Contribution of cyclic-nucleotide-gated channels to the resting conductance of olfactory receptor neurons.
The basal conductance of unstimulated frog olfactory receptor neurons was investigated using whole-cell and perforated-patch recording. The input conductance, measured between -80 mV and -60 mV, averaged 0.25 nS in physiological saline. Studies were conducted to determine whether part of the input conductance is due to gating of neuronal cyclic-nucleotide-gated (CNG) channels. In support of this idea, the neuronal resting conductance was reduced by each of five treatments that reduce current through CNG channels: external application of divalent cations or amiloride; treatment with either of two adenylate cyclase inhibitors; and application of AMP-PNP, a competitive substrate for adenylate cyclase. The current blocked by divalent cations or by a cyclase inhibitor reversed near 0 mV, as expected for a CNG current. Under physiological conditions, gating of CNG channels contributes approximately 0.06 nS to the resting neuronal conductance. This implies a resting cAMP concentration of 0.1-0.3 micro M. A theoretical model suggests that a neuron containing 0.1-0.3 micro M cAMP is poised to give the largest possible depolarization in response to a very small olfactory stimulus. Although having CNG channels open at rest decreases the voltage change resulting from a given receptor current, it more substantially increases the receptor current resulting from a given increase in [cAMP].
Pun
Raymund Y K
RY
Department of Molecular and Cellular Physiology, University of Cincinnati, PO Box 670576, Cincinnati, OH 45267, USA. raymund.pun@uc.edu
Kleene
Steven J
SJ
D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D003198:Computer Simulation; D054815:Cyclic Nucleotide-Gated Cation Channels; D004553:Electric Conductivity; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008959:Models, Neurological; D018034:Olfactory Receptor Neurons / Q000187:drug effects / Q000502:physiology*; D011894:Rana pipiens
D054815:Cyclic Nucleotide-Gated Cation Channels; D007473:Ion Channels; D000266:Adenylyl Imidodiphosphate; D000584:Amiloride