Triethyl tin-induced myelin oedema: an intermediate swelling state detected by X-ray diffraction

X-ray diffraction was used to probe the effects of triethyl tin (TET) on the periodicity and amount of membrane disorientation in the lamellar myelin from respiring optic and sciatic nerves in vitro as well as from nerves of rats treated in vivo through their drinking water. The diffraction patterns show that in vitro TET at concentrations of 4-100 microM affects C.N.S. but not P.N.S. myelin structure. A planar, concentric membrane array with a 200 A period is detected in the C.N.S.; this ordered, swollen myelin contrasts with the vacuolar and vesicular structure seen in thin-sections in TET-induced oedema. No effects of short-term in vivo treatment with TET are observed in either the C.N.S. or P.N.S. The finding that carbonic anhydrase (CA) inhibitors have no effect on the TET-induced structural changes indicates that the swelling we observe is not related to a CA-dependent process. In comparison, the TET effect is prevented by replacing the mobile ions with isotonic sucrose. We conclude that TET-induced swelling in C.N.S. myelin arises from an increase in ion transport followed by obligatory fluid movement. Further, the ordered, swollen structure we detect may be an intermediate state that exists transiently in vivo in TET intoxication and that precedes the gross swelling and vacuolization usually observed.