LOCALIZATION OF INDIVIDUAL CALCIUM CHANNELS AT THE RELEASE FACE OF A PRESYNAPTIC NERVE-TERMINAL

Studies using biophysical techniques suggest a highly structured organ ization of calcium channels at the presynaptic transmitter release fac e (Llinas et al., 1981; Stanley, 1993), but it has not as yet proved p ossible to localize identified channels at tho required nanometer leve l of resolution. We have used atomic force microscopy on the calyx-typ e nerve terminal of the chick ciliary ganglion to localize single calc ium channels tagged via biotinylated omega-conotoxin GVIA to avidin-co ated 30 nm gold particles. Calcium channels were in low (modal value a pproximately less than or equal to 1 per mu(2)) and high (modal value approximate to 55 per mu m(2)) density areas and exhibited a prominent interchannel spacing of 40 nm, indicating an intermolecular linkage. Particles were observed in clusters and short linear or parallel linea r arrays, groupings that may reflect calcium channel organization at t he transmitter release site.