The Journal of Neurophysiology Vol. 78 No. 4 October 1997, pp. 2079-2085
Copyright ©1997 The American Physiological Society

Ionic Selectivity of Mechanically Activated Channels in Spider Mechanoreceptor Neurons

Ulli Höger, Päivi H. Torkkeli, Ernst-August Seyfarth, and Andrew S. French

Zoologisches Institut, J. W. Goethe-Universität, D-60054 Frankfurt am Main, Germany; and Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada

Höger, Ulli, Päivi H. Torkkeli, Ernst-August Seyfarth, and Andrew S. French. Ionic selectivity of mechanically activated channels in spider mechanoreceptor neurons. J. Neurophysiol. 78: 2079-2085, 1997. The lyriform slit-sense organ on the patella of the spider, Cupiennius salei, consists of seven or eight 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 ~4.6 nS, 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 (200 to +200 mV) 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 nonsensory cells, most of which are either unselective for monovalent cations or selective for K⁺.

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