Patch clamp recording single channel currents

Figure 4. (a) Planar bilayer membrane system for single-channel currents measurement. Soybean lecithin in n-decane was applied to a hole separating two aqueous chambers. Chambers were filled with metal chloride salt at pH 7.2. The voltage was applied to the outer cell with respect to the inner. The currents across the bilayer were recorded on a PCM recorder through a patch-clamp amplifier and a lowpass filter, (b) Typical records of current observed at -t-50.0 mV (symmetrical 0.5 M solution). Currents increase upward from the zero level shown by the dotted line in each panel. 

In a record obtained by the patch clamp technique, the channel is closed for much of the time (i.e. no current flows across the patch of membrane that contains it), but at irregular intervals the channel opens for a short time, producing a pulse of current. Successive current pulses are always of much the same size in any one experiment, suggesting that the channel is either open or closed, and not half open (there are exceptions to this rule). The durations of the pulses, however, and the intervals between them, vary in an apparently random fashion from one pulse to the next. Hence the openings and closings of channels are stochastic events. This means that, as with many other molecular processes, we can predict when they will occur only in terms of statistical probabilities. But one of the most useful features of the patch clamp method is that it allows observation of these stochastic changes in single ion channels as they actually happen individual protein molecules can be observed in action. 

The patch-clamp data consist in records of single-channel current or on macroscopic current records. The single-channel data is obtained, and properties of current amplitude, duration distributions and probability of single channel events are studied. Macroscopic currents are fitted according to kinetic models, or the noise of current records is analyzed to obtain the microscopoic properties of single-channel events that underlie the macroscopic currents. The analysis methods will not be discussed here. Some criteria and methods are discussed in several articles and reviews, as for example [5, 8, 10, 17-23]. 

Ion channels regulate ion currents and electrochemical potentials across plasma membranes, which are responsible for excitabiUty of nerve, muscle and other type of cells. Single channel current recording using the patch clamp method has revealed electric properties of many kinds of channels at a single... 

The patch-clamp technique is based on the formation of a high resistance seal (109-10lon) between the tip of a glass micropipette and the cell membrane it touches (gigaohm-seal). This technique allows recordings of ionic currents through single ion channels in the intact cell membrane and in isolated membrane patches at a... 

The flow of ions through a single membrane channel (channels are shown in red in the illustration at the left) can he detected hy the patch clamp technique, which records current changes as the channel transits between the open and closed states. [(Left) After E. Neher and B. Sakmann. The patch clamp technique. Copyright 1992 by Scientific American, Inc. All rights reserved. (Right) Courtesy of Dr. Mauricio Montal.]... 

---