Extracellular K+ as an Interneuronal Coupler in the Carotid Body
Recent biophysical studies in the carotid body have shown that the membrane characteristics of type I cells (TICs) and type II cells (TIICs) fit those of a neuron and a glial cell, respectively (1). Other studies have shown also that, in addition to their ability to fire action potentials, TICs respond to cyanide with an increase in K+ conductance and a reversible increase in intracellular calcium (2,3). These results suggest that a neurotransmitter is released from TICs in hypoxia, as previously demonstrated in the whole carotid body (4). As a consequence, the interest in the “neurotransmitter hypothesis” to explain the coupling between TICs and nerve endings (NEs) has been revived recently. However, the main objections to the neurotranmitter hypothesis remain since no antagonist has been found yet that blocks the carotid body response to hypoxia, nor has a neurotransmitter been shown to induce sustained afferent discharge comparable to that seen in severe hypoxia (5).
KeywordsFiring Rate Carotid Body Giant Axon Fire Action Potential Osmotic Water Flow
Unable to display preview. Download preview PDF.
- 2.Biscoe TJ, Duchen MR, Kirby GC, Patterson DL, Ponte J. (1988). Voltage clamp study of the effects of cyanide on dissociated type I cells of the rabbit carotid body. J Physiol (Lond) 396: 178 P.Google Scholar
- 3.Biscoe TJ, Duchen MR, Eisner DA, O’Neill SC, Valdeolmillos M (1988). Cyanide increases [Ca2+], in isolated type I cells from rabbit carotid body. J Physiol (Lond) 396: 99 P.Google Scholar
- 4.Fidone S, Gonzalez C, Yoshizaki K (1982). Effects of low oxygen on the release of dopamine from the rabbit carotid body in vitro. J Physiol (Lond) 333: 93–110.Google Scholar
- 5.McQueen D (1983). Pharmacological aspects of putative transmitters in the carotid body. In: Acker H, O’Regan RG (Eds). Physiology of the Peripheral Chemoreceptors. Amsterdam: Elsevier, pp. 149–196.Google Scholar
- 6.Ferreira HG, Marshall MW (1985). The Biophysical Basis of Excitability. Cambridge University Press, Cambridge.Google Scholar
- 8.Kukita F (1988). Removal of periaxonal potassium accumulation in a squid giant axon by outward osmotic water flow. J Physiol (Lond) 399: 647–656.Google Scholar
- 10.O’Regan RG, Acker H (1987). Effects of cyanide and acetylcholine on extra-cellular K+ and Ca2+ activities in the cat carotid body. In: Ribeiro JA, Pallot DJ (Eds). Chemoreceptors in Respiratory Control, Croom Helm, London, pp. 99–107.Google Scholar