Effects of hypoxia on potassium channel activities of arterial chemoreceptor cells

A current hypothesis states that oxygen-sensitive K{dollar}sp+{dollar} channels of carotid body cells play a major role in the hypoxic chemotransduction. However, the electrophysiological properties of these K{dollar}sp+{dollar} channels appear to be different among species. Little is known about the K{dollar}sp+{dollar} channel activities of cat carotid body cells, and yet the physiological behavior of the carotid body has been well studied in adult cats. The aims of this thesis research were to identify and localize oxygen-sensitive K{dollar}sp+{dollar} channels and to correlate activities of these channels with membrane potentials in the primary cultured cells of adult cat carotid body. The patch clamp technique (whole cell configuration) was applied in all studies to measure K{dollar}sp+{dollar} currents. In the first study, K{dollar}sp+{dollar} currents were recorded in carotid body cells at normoxic (PO{dollar}sb2{dollar} = 152 mmHg) and hypoxic (PO{dollar}sb2{dollar} = 25 mmHg) conditions to test the effect of hypoxia on K{dollar}sp+{dollar} channels. Some cells possessed voltage-gated oxygen-sensitive K{dollar}sp+{dollar} channels. In these cells the outward K{dollar}sp+{dollar} currents were depressed by 22% at positive test voltages during hypoxia. Other cells contained voltage-gated K{dollar}sp+{dollar} channels, that were not sensitive to oxygen. In the second study, localization of oxygen-sensitive K{dollar}sp+{dollar} channels was determined using a combination of patch clamp and immunocytochemical techniques. Anti-tyrosine hydroxylase (TH) antibody was used for identification of type I cells, and anti-glial fibrillary acidic protein (GFAP) antibody for type II cells. Cells that expressed oxygen-sensitive K{dollar}sp+{dollar} channels contained TH (7/7) but not GFAP (4/4). Cells that expressed oxygen-insensitive K{dollar}sp+{dollar} channels contained GFAP (5/5). Most of them did not contain TH (4/5). In the third study, a combination of voltage clamp and current clamp techniques was used. Membrane potentials of cells which expressed oxygen-sensitive K{dollar}sp+{dollar} channels were changed from {dollar}-{dollar}54.7 mV during normoxia to {dollar}-{dollar}26.9 mV during hypoxia. Cells which expressed oxygen-insensitive K{dollar}sp+{dollar} channels were not significantly depolarized during hypoxia. These results suggest: (1) Characteristics of K{dollar}sp+{dollar} channels in cultured cat carotid body cells are heterogenous; (2) Cells that express oxygen-sensitive K{dollar}sp+{dollar} channels are type I cells; (3) Most cells that possess oxygen-insensitive K channels are type II cells. (4) Type I cells were depolarized during hypoxia, but type II cells were not. (5) Inhibition of oxygen-sensitive K{dollar}sp+{dollar} channels may depolarize type I cells during hypoxia.