Nonselective cation channel activated by patch excision from lobster olfactory receptor neurons.
A nonselective cation channel activated by patch excision was characterized in inside-out patches from spiny lobster olfactory receptor neurons. The channel, which was permeable to Na+, K+ and Cs+, had a conductance of 320 pS and was weakly voltage dependent in the presence of micromolar divalent cations. Millimolar internal divalent cations caused a voltage- and concentration-dependent block of Na+ permeation. Analysis of the voltage dependence indicated that the proportion of the membrane's electric field sensed by Mg2+ was greater than 1, suggesting that the channel contains a multi-ion pore. Internal divalent cations also reduced the frequency of channel opening in a concentration-dependent, but not voltage-dependent, manner, indicating that different cation binding sites affect gating and conductance. While block of gating prevented determining if internal divalent cations permeate the channel, a channel highly permeable to external divalent cations was observed upon patch excision to the inside-out configuration. The monovalent and divalent cation conductances shared activation by patch excision, weak voltage dependence, and steady-state activity, suggesting that they are the same channel. These data extend our understanding of this type of channel by demonstrating permeation by monovalent cations, detailing Mg2+ block of Na+ permeation, and demonstrating the channel's presence in arthropods.
Whitney Laboratory, University of Florida, St. Augustine 32086.
T S
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McClintock
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Ache
D000818:Animals; D002412:Cations / Q000378:metabolism*; D002413:Cations, Divalent / Q000494:pharmacology; D002414:Cations, Monovalent / Q000494:pharmacology; D004594:Electrophysiology; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008954:Models, Biological; D008121:Nephropidae; D011984:Sensory Receptor Cells / Q000187:drug effects / Q000378:metabolism*; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D002412:Cations; D002413:Cations, Divalent; D002414:Cations, Monovalent; D007473:Ion Channels; D013757:Tetraethylammonium Compounds