John E. Remmers (1), Stanley A. Schultz (1), Jacqueline Wallace (1),
Ryuji Takeda (2) and Akira Haji (2,*)
(1) Respiratory Research Group, University of Calgary, Calgary, Alberta
T2N 4N1, Canada
(2) Department of Pharmacology, Faculty of Medicine, Toyama Medical and
Pharmaceutical University, 2630 Sugitani, Toyama 930-01, Japan
(*) To whom correspondence should be addressed.
Abstract: Investigation of the identity and modes of action of
neurotransmitters in the mammalian central nervous system can be facilitated
by simultaneous intracellular recording of membrane potential and extracellular
iontophoresis of agonists and antagonists. We describe here techniques for
conveniently constructing a compound microelectrode, originally described
by Sonnhof (Pflugers Arch 341, 351 - 358, 1973), suitable for such studies.
The Sonnhof electrode consists of two components, a centraxial micropipette
for recording membrane potential surrounded by a cylindrical array of 6
pipettes for iontophoresis. The cylindrical array tapers coaxially and terminates
in 6 contiguous, crescent-shaped orifices surrounding the terminal portion
of the central pipette, 25 - 50 microm from the tip. Pipettes were constructed
from borosilicate glass tubing of 1-mm wall thickness having a 10-mm or
16-mm outer diameter. The resistances, flux and transport numbers for iontophoresis
of glycine were measured for pipettes constructed from both sizes of glass.
Flux increased with increasing levels of current, and transport number decreased
with increasing micropipette resistance. A spherical diffusion model points
out the steep dependence of steady state concentration on diffusional distance,
stressing the importance of diminishing the distance between the iontophoresis
source and the recording site. This is particularly true when brief pulses
of current are used.
Keywords: Transport number, Brief pulse application, Diffusional distance,
Membrane potential, Iontophoresis