Gating and Selectivity Properties of a cAMP-Activated K+ Selective Channel from Drosophila Larval Muscle

Abstract

For a while, direct modulation of ion channels by cyclic nucleotides was thought to be confined to those cation-selective ones found in photoreceptors and in vertebrate olfactory neurons (Kaupp, 1991; Zufall, 1994). This idea was fortified by structural and functional similarities exhibited by cyclic nucleotide-gated channels in olfactory neurons with those of photoreceptor cells. The presence of a ciliary axonema in photoreceptors cells pointed out to a unique evolutionary relationship between visual and olfactor y sensory cells. However, cyclic nucleotide activated cation-selective channels have been reported now in a variety of animal cells, including retinal ganglion cells, aorta, testis, kidney, heart and sperm (Yau, 1994). Furthermore, there is increasing evidence for the presence in animals of K+-selective channels that are directly gated by cyclic nucleotides (Delgado et al., 1991; Michael and Asche, 1992; Bruggemann et al., 1993; Gotow, et al., 1994; Gomez and Nassi, 1995; Jorquera et al., 1995; Labarca et al., 1995).