Secretory responses of intact glomus cells in thin slices of rat carotid body to hypoxia and tetraethylammonium.
We have developed a thin-slice preparation of whole rat carotid body that allows us to perform patch-clamp recording of membrane ionic currents and to monitor catecholamine secretion by amperometry in single glomus cells under direct visual control. In normoxic conditions (P(O(2)) approximately 140 mmHg; 1 mmHg = 133 Pa), most glomus cells did not have measurable secretory activity, but exposure to hypoxia (P(O(2)) approximately 20 mmHg) elicited the appearance of a large number of spike-like exocytotic events. This neurosecretory response to hypoxia was fully reversible and required extracellular Ca(2+) influx. The average charge of single quantal events was 46 +/- 25 fC (n = 218), which yields an estimate of approximately 140,000 catecholamine molecules per vesicle. Addition of tetraethylammonium (TEA; 2-5 mM) to the extracellular solution induced in most (>95%) cells tested (n = 32) a secretory response similar to that elicited by low P(O(2)). Cells nonresponsive to hypoxia but activated by exposure to high external K(+) were also stimulated by TEA. A secretory response similar to the responses to hypoxia and TEA was also observed after treatment of the cells with iberiotoxin to block selectively Ca(2+)- and voltage-activated maxi-K(+) channels. Our data further show that membrane ion channels are critically involved in sensory transduction in the carotid body. We also show that in intact glomus cells inhibition of voltage-dependent K(+) channels can contribute to initiation of the secretory response to low P(O(2)).
Pardal
R
R
Departamento de Fisiologia, Facultad de Medicina y Hospital Universitario Virgen del Rocio, Universidad de Sevilla, E-41009, Sevilla, Spain.
Ludewig
U
U
Garcia-Hirschfeld
J
J
Lopez-Barneo
J
J
D000818:Animals; D002344:Carotid Body / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D015687:Cell Hypoxia; D004594:Electrophysiology; D008867:Microtomy; D026902:Potassium Channel Blockers; D051381:Rats; D017208:Rats, Wistar; D019789:Tetraethylammonium / Q000494:pharmacology*
D026902:Potassium Channel Blockers; D019789:Tetraethylammonium