A cell constituting an living organism has to exchange ions with the outside via a cell membrane so that the living organism keeps its life. The ion exchange is carried out by a molecule such as a membrane protein, referred to as an ion channel, which exists on the cell membrane. Thus, it is important to study a function of the ion channel on the cell membrane at the time of both basic research and application/development which are carried out in medical science and cell technology.
The ion channel is constituted of a pore which serves as an ion path and a gate which controls closing/opening of a channel. The gate closes/opens upon sensing a membrane potential or a physiologically active substance. This function can be observed by measuring an ion current at the time when the ion permeates the ion channel. As a method for measuring an ion current of a single ion channel, a patch-clamp method is adopted. However, in order to more deeply study correlation of structural functions of the channel, it is necessary to use a simple rearrangement system in carrying out an experiment. In this case, a planar lipid bilayer method is adopted.
In the planar lipid bilayer method, a minimum simple system including ion, water, an artificial lipid bilayer membrane, and an ion channel is used so as to study a basic structure of the ion channel and detail correlation of structural functions thereof (see Non-Patent Document 1). Further, as a device for studying the ion channel in accordance with the planar lipid bilayer method, a measuring device which can simultaneously measure a structure and a function of the ion channel molecule is reported by the inventors of the present invention (see Non-Patent Document 2).
[Non-Patent Document 1]
“New Patch-Clamp Test” written by Shigetoshi Oiki, published by Yoshioka-shoten, 2001, pages 208-215, “19. planar lipid bilayer method for Studying Channel”
[Non-Patent Document 2]
Ide, T., Takeuchi, U., Yanagida, T. Development of an Experimental Apparatus for Simultaneous Observation of Optical and Electrical Signals from Single Ion Channels, Single Mol. 3 (2002)1, pages 33-42
As recited in Non-Patent Document 1 and Non-Patent Document 2, artificial lipid bilayer membranes are formed in the planar lipid bilayer method. Therefore, by forming lipid bilayer membranes which are different from each other in a lipid composition, it is possible to study how the lipid composition influences the ion channel.
However, in the conventional planar lipid bilayer method, once the artificial lipid bilayer membrane is formed, it is impossible to change the lipid composition during the measurement. Thus, in case of studying a relation between the lipid composition and the ion channel, it is necessary to separately form artificial lipid bilayer membranes by separately preparing lipid solutions which are different from each other in the composition.
In this way, according to the conventional planar lipid bilayer method, it is necessary to form another artificial membrane in order to change the lipid composition of the artificial lipid bilayer membrane. This is trouble which is required to be avoided.
Incidentally, a function of the membrane protein serving as the ion channel depends on the lipid composition of the membrane, so that it is highly advantageous to change the lipid composition while measuring the ion permeation in studying the ion channel. However, according to the aforementioned conventional method, it is impossible to observe the relation between the lipid composition and the ion channel with time passage. Moreover, it is sometimes impossible to provide the ion channel in the membrane depending on the lipid composition.