ATOMIC-FORCE MICROSCOPY OF ARTHROPOD GAP-JUNCTIONS

Atomic force microscopy has been used to characterize gap junctions is olated from the hepatopancreas of Nephrops norvegicus, The major polyp eptide of these gap junctions is ductin, a highly conserved 16- to 18- kDa protein. The hydrated gap junctions, imaged in phosphate-buffered saline, appeared as membrane plaques with a thickness of 14 nm, consis tent with their being a pair of apposing membranes, The upper membrane was removed by force dissection using an increased imaging force, The thickness of the lower membrane was 6 nm, giving a separation or gap between the two membranes of 2 nm, High-resolution images show fine de tails of the force-dissected extracellular surfaces, as previously rep orted for vertebrate and heart gap junctions, In addition high-resolut ion AFM images show for the first time detailed substructure on the cy toplasmic face of hydrated gap junctions of either vertebrate or inver tebrate, The plaques had particles on their exposed and force-dissecte d faces. These particles were packed in a hexagonal lattice (a = b = 8 .9 nm on both faces) and had a diameter of similar to 6.5 nm, with a c entral, pore-like depression, Fourier maps calculated from the AFM dat a suggested that each particle was composed of six subunits, These ima ges show a marked similarity to the widely accepted structure of the c onnexon channel of vertebrate gap junctions. (C) 1997 Academic Press.