Secretory responses of intact glomus cells in thin slices of rat carotid body to hypoxia and tetraethylammonium
|Pardal Redondo, Ricardo
García Hirschfeld, Julia
López Barneo, José
|Universidad de Sevilla. Departamento de Fisiología Médica y Biofísica
|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 ...
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 (PO2 ' 140 mmHg; 1 mmHg 5 133 Pa), most glomus cells did not have measurable secretory activity, but exposure to hypoxia (PO2 ' 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 Ca21 influx. The average charge of single quantal events was 46 6 25 fC (n 5 218), which yields an estimate of '140,000 catecholamine molecules per vesicle. Addition of tetraethylammonium (TEA; 2–5 mM) to the extracellular solution induced in most (>95%) cells tested (n 5 32) a secretory response similar to that elicited by low PO2. Cells nonresponsive to hypoxia but activated by exposure to high external K1 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 Ca21- and voltage-activated maxi-K1 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 K1 channels can contribute to initiation of the secretory response to low PO2.