadmium Chloride; Calcium - metabolism; Carotid body; Carotid Body - metabolism; Carotid Body - physiology; Cell Hypoxia; Cell membranes; Chemoreceptor Cells - drug effects; Chemoreceptor Cells - physiology; Chlorides - pharmacology; Chromaffin cells; Cytosol - metabolism; Depolarization; Dopamine - metabolism; Dopamine - pharmacology; Electric current; Electric potential; Electrodes; Fluorescent Dyes; Fura-2 - analogs & derivatives; Hypoxia; In Vitro Techniques; Kinetics; Membrane Potentials - drug effects; Nickel - pharmacology; Oxygen - pharmacology; Partial Pressure; Potassium Chloride - pharmacology; Rabbits; Secretion; Secretory vesicles; Time Factors
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.91.21.10208

We have investigated the changes of cytosolic [Ca2+] and the secretory activity in single glomus cells dispersed from rabbit carotid bodies during exposure to solutions with variable O2tension (PO2). In normoxic conditions (PO2= 145 mmHg; 1 mmHg = 133 Pa), intracellular [Ca2+] was 58 ± 29 nM, and switching to low PO2(between 10 and 60 mmHg) led to a reversible increase of [Ca2+] up to 800 nM. The response to hypoxia completely disappeared after removal of external Ca2+or with the addition of 0.2 mM Cd2+to the external solution. These same solutions also abolished both the Ca2+current of the cells and the increase of internal [Ca2+] elicited by high external K+. Elevations of cytosolic [Ca2+] in response to hypoxia or to direct membrane depolarization elicited the release of dopamine, which was detected by amperometric techniques. Dopamine secretion occurred in episodes of spike-like activity that appear to represent the release from single secretory vesicles. From the mean charge of well-resolved secretory events, we estimated the average number of dopamine molecules per vesicle to be ≈140,000, a value about 15 times smaller than a previous estimate in chromaffin granules of adrenomedullary cells. These results directly demonstrate in a single-cell preparation the secretory response of glomus cells to hypoxia. The data indicate that the enhancement of cellular excitability upon exposure to low PO2results in Ca2+entry through voltage-gated channels, which leads to an increase in intracellular [Ca2+] and exocytotic transmitter release.