INTERNODAL CELLS OF THE GIANT GREEN-ALGA CHARA AS AN EXPRESSION SYSTEM FOR ION CHANNELS

Internodal cells of the giant green alga Chara corallina were utilized as an expression system for two nicotinic acetylcholine receptor subt ypes (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, pa tch-clamp recordings on cytoplasmic droplets were easily performed and single channel activity could be measured with high resolution. The p roperties of the recombinant nAChR observed in this membrane were simi lar to those reported for the channel expressed in Xenopus oocytes, an d 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 chann els. It offers a low-cost and practical alternative to the use of Xeno pus oocytes for the investigation of heterologously expressed ion chan nels.