Effects of Ionic Strength of Immersion Medium on the Structure of Peripheral Nerve Myelin

Abstract

As part of a general study of the effects of various ions on the low-angle x-ray diffraction patterns of nerve myelin, specimens were immersed in aqueous media containing ions in the proportions recommended for Ringer's solution but at hypertonic and hypotonic strengths. Observations were made which may have great significance in relation to the role of ions and of water in myelin structure. Materials and MethodsOnly data on the frog sciatic nerve are reported in this paper. Segments of nerve trunk were immersed in ionic media for various lengths of time and then mounted in thin walled glass capillary tubes for examination by x-ray diffraction using high resolution low-angle cameras (1) and Cu K,* radiation. After preliminary experiments, studies were concentrated on specimens which had been immersed in normal (N), hypertonic (10 N), and hypotonlc (N/4) Ringer's solutions, 0.25, 0.9, and 10 per cent saline, and Ringer's solution in which the Ca ++ concentration alone had been increased to 10 1,;. After examination by x-ray diffraction, the specimens were either dried and reexamined later, or immersed in normal Ringer's solution and reexamined after a further 16 to 24 hours. RESULTSThe most interesting low-angle diffraction patterns were those obtained after 20 to 24 hours in 10 ~ and ~/4 Ringer's solutions. Photometer traces of such patterns, together with a trace obtained from nerve immersed in normal strength Ringer's solution, are shown in Fig. 1. The 270 A band from the N/4 specimen can be seen to be clearly resolved in the original diffraction patterns but the photometer fails to resolve it to more than a marked shoulder in the trace.The detailed changes of diffraction pattern resulting from immersion of the nerve specimens in hypertonic and hypotonic solutions will be described separately. Hypertonie Solutions:In the early stage of modification of myelin structure by 10 N Ringer's solution there is an apparent strengthening of the third order x-ray reflection 89

Quantitative study of the non‐circularity of myelinated peripheral nerve fibres in the cat

“…Markedly hypotonic solutions, as expected, produce an abrupt marked increase in myelin period of as much as 8 nm (Finean & Millington, 1957) due to 'a reopening throughout the myelin spiral of the primitive inesaxon gap' (Robertson, 1958), that is, due to separation at the intraperiod line. Markedly hypertonic solutions also produce an increase of about 2 nm in the myelin period in the frog (Finean & Millington, 1957). Probably lyophilic molecules and ions in the hypertonic solutions penetrate the myelin and increase its volume by taking in with them their own bound water (Robertson, 1958).…”

“…The myelin period in peripheral nerve does, of course, depend to some extent upon the degree of hydration of the sheath, myelin having a water content of 40-50 %. Markedly hypotonic solutions, as expected, produce an abrupt marked increase in myelin period of as much as 8 nm (Finean & Millington, 1957) due to 'a reopening throughout the myelin spiral of the primitive inesaxon gap' (Robertson, 1958), that is, due to separation at the intraperiod line. Markedly hypertonic solutions also produce an increase of about 2 nm in the myelin period in the frog (Finean & Millington, 1957).…”

Membrane Interactions Are Altered in Myelin Isolated from Central and Peripheral Nervous System Tissues

“…Structural alterations induced by hypotonic treatments are reversed in both intact CNS (Lalitha and Worthington, 1975;Inouye and Kirschner, 1988a) and PNS (Finean and Millington, 1957;Worthington and Blaurock, 1969) myelins as indicated by the reappearance of the native x-ray pattern when saline is reintroduced. Similarly, native or native-like patterns from isolated CNS and PNS myelins were re-stored in the presence of saline at neutral pH.…”

Myelin

“…Water-miscible organic solvents such as methanol, ethanol, or acetone produced dehydration, whereas treatment with longer-chain alcohols, chloroform, and chloroform-methanol produced an irreversible disruption of the ordered structure (Elkes and Finean, 1953a;Fernandez-Maran and Finean, 1957;Rumsby and Finean, 196fu,b). Finean and Millington ( 1957) showed that the packing arrangement of the membrane 1/as.sA 1/3.9A .. .. Mokrasch et al (1971), N eurosci. R es.…”

“…Finean and Burge (1963) and Moody (1963) mapped the Fourier transform of the diffracting unit of myelin by measuring the diffraction patterns from swollen myelin lattices. Finean and Millington (1957) had shown by X-ray diffraction that swelling of peripheral nerve myelin in hypotonic solutions increased the repeat period from 170 A to values in the range 250-270 A. Robertson (1958) observed in electron micrographs of swollen myelin that the myelin membranes separate at their external surfaces while remaining closely apposed at their cytoplasmic surfaces.…”