Techniques electrophysiological identification

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. 

The main experimental use of barium is in electrophysiology where it can be used as a charged probe for metal ion-dependent processes. The isolation and identification of individual ion fluxes which contribute to the electric currents flowing through cell membranes often requires techniques to block specific components of electrical activity. This can sometimes be achieved by the use of the soluble salts of divalent cations such as barium and manganese which may block potassium and calcium and currents in, for example, the cardiac pacemaker [4]. Barium can also be used to identify potassium-conducting channels in isolated membrane vesicles [S,6] or calcium charmels in isolated heart muscle cells, myocytes [7], and adrenal gland chromaffin cells [8]. 

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