44 • Guide to Electrophysiological Recording
MultiClamp 700A Theory and Operation, Copyright 2000, 2001 Axon Instruments, Inc.
this section, we suggest some approaches to low-noise recording of single channels.
While these same approaches are a good idea for whole-cell recording, they are less
important since in whole-cell recording the dominant noise source comes from the
access resistance in series with the whole-cell capacitance.
Glass Type and Coating
The noise from pipette glass itself arises from the lossy characteristics of its
walls
1
. Therefore, it is expected that glasses with the lowest inherent dielectric
loss will have the lowest noise. Generally, the thicker the wall is, the lower the
noise will be. These expectations have been largely borne out by actual
experiments. Pipette glass can be obtained from specialty glass houses such
as:
Clark Electromedical Instruments
P.O. Box 8, Pangbourne, Reading, RG8 7HU, England, (073) 573-888
Garner Glass
177 S. Indian Hill Road, Claremont, CA 91711, USA, (909) 624-5071
Jencons Scientific
Cherycourt Way Industrial Estate, Stanbridge Road, Leighton Buzzard LU7
8UA, UK, (0525) 372-010
Sutter Instrument Company
51 Digital Drive, Novato, CA 94949, USA, (415) 883-0128
Each type of glass has unique advantages and disadvantages. Aluminosilicate
glasses have lower loss factors, but are hard to pull because of their high softening
temperature. High lead glasses are easier to pull, but have been reported to modify
channel currents (e.g. see Cota and Armstrong, Furman and Tanaka, Biophysical J.
53:107-109, 1988; Furman and Tanaka, Biophysical J. 53:287-292, 1988). Since
1 When a sine voltage is applied across a perfect dielectric, the alternating current should be 90° out of phase with the
voltage. The deviation from 90° is the "loss factor". The loss factor is related to the power dissipated in the dielectric.
Since energy is lost in the dielectric, dielectrics (
e.g.
, glasses) are commonly referred to as "lossy".
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