Calcium-activated chloride conductance in frog olfactory cilia.
We have measured the effects of cytoplasmic Ca2+ on the conductance of single cilia excised from frog olfactory receptor neurons. When free cytoplasmic Ca2+ is buffered at 0.1 microM, ciliary conductance is low. As Ca2+ is increased, ciliary conductance increases. Maximal conductance averages sevenfold higher than that measured in the absence of Ca2+. We estimate that the K1/2 for Ca2+ activation is 5 microM; the dose-response curve indicates some positive cooperativity of Ca2+ binding. Activation by Ca2+ is rapid and fully reversible. Most of the Ca(2+)-activated current is carried by Cl- and persists in the absence of Na+ and K+. The Cl- channel inhibitor 3',5-dichlorodiphenylamine-2-carboxylate (300 microM) reduces the Ca(2+)-activated current by 90%. Odorants induce a Ca2+ influx in some olfactory receptor neurons, but the consequences of this influx for neuronal function are not well understood. Our findings allow us to predict that a Ca2+ influx would increase the permeability of the olfactory cilia to Cl-. How this would affect the neuronal potential is uncertain, since the equilibrium potential for Cl- in olfactory receptor neurons is unknown.
Department of Anatomy and Cell Biology, University of Cincinnati, Ohio 45267-0521.
S J
SJ
Kleene
R C
RC
Gesteland
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002712:Chlorides / Q000502:physiology*; D002923:Cilia / Q000502:physiology; D003593:Cytoplasm / Q000378:metabolism; D004553:Electric Conductivity; D009474:Neurons / Q000502:physiology*; D009831:Olfactory Mucosa / Q000166:cytology / Q000502:physiology*; D011188:Potassium / Q000502:physiology; D011894:Rana pipiens / Q000502:physiology*; D012964:Sodium / Q000502:physiology
D002712:Chlorides; D012964:Sodium; D011188:Potassium; D002118:Calcium