Ion permeability of ciliary membrane vesicles isolated from Tetrahymena. single-channel recording study on the membrane reconstituted into a planar lipid bilayer

An ion channel in ciliary membrane vesicles isolated from Tetrahymena pyriformis NT-1 was characterized with a single-channel recording technique applied to the membrane reconstituted into a planar lipid bilayer made of soybean phospholipid. The gating of this channel is independent of membrane potential and it spends most of the time in its open-channel state. It is selective for metal cations over gluconate anion although it little distinguishes cations, Ca²⁺, Ba²⁺, Mg²⁺, and K⁺. This channel seems to be identical to the monovalent cation channel in Tetrahymena thermophila BIT cilia, which was recently reported by Oosawa and Sokabe {Am. J. Physiol. 249, C177-C179, 1985). The channel conductance saturates with increasing ion concentration. The maximum value (in pS) for the single-channel conductance obtained in symmetric solutions of sufficiently high concentration is in the order of K⁺(212)>Ba²⁺(41)>Ca²⁺(22)>Mg²⁺(20). On the other hand, the affinity of the channel for these ions is in the reverse order.