Ion channel classes in purified olfactory cilia membranes: planar lipid bilayer studies

Abstract

Ciliary membrane fragment fusion to planar lipid bilayers resulted in the insertion of four ion channel types. cAMP-activated, cation-selective channels could be detected only in the absence of Ca2+ and had a conductance of 23 pS. They exhibited an apparent dissociation constant (Kd) for the cyclic nucleotide of approximately 30 microM and an estimated permeability ratio (PNa/PK) of 2.4. The cAMP cation-selective channel coinserted with a K(+)-selective channel refractory to cAMP, Ca2+, and D-myo-inositol 1,4,5-trisphosphate. This K+ channel was voltage independent and exhibited open-conductance substates of 60 and 112 pS. cAMP was also found to modulate a novel K+ channel with a Kd = 140 microM. It displayed three nearly equally spaced open substates with conductances of 34, 80, and 130 pS. In the absence and in the presence of cAMP the probability of occurrence of the open substates was binomially distributed. A fourth channel type was a Ca(2+)-activated K+ channel with a conductance of 240 pS. It was blocked by charybdotoxin at nanomolar concentrations (Kd = 3 nM). These results add support to the idea that, besides cAMP-activated cation-selective channels, vertebrate chemosensory olfactory membranes possess an arrangement of ion channels.

Characterization of Single Channel Currents from Primary Cilia of Renal Epithelial Cells

“…This may have been one of the first demonstrations of TRP vanilloid receptor-type functional channels in cilia. Cyclic AMP activated the 23-pS cation channels in vertebrate olfactory cilia (24) and modulated a high conductance K ϩ channel, displaying several open substates with conductances of 34, 80, and 130 pS (24), which is highly reminiscent of PC2 function (21). The presence of cAMP-activated 8 pS chloride channels has also been determined by steady-state noise analysis of ligand-induced currents (36).…”

“…1d). Primary cilia from confluent LLC-PK1 cells were isolated with a technique adapted from previous reports (24,25). Briefly, confluent LLC-PK1 cells were deciliated by a quick exposure to a high Ca 2ϩ solution and concentrated in a sucrose density gradient.…”

Calcium mediates the activation of the inhibitory current induced by odorants in toad olfactory receptor neurons

“…In addition, this odorant-triggered inhibitory conductance is sensitive to charybdotoxin (CTX), a toxin that blocks Ca 2+ -activated K+ channels [11]. In support of this notion, a CTX-sensitive Ca 2+ -activated K+ conductance has been recently reported to be present in toad olfactory cilia [12].…”

Ca2+‐dependent K+ channels from rat olfactory cilia characterized in planar lipid bilayers

“…Later, a planar lipid bilayer study of a toad olfactory ciliary membrane fraction suggested the presence of a 240 pS conductance BK Ca channel (in symmetrical 200 mM KCl). Its K 0.5 for Ca 2+ was 46 μM and it was blockable by 42 nM ChTx [20]. This channel was presumably derived from the cilia, although the purity of the membrane fraction was not assessed.…”