Measurement of GABA-evoked conductance changes of lobster muscle fibres by a three-microelectrode voltage clamp technique

Publisher Website
Google Scholar
Abstract
The effective membrane conductance and capacity of lobster muscle fibers was measured by a 3-intracelluar-microelectrode voltage clamp technique. Conductance values agreed well with those determined under current clamp, by means of the short cable equations. Reversible increases in conductance evoked by GABA were reflected by differences (.DELTA.V) in electrotonic potential amplitude recorded at the center, and midway between the center and fiber end, respectively. GABA dose-conductance curves derived from cable theory or from .DELTA.V measurements were virtually identical. The effective capacity (ceff), determined from the area beneath the "on" .DELTA.V capacity transient, yielded values of the membrane time constant consistently lower than those obtained by the graphical method of E. Stefani and A.B. Steinbach, (1969). One possible explanation for this discrepancy is discussed. In the presence of GABA, the effective capacity was reduced in a dose-related manner. The results were interpreted in terms of an equivalent circuit in which surface membrane was arranged in parallel with cleft-tubular membrane of finite conductance, charged through an access resistance. GABA was apparently decreasing ceff by selectively increasing the conductance of the cleft-tubular membranes.