The Ionic Selectivity of Mechanically-Activated Channels in Spider Mechanoreceptor Neurons. ULLI H™GER, PˇIVI H. TORKKELI, ERNST-AUGUST SEYFARTH AND ANDREW S. FRENCH. Zoologisches Institut, J.W. Goethe-Universit„t, D-60054 Frankfurt am Main, Germany, and Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4H7, CanadaZoologisches Institut, J.W. Goethe- Universit„t, D-60054 Frankfurt am Main, Germany, and Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada.
APStracts 4:0100N, 1997.
ABSTRACT
The lyriform slit-sense organ on the patella of the spider, Cupiennius salei, consists of 7-8 slits, with each slit innervated by a pair of mechanically sensitive neurons. Mechanotransduction is believed to occur at the tips of the dendrites, which are surrounded by a Na+ rich receptor lymph. We studied the ionic basis of sensory transduction in these neurons by voltage-clamp measurement of the receptor current, replacement of extracellular cations, and application of specific blocking agents. The relationship between mechanically-activated current and membrane potential could be approximated by the Goldman-Hodgkin-Katz current equation, with an asymptotic inward conductance of about 4.6nS, indicating that 50-230 channels of 20-80 pS each would suffice to produce the receptor current. Amiloride and gadolinium, which are known to block mechanically-activated ion channels, also blocked the receptor current. Ionic replacement showed that the channels are not permeable to choline or Rb+, but are partly permeable to Li+. The receptor current was inward at all membrane potentials (-200mV to +200mV) and never reversed, indicating high selectivity for Na+ over K+. This situation contrasts strongly with insect mechanoreceptors, vertebrate hair cells and mechanically-activated ion channels in non-sensory cells, most of which are either unselective for monovalent cations or selective for K+. 

Received 3 March 1996; accepted in final form 13 June 1997.
APS Manuscript Number J182-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 15 July 1997