Estimated single-channel conductance of mechanically-activated channels in a spider mechanoreceptor

Noise analysis was used to estimate the single-channel conductance and number of channels responsible for the mechanically-activated current in the sensory neurons of a spider mechanoreceptor organ. External slits of the VS- 3 slit-sense organ in the patellar cuticle of Cupiennius salei were moved with a piezoelectric stimulator while glass microelectrodes penetrated the adjacent cell bodies. Receptor currents were measured by the switching single-electrode voltage clamp technique during both step and ramp displacements of the slits. Current records were segmented in time, and the variance and amplitude of the current were obtained from each segment, to allow fitting of the variance vs. amplitude relationship by a standard equation based on a two-state channel. Mean values of 7.5 pS and 253 were obtained for the conductance and number of channels from 75 separate recordings. These values are in good agreement with the small number of other estimates of these parameters from different mechanoreceptor preparations.