Gating mode conversion by proteolysis in a large-conductance K+ channel from embryonic rat telencephalon.

1. In situ patch-clamp recordings of early embryonic large-conductance K+ channels consistently revealed (86% of patches) a complex behaviour characterized by noisy fluctuations between open and closed states of relatively short duration. 2. This behaviour is similar to the buzz mode, a type of gating observed only very rarely in some channels. Its prevalence in proliferative neuroepithelium may thus constitute a criterion of immaturity. 3. In 89% of patches, the buzz mode was converted to a 'normal' mode by intracellular exposure to trypsin. 4. These observations suggest that the immature channel protein includes (or is affected by) a cytoplasmic component, the presence or absence of which determines certain sets of conformational transitions.