Electrophysiology techniques

This chapter has introduced the membrane ion channels and electro-physiological techniques that may be used for exploring the actions and properties of an important group of anthelmintics. It can be seen that these electrophysiological techniques can be used to explore the mechanisms of anthelmintic resistance. It is hoped that in the future new pharmacological approaches may be produced that can reverse the resistance, perhaps by interfering with the phosphorylation of the ion channels. 

The electrophysiological technique used to measure changes in membrane capacitance is the patch clamp [5,6] in the whole-cell recording mode, where the plasma membrane patch in the pipet is ruptured. In another configuration of the patch clamp, the plasma membrane patch is maintained intact. In this case, small currents due to the opening of individual channels can be measured in the membrane patch. The whole-cell patch clamp... 

After acute PSVT is terminated, long-term preventive treatment is indicated if frequent episodes necessitate therapeutic intervention or if episodes are infrequent but severely symptomatic. Serial testing of antiarrhythmic agents can be evaluated in the ambulatory setting via ambulatory ECG recordings (Holter monitors) or telephonic transmissions of cardiac rhythm (event monitors) or by invasive electrophysiologic techniques in the laboratory. 

There are a number of electrophysiological techniques available which can be used to detect and/or assess neurotoxicity. These techniques can be divided into two broad general categories those focused on central nervous system (CNS) function and those focused on peripheral nervous system function, (Seppalainer, 1975). 

The robustness and large size (diameter 1.2-1.3 mm) of the oocytes make them tolerant to repeated impalement of microelectrode and injection pipettes, permitting functional analysis by a number of electrophysiological techniques. 

HT3 receptor agonists have been shown to enhance the release of endogenous dopamine from striatal slices [14] and to reduce acetylcholine release from sections of rat entorhinal cortex [15]. Furthermore, there are several electrophysiological techniques using a variety of neurones, including those in the gut [25] and primary cultures of brain tissue [26] which respond to 5-HT3 agonist stimulation. 

Table 5.4 Thresholds for odorants in birds, obtained by behavioral, cardiac, and electrophysiological techniques...

Standard superfusion and electrophysiological techniques do not allow to decide whether an H3 heteroreceptor involved in the inhibition of release of a given transmitter is actually located presynaptically (i.e. on the axon terminals) of the respective neurone. Recent (unpublished) data from our laboratory may serve to illustrate this point. In guinea-pig cerebral cortex slices, noradrenaline release is inhibited by histamine via H3 receptors and facilitated via H2 receptors. Using an appropriate technique (see next paragraph) we found that only the H3 but not the H2 receptor is located presynaptically. 

Tests for specific classes of chemicals include the measurement of transmitter stimulated adenyl cyclase and Na/K-ATPase for chemicals that affect receptor function or cholinesterase inhibition for organophosphates or carbamates. Electrophysiological techniques may detect chemicals such as DDT or pyrethroids, which affect impulse transmission. 

Studying Synaptic Vesicle Recycling Using Electrophysiological Techniques-- 28... 

Using superfusion experiments, electrophysiological techniques, pithed animal preparations, and experiments in which transmitter release was determined indirectly via the end-organ response (e.g., twitch response of vas deferens preparations), numerous presynaptic opioid receptors have been identified (Table 2). For the identification of the receptors, classical drug tools were used for future studies, knockout mice (now available for each of the four opioid receptor subtypes) and special nucleotides (e.g., antisense oligodeoxynucleotides or short interfering... 

Many examples of inhibitory presynaptic neuropeptide Y receptors have been found in tissues from experimental animals and humans (Table 3), based on experiments with each of the four techniques described in the Introduction (overflow experiments, electrophysiological techniques, pithed animals, electrically induced twitches in isolated tissues). For the identification of the receptors, the three peptides and modified (e.g., truncated) congeners (Figure 4) were the only tools for many years. More recently, selective antagonists (e.g., in the study by Schwertfeger et al. [2004] on the human heart) and knockout mice (e.g., in the study by Smith-White et al. [2002] on the mouse heart) have been used. According to most studies, only Y2 receptors serve as presynaptic neuropeptide Y receptors. 

During the 1960 s, most of the laboratory effort was exploratory in nature. A variety of techniques were employed to differentiate the spectral channels. In animals, electrophysiological techniques were most rewarding. In humans, the techniques were limited to non-invasionary techniques. These were based primarily on differential (chromatic) adaptation and reflection densitometry. The results for humans will be discussed in Section... 

Recent examples include safety pharmacology s embracement of modem electrophysiological techniques to evaluate the effects of new drugs on the ionic components of the cardiac action potential (Redfem et al. 2003), and telemetry techniques to permit the... 

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