BC-535 Preliminary, Rev. 060126
16
Optionally, many researchers filter their data using an external device. These devices are
normally of the low-pass 8-pole Bessel design. While Butterworth filters have steeper frequency cutoff
characteristics, they are less commonly used since they tend to overshooting a rapidly varying signal
thus introducing an artifact into the data. In general, it is better to slightly under-filter the data being
acquired in real-time since additional filtering can be performed later in the analysis software.
Warner Instruments provides a number of filtering devices which can be used in conjunction with
the
BC-535
to achieve a high degree of filter resolution. We recommend the use of a high quality
8-pole Bessel filter such as the
LPF-8
.
Acquisition hardware and software
Since the analysis of single channel data is statistical in nature, a large number of channel events
is required to produce significant results. This condition naturally lends itself to the use of a computer.
However, since computers function digitally, the analog signal from the amplifier must first be
digitized by an analog to digital (A/D) converter prior to analysis. Many A/D converters are bundled
with software which emulates a chart recorder or oscilloscope to aid in data acquisition.
Since single channel gating kinetics can range from sub-ms open times to gating transitions
lasting several seconds or more, the desired characteristics of a high-quality A/D converter include
rapid response times, high signal resolution and low noise.
Data analysis
Once the data has been acquired and stored, it must be analyzed for its biophysical
characteristics. Since the volume of data collected is often exceedingly large, analysis is usually
performed by dedicated software programs. The single most popular program for this purpose is
pClamp (Molecular Devices, Sunnyvale, CA). However, several competing software packages are
available commercially or on the Internet. In addition, many investigators have written their own
programs to address their specific needs.
Data archival
The ability to easily archive and retrieve data is an important component of a BLM workstation.
During the course of an average experiment, a large volume of data is collected for later analysis.
Several devices are available for data storage. These devices include, but are not limited to: VCR tape
(requires a signal converter or pulse code modulator), DAT tape, portable or removable hard drives,
Zip or Jazz drives, CD-RW, or the newer DVD-RW technology.
An important advantage of most of these archival systems is that they allow selective access to
previously recorded data for subsequent analysis. The choice of the proper system will depend upon
the needs of the researcher, the financial resources available, and the type of data acquired (fast or
slow channel kinetics resulting in large or small file sizes).
Stirring
Stirring of solutions in the recording chamber is important for the production of reproducible
results, especially following the addition of agonists or antagonists. Additionally, stirring is thought to
facilitate the fusion of vesicles to the bilayer membrane, presumably by vibrating the membrane or by
continuously introducing new vesicles to the bilayer. Ideally, the stirring process should produce
Warner
Instruments
A Harvard Apparatus Company .