Internodal cells of the giant green alga Chara corallina were utilized as an expression system for two nicotinic acetylcholine receptor subtypes (nAChR) derived from rat muscle. From Chara internodes that were pressure-injected with the respective cRNA, cytoplasmic droplets were formed, and functional expression of channel proteins in the membrane delineating the droplets was confirmed by patch-clamp techniques. The droplet membrane was recently identified as the original tonoplast, patch-clamp recordings on cytoplasmic droplets were easily performed and single channel activity could be measured with high resolution. The properties of the recombinant nAChR observed in this membrane were similar to those reported for the channel expressed in Xenopus oocytes, and for the native channel recorded in situ. The Chara expression system is, therefore, suitable for functional expression of animal messenger RNAs, without the risk of signal contamination by intrinsic ion channels. It offers a low-cost and practical alternative to the use of Xenopus oocytes for the investigation of heterologously expressed ion channels.
