Pharmacology is used in combination with most transport techniques as a diagnostic for the involvement of specific transport pathways or the membrane location of a transport process. For instance, mercury (Hg2+) is used as a diagnostic blocker of aquaporins (Niemietz and Tyerman, 2002), tetraethylammonium (TEA+) of K+ channels, gadolinium (Gd3+) of (stretch-activated) cation channels (Demidchik etal., 2002a) and niflumate of anion channels (Roberts, 2006). However, care should be exercised, as some blockers appear to have limited specificity (e.g. niflumate blocks both anion and K+ channels with similar potency, Garrill et al., 1996; and TEA+ has been reported to block aquaporins, Yool et al., 2002). A sensible approach to take when using inhibitors is to screen many compounds to build up a pharmacological profile of a transport process or to use engineered blockers (such as antibodies or synthesised chemical libraries that specifically inhibit particular transport proteins or phenomenon; e.g. Blackwell and Zhao, 2003).
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