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Journal of Neuroscience, Vol 14, 399-408, Copyright © 1994 by Society for Neuroscience

ARTICLE

Novel hyperpolarization-activated K+ current mediates anomalous rectification in crayfish muscle

A Araque and W Buno
Instituto Cajal, CSIC, Madrid, Spain.

The ionic current underlying anomalous rectification in opener muscle fibers of crayfish was studied under two-electrode voltage clamp. Opener muscle fibers showed a mean resting potential (RP) of -64.8 mV and an input resistance of 0.4 M omega. Hyperpolarizing voltage command pulses from a holding potential (H) of -60 mV evoked an instantaneous voltage-independent linear current (IL) followed by a time- and voltage- dependent inward current (IAB) that reached a steady state within 500 msec. The reversal potential of IAB (EAB) was estimated from tail current amplitudes. At an extracellular K+ concentration ([K+]o) of 5.4 mm the mean EAB was -61.8 mV. EAB shifted toward positive potentials by 50.8 mV for a 10-fold increase in [K+]o. The conductance underlying IAB (GAB) increased sigmoidally with hyperpolarization, starting close to the RP, saturating at a GAB,max of about -140 mV, and showing a mean half-activation at -94.4 mV. The activation curve of GAB shifted 53.6 mV toward positive potentials with a 10-fold increase in [K+]o. GAB,max did not increase in raised [K+]o. The activation and deactivation kinetics of IAB were accurately described by single exponentials with similar time constants (< 100 msec). Time constants changed as an exponential function of the membrane potential. IAB, its time course, GAB, and EAB were not modified in the following conditions: (1) Na(+)- and Ca(2+)-free solutions, (2) intracellular EGTA, (3) extracellular (100 mM) or intracellular tetraethylammonium, (4) extracellular Cs+ (up to 50 mM), Rb+ (up to 10 mM), Ba2+ (13.5 mM), or Mn2+ (13.5 mM). However, low extracellular concentrations of Cd2+ or Zn2+ strongly and reversibly reduced both IL and IAB. Therefore, we conclude that anomalous rectification in crayfish muscle is generated by a voltage- and time-dependent K+ current IAB. This current displayed many electrophysiological and pharmacological characteristics that distinguished it from all others mediating anomalous rectification described previously.

This article has been cited by other articles:

				A. Araque and W. Buno Fast BK-Type Channel Mediates the Ca2+-Activated K+ Current in Crayfish Muscle J Neurophysiol, October 1, 1999; 82(4): 1655 - 1661. [Abstract] [Full Text] [PDF]

				C. Walther, K. E. Zittlau, H. Murck, and K. Voigt Resting Membrane Properties of Locust Muscle and Their Modulation I. Actions of the Neuropeptides YGGFMRFamide and Proctolin J Neurophysiol, August 1, 1998; 80(2): 771 - 784. [Abstract] [Full Text] [PDF]

				A. Araque, A. Marchand, and W. Buno Voltage-Gated and Ca2+-Activated Conductances Mediating and Controlling Graded Electrical Activity in Crayfish Muscle J Neurophysiol, May 1, 1998; 79(5): 2338 - 2344. [Abstract] [Full Text] [PDF]

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