Ion permeation through hyperpolarization-activated membrane channels (Q-channels) in the lobster stretch receptor neurone.
In the lobster stretch receptor neurone it is possible to demonstrate a hyperpolarization-activated membrane current, IQ, which appears to be carried by Na+ and K+ in combination. The ion permeability of the membrane channel conducting this current (Q-channel) was investigated using conventional electrophysiological techniques including intracellular ion concentration measurements. It was found that none of the ions choline, protonated Tris, Rb+, NH4+, Li+, and protonated hydroxylamine was able to pass through the Q-channel which, thus, appears to be permeable to Na+ and K+ only. With increasing extracellular Na+ concentrations, IQ was increased up to a saturation level. This behaviour could be described by a one-site-two-barriers version of the Eyring rate theory, assuming that the permeant ions are turned over at specific saturable channel sites which 'sense' 70% of the transmembrane potential difference. With increasing extracellular K+ concentrations, IQ was increased in accordance with a simple first-order dose-response relationship. This finding can be accounted for by assuming that K+ increases all rates of turn-over of the permeant ions at their specific sites by similar relative amounts. Changes in extracellular Na+ and K+ concentrations were found to have no effect on the gating properties of the Q-channel.
Edman
A
A
Department of Physiology and Biophysics, University of Lund, Sweden.
Grampp
W
W
D000818:Animals; D004553:Electric Conductivity; D019811:Hydroxylamine; D006898:Hydroxylamines / Q000378:metabolism; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D008094:Lithium / Q000378:metabolism; D008433:Mathematics; D008465:Mechanoreceptors / Q000378:metabolism*; D008564:Membrane Potentials; D008954:Models, Biological; D008121:Nephropidae; D009474:Neurons / Q000378:metabolism; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology
D006898:Hydroxylamines; D007473:Ion Channels; D000644:Quaternary Ammonium Compounds; D019811:Hydroxylamine; D008094:Lithium; D012964:Sodium; D012413:Rubidium; D011188:Potassium