Hypoxia induces voltage-dependent Ca2+ entry and quantal dopamine secretion in carotid body glomus cells.
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 O2 tension (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 approximately 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 Po2 results in Ca2+ entry through voltage-gated channels, which leads to an increase in intracellular [Ca2+] and exocytotic transmitter release.
Ureña
J
J
Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, Facultad de Medicina, Spain.
Fernández-Chacón
R
R
Benot
A R
AR
Alvarez de Toledo
G A
GA
López-Barneo
J
J
D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D019256:Cadmium Chloride; D002118:Calcium / Q000378:metabolism*; D002344:Carotid Body / Q000378:metabolism / Q000502:physiology*; D015687:Cell Hypoxia; D002628:Chemoreceptor Cells / Q000187:drug effects / Q000502:physiology; D002712:Chlorides / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism* / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000031:analogs & derivatives; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009532:Nickel / Q000494:pharmacology; D010100:Oxygen / Q000494:pharmacology; D010313:Partial Pressure; D011189:Potassium Chloride / Q000494:pharmacology; D011817:Rabbits; D013997:Time Factors
D002712:Chlorides; D005456:Fluorescent Dyes; D002104:Cadmium; C049925:fura-2-am; D011189:Potassium Chloride; C022838:nickel chloride; D009532:Nickel; D019256:Cadmium Chloride; D010100:Oxygen; D002118:Calcium; D016257:Fura-2; D004298:Dopamine