Regarding the discussion about the (lack of) emphasis on metabolism in drug
discovery.....
There is one method fairly widely in use in the pharmaceutical industry
(and, to some extent, in academia) that relies on monitoring energy
metabolism in living cells. It's called microphysiometry, and it employs a
semiconductor-based pH sensor in a flow chamber (volume ~3 uL, flow rate ~1
uL/s, ~100,000 cells) to detect the rate at which the cells acidify their
environment. The pH excursions are no more than 0.1 unit, and cells
(eukaryotic or prokaryotic; adherent or nonadherent) can be kept happy for
many hours. Time resolution, based on fluid mixing and the time to make an
acidification-rate measurement, is about 1 minute.
This measurement of the rate of production of acidic products of energy
metabolism (CO2, lactic acid) is one empirical index of the rate of energy
metabolism. While it has obvious limitations in terms of mechanistic
interpretations, it has proven a relatively general way of detecting
physiological changes in cells when they are exposed to some test compound.
It's especially useful for detecting receptor activation, fairly
independently of the mechanism of signal transduction. In many cases,
receptor activation leads to 10% to 100% changes in acidification rate,
usually transient but sometimes sustained.
Anyone interested in more information can check the following references:
*Parce et al. (1989) "Detecting of cell-affecting agents with a silicon
biosensor," Science 242:243.
*McConnell et al. (1992) "The Cytosensor microphysiometer: Biological
applications of silicon technology," Science 257:1906.
*Owicki et al. (1994) "The light-addressable potentiometric sensor:
Principles and biological applications," Ann. Rev. Biophys. Biomol.
Struct. 23:87.
Disclaimer: I do R&D at the company that sells the microphysiometer
instrument.
------------------------------------------------------------
John C. Owicki, Ph.D.
Associate Technical Director & FLIPR Applications Manager
Molecular Devices Corporation
1311 Orleans Drive
Sunnyvale, CA 94089
E-mail: jack_owicki at moldev.com
Phone: (408) 747-3514; Fax: (408) 747-3601
