SINGLE K+ CHANNELS IN MEMBRANE PATCHES OF ARTERIAL CHEMORECEPTOR CELLS ARE MODULATED BY O2 TENSION

Type I cells of the carotid body are known to participate in the detection of O2 tension in arterial blood but the primary chemotransduction mechanisms are not well understood. Here we report the existence in excised membrane patches of type I cells of a single K+ channel type modulated by changes in PO2. Open probability of the O2-sensitive K+ channel reversibly decreased by at least 50% on exposure to hypoxia but single-channel conductance (almost-equal-to 20 pS) was unaltered. In the range between 70 and 150 mmHg (1 mmHg = 133 Pa) the decrease of single-channel open probability was proportional to the PO2 measured in the vicinity of the membrane patch. The inhibition of K+ channel activity by low PO2 was independent of the presence of non-hydrolyzable guanine triphosphate analogues at the internal face of the membrane. The results indicate that the O2 sensor of type I cells is in the plasma membrane and suggest that environmental O2 interacts directly with the K+ channels.