Calcium ion stimulated protein kinases in myelin

Arachidonic acid and its metabolites increase Cai in cultured rat oligodendrocytes

Fluorescence measurements of intracellular calcium (Cai) were made on cultured rat spinal cord oligodendrocytes (OLGs) using the dye fura-2. Exposure of OLGs to arachidonic acid (AA) (5-50 microM) elicited a concentration-dependent increase in Cai that was derived mainly from extracellular Ca2+. AA at 50 microM also released Ca2+ from intracellular stores. The response to AA was not decreased by nifedipine or by inhibition of Na(+)-Ca2+ exchange. AA-induced Ca2+ influx pathway was permeable to Mn2+ and Co2+ but not to Ba2+ and was not markedly influenced by depolarization, suggesting that AA activates a voltage-independent, not strictly selective, Ca2+ channel. The Cai response to AA was partially attenuated in the presence of indomethacin, indicating that the Cai response was mediated in part by cyclooxygenase products of AA. However, the AA-induced Cai response far exceeded that induced by prostaglandins and was mimicked by linoleic acid. We conclude that AA modulates Cai of OLGs via two mechanisms: 1) indirectly via cyclooxygenase pathway and 2) directly via membrane lipid-protein interaction.

The role of calcium in rat oligodendrocyte injury and repair

The role of intracellular calcium in oligodendrocyte injury is investigated using cultured rat oligodendrocytes. Calcium ionophores A23187 and ionomycin mimic both complement and perforin attack, causing oligodendrocyte lysis at concentrations which do not lyse other glia. Membrane vesiculation, the mechanism by which oligodendrocytes resist and recover from complement and perforin attack, is also induced by A23187. Oligodendrocytes are more susceptible to complement attack in the presence of a calmodulin inhibitor (W7), which also inhibits vesiculation. These results imply that calmodulin is involved in membrane repair from complement attack, and indicate that changes in intracellular calcium play an important yet paradoxical role in the oligodendrocyte response to injury, dictating both susceptibility and cellular recovery.

Immunochemical evidence of phosphorylation of a new 23K basic protein in rat brain myelin

Myelin from developing rat brain (8-44 day-old rat) was incubated in vitro with [gamma-32P]ATP to determine how many basic proteins were phosphorylated. Myelin proteins were separated by polyacrylamide gel electrophoresis and transferred to nitrocellulose sheets. The nitrocellulose sheets were stained with antisera to human basic protein by the immunoblot technique. Five basic proteins with molecular weights of 23K, 21.5K, 18.5K, 17K, and 14K were distinctly immunostained. These basic proteins were found to be phosphorylated when the same nitrocellulose sheets were exposed to x-ray film. The in vitro phosphorylation of 23K and 21.5K basic proteins appear to decrease with maturation of the brain. The result of this study suggests that intense phosphorylation of various forms of basic proteins, in particular 23K and 21.5K basic proteins, during the initial stages of myelin formation, may play a pivotal role in the compaction of myelin membrane.

Phospholipid-sensitive Ca2+ -dependent protein kinase preferentially phosphorylates serine-115 of bovine myelin basic protein

Phospholipid-sensitive Ca2+ -dependent protein kinase (PL-Ca-PK) and cyclic AMP-dependent protein kinase (A-PK) both preferentially phosphorylated serine residues of bovine myelin basic protein (MBP). Tryptic peptide maps of MBP phosphorylated by PL-Ca-PK or A-PK, however, revealed different phosphopeptides, suggesting a difference in the intramolecular substrate specificity for the two enzymes. Serine-115 of MBP, in the sequence (-Arg-Phe-Ser(115)-Trp-), was found to be a preferred and probably major phosphorylation site for PL-Ca-PK. Because serine-115 of bovine MBP corresponds to serine-113 of rabbit MBP, an in vivo phosphorylation site reported by Martenson et al. (1983), and PL-Ca-PK is present at a very high level in brain and myelin, it is suggested that the enzyme may be responsible for the in vivo phosphorylation of this and other sites in MBP.