Our kinetic and pharmacological studies indicated in 1997 for the first time that the hormonally regulated K⁺ current involved in TRH-induced modulation of electrical activity and secretory properties of adenohypophysial cells was mediated by a human ether-a-go-go-related (h-ERG) type channel. Subsequent studies combining measurements in native and heterologous expression cell systems have identified several molecular components of the signalling pathway linking phospholipase C-coupled receptors to ERG channel regulation. Furthermore, they pointed to an essential role of the channel cytoplasmic structures on basal h-ERG activation and deactivation properties and hormone-induced alterations of channel gating. However, the structural organization of the long amino and carboxy terminal h-ERG cytoplasmic domains and the molecular basis of their influence on the channel gating machinery remain largely unresolved. Our recent work using a collection of fluorescent h-ERG channels randomly labelled with GFP variants by a transposon-based labelling approach and subsequent fluorescence resonance energy transfer (FRET) measurements, has provided some initial insights about the coarse architercture of the h-ERG cytoplasmic domains. We are presently using a combination of fluorimetric measurements and disulfide bond formation between engineered cysteine pairs for a more direct direct estimation of the amino and carboxy termini relative positioning toward the channel core and for demonstration of physical interactions between the amino end and the cytoplasmic loop linking the h-ERG S4 and S5 transmembrane segments.