ELC-03XS User Manual
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version 2.2
page 4
2. Introduction
“Loose patch” recordings (or “loose seal” recordings [Roberts & Almers, 1992]) are used to
record from single excitable cells without damage, i.e. without a direct access to the cell
interior. The first recordings were made around 1960 from muscles cells by Alfred Strickholm
long time before “tight seal” recording was invented by Erwin Neher and Bert Sakmann
twenty years later: “
A method has been developed permitting measurement of membrane
impedance and current, as a function of transmembrane potential, at small, electrically
isolated regions of the muscle cell surface without microelectrode impalement.
”[Strickholm
1961].
The loose seal has a resistance of a few ten to a few hundred M
, and it creates an electrically
isolated access to a single neuron. This isolated area can be used for precise recording,
stimulation or drug and dye application on the single cell level without damaging the cell
[Babour & Isope, 2000]. In contrast to tight seal recordings the same electrode can be reused
for recording from several cells, which is a great advantage.
Since its beginnings several attempts have been made to make such precise extracellular
methods accessible to various preparations. A nice overview can be found in the chapter by
Roberts & Almers [Roberts & Almers, 1992]. Over the years the method was extended to
cultured neurons and brain slice preparations, and also for
in vivo
recordings [Bureau et al,
2004]. The method is particularly well suited for long term recording with little damage to the
recorded neuron [Nunemaker et al, 2003]. It can be used both for somatic and axonal
recording [Khaliq & Raman 2005]. Even subcellular structures such as synaptic boutons are
accessible to loose patch recordings [Auger & Marty, 2000].
Another valuable application of this method is single cell stimulation. The high resistance
loose patch makes possible the application of 1-2 V stimuli to one cell only [Babour & Isope,
2000].
In the nineties of the last century the method of juxtacellular dye application (juxtasomal
filling) became popular [Pinault, 1996]. This staining method is based on repetitive current
pulse trains applied in the close vicinity of cell somata or dendrites and is meanwhile well
established in the field of slice and
in vivo
preparations [Klausberger, 2004]. Juxtacellular
filling together with extracellular measurements are today often summarized under the term
“juxtacellular recording”.
In parallel attempts were made towards transfection of single cells by electroporation using
patch pipettes. DNA or other large molecules were successfully inserted through a patch
pipette into living cells by using an optimized protocol (application of 10 V / 1 ms pulse
trains) [Rathenberg et al, 2003].
Far in excess of classical
in vivo
recording methods [Lalley et al, 1999] several new
approaches are used for monitoring neuronal activity under natural conditions, using new
techniques, e.g. the combination of two photon excitation and patch clamp
in vivo
[Helmchen
et al, 2001; Stosiek et al, 2003; Brecht et al, 2002]. Assays have been developed that allow to
monitor and manipulate single cells under
in vivo
conditions [Brecht et al, 2004]. Besides
sophisticated optics these techniques always require precise recording and stimulation
amplifiers, mostly based on the use of patch electrodes.
