CORRECTIONS FOR SPACE-CLAMP ERROR

Daniel K. Hartline and Ann M. Castelfranco

Poster

presented at the Neurons, Networks and Motor Behavior Symposium, University of Arizona, Tucson, AZ November 8-10, 1995 and at the 25th Annual Meeting of the Society for Neuroscience at San Diego, CA, November 12, 1995*.

SUMMARY

In voltage clamp experiments on neurons with attached processes, measurements are subject to error owing to failure of space clamp. As much current research involves voltage clamp under these less-than-iedal conditions, it would be very helpful to be able to assess the seriousness of such errors and, if possible, to correct them reliably. We have been conducting a systematic study of such space-clamp errors and in this poster present corrections for errors in the case of a single uniformly distributed voltage-dependent conductance. Simulated clamp runs were made on model neurons with a passive soma attached to an equivalent-cylinder representation of a dendritic tree possessing Hodgkin-Huxley-type channels with voltage independent time constants. Clamp currents were fitted to the equation:

Errors in the parameters gbar, Vrev, taum, q, tauh, V0 and nu were determined as a function of apparent (i.e. measured) gbar, expressed as a ratio, Gamma', to leak conductance. The figure shows corrections for the four steady-state parameters in the case of an outward current mechanism distributed along a dendrite of electrotonic length L=0.5.

{Note: corrections in the poster (additive or multiplicative) are of the opposite sense from corrections shown in the abstract (subtractive or divisive).}

Panel 1

Notes: Parameters approximate conditions for motorneurons of the spiny lobster stomatogastric ganglion; see Hartline et al. (1993)
; Modeling program NEURON available from Michael Hines.

Panel 2