Patch-clamp technique, identification

Researchers at the MoneU Center (Philadelphia, Pennsylvania) are using a variety of electrophysical and biochemical techniques to characterize the ionic currents produced in taste and olfactory receptor cells by chemical stimuli. These studies are concerned with the identification and pharmacology of the active ion channels and mode of production. One of the techniques employed by the MoneU researchers is that of "patch clamp." This method aUows for the study of the electrical properties of smaU patches of the ceU membrane. The program at MoneU has determined that odors stimulate intraceUular enzymes to produce cycUc adenosine 3, 5 -monophosphate (cAMP). This production of cAMP promotes opening of the ion channel, aUowing cations to enter and excite the ceU. MoneU s future studies wiU focus on the connection of cAMP, and the production of the electrical response to the brain. The patch clamp technique also may be a method to study the specificity of receptor ceUs to different odors, as weU as the adaptation to prolonged stimulation (3). 

These approaches to receptor identification and classification were, of course, pioneered by studies with peripheral systems and isolated tissues. They are more difficult to apply to the CNS, especially in in vivo experiments, where responses depend on a complex set of interacting systems and the actual drug concentration at the receptors of interest is rarely known. However, the development of in vitro preparations (acute brain slices, organotypic brain slice cultures, tissue-cultured neurons and acutely dissociated neuronal and glial cell preparations) has allowed more quantitative pharmacological techniques to be applied to the action of drugs at neurotransmitter receptors while the development of new recording methods such as patch-clamp... 

We have reviewed the major calcium permeant ion channels in smooth muscle, summarized in Figure 8. The obvious complexity and redundancy of these channels almost certainly reflects evolutionary pressures associated with the diversity of functions subserved by smooth muscle. Progress in this area has generally proceeded by the identification and biophysical characterization of these channels using patch-clamp or bilayer techniques, followed by the determination of their molecular structure and regulatory properties. With the notable exception of metabotropic, nonse-... 

Where a definitive identification of the contents of the munition is required, it will normally be necessary to breach the munition case and take and analyse a sample of the chemical fill. This is a difficult and hazardous task, and will normally be attempted only in the field, in exceptional circumstances. Techniques for safely penetrating a munition in the field have, however, been developed. One system, developed by the United Kingdom, is based on the use of a commercial nail gun to penetrate the case of thin walled munitions. A special rubber patch is first placed on the wall of the munition and the nail gun, fitted with a specially designed hardened steel pin, is clamped to the wall of the munition. The gun is set up so that it can be fired remotely, and when this is done the steel pin is driven through the rubber patch and penetrates the wall of the munition. The rubber patch reduces the risk of leakage due to any over-pressure present within the munition. Once the pin has been safely inserted, the munition is transferred to a sealed glovebox. The pin can then be carefully removed and a sample of the fill extracted via the resulting hole in the munition wall for chemical analysis. 

---