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 a llows us to perform patch-clamp recording of membrane ionic currents and to monitor catecholamine secretion by amperometry in single glomus cells unde r direct visual control. In normoxic conditions (PO2 approximate to 140 mmH g; 1 mmHg = 133 Pa), most glomus cells did not have measurable secretory ac tivity, but exposure to hypoxia (PO2 approximate to 20 mmHg) elicited the a ppearance of a large number of spike-like exocytotic events. This neurosecr etory response to hypoxia was fully reversible and required extracellular C a2+ influx. The average charge of single quantal events was 46 +/- 25 fC (n = 218), which yields an estimate of approximate to 140,000 catecholamine m olecules per vesicle. Addition of tetraethylammonium (TEA; 2-5 mM) to the e xtracellular solution induced in most (>95%) cells tested (n = 32) a secret ory response similar to that elicited by low PO2. tells nonresponsive to hy poxia 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 select ively Ca2+- and voltage-activated maxi-K+ channels. Our data further show t hat membrane ion channels are critically involved in sensory transduction i n 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 PO2.