Time course of K+ current inhibition by low oxygen in chemoreceptor cells of adult rabbit carotid body. Effects of carbon monoxide

Abstract

Carotid body (CB) chemoreceptors respond to a decrease in arterial blood pOz with an increase in action potential frequency in the sensory fibers innervating the organ, the response developing in a few seconds [l]. Chemoreceptor cells of the CB are the Oz sensing structures, releasing neurotransmitters in proportion to the pOz decrease and producing an electrical discharge of parallel intensity in the sensory nerve fibers of the carotid sinus nerve [2,3]. Recently, it has been shown that chemoreceptor cells possess an O,-sensitive K’ current that is reversibly inhibited by decreasing pOz in the bathing solution. The suggestion was made that this inhibition can lead to cell depolarization and activation of voltage-dependent Ca” channels [4,5]; the entry of Ca”+ through these channels, that are dihydropyridinesensitive, would trigger the release of neurotransmitters [6,7]. To accept this sequence, the inhibition of the K’ current must precede the activation of the sensory nerve discharges [8], that is, the inhibition mus: develop within the initial 3 s after lowering pOz, the time elapsing between a decrease in arterial pO1! and the increase in the carotid sinus nerve action potential frequency [l]. On the other hand, the suggestion has been made that the O?-sensor in chemoreceptor cells should be a hemoglobin- like hemoprotein, but no direct evidence to support this suggestion is available [l]. The presentstudy compares the time course of the inhibition of the K’ current by low pO1 and that of Na” current inhibition by TTX, which is known to occur in a few hundred ms [SJ. I: is shown that the former inhibition is faster. It is also shown that carbon monoxide, a very inert gas that in biological systems only reacts with hemoproteins, prevents the low PO,-induced inhibition of chemorcceptor cells E;” current.