K+ and Ca2+ channel activity and cytosolic [Ca2+] in oxygen-sensing tissues

Ion channels are known to participate in the secretory or mechanical responses of chemoreceptor cells to changes in oxygen tension (P-O2). We review here the modifications of K+ and Ca2+ channel activity and the resulting changes in cytosolic [Ca2+] induced by low P-O2 in glomus cells and arterial smooth muscle which are well known examples of O-2-sensitive cells. Glomus cells of the carotid body behave as presynaptic-like elements where hypoxia produces a reduction of K+ conductance leading to enhanced membrane excitability, Ca2+ entry and release of dopamine and other neurotransmitters. In arterial myocytes, hypoxia can inhibit or potentiate Ca2+ channel activity, thus regulating cytosolic [Ca2+] and contraction. Ca2+ channel inhibition is observed in systemic myocytes and most conduit pulmonary myocytes, whereas potentiation is seen in a population of resistance pulmonary myocytes. The mechanism whereby O-2 modulates ion channel activity could depend on either the direct allosteric modulation by O-2-sensing molecules or redox modification by reactive chemical species. (C) 1999 Elsevier Science B.V. All rights reserved.