Divalent cations and fast axonal transport in chemically desheathed (Triton X-treated) frog sciatic nerve.
We have studied the ability of divalent cations to restore to normal axonal transport (AXT) which was inhibited by deprivation of Ca2+ and/or Mg2+ ions. The epi- and perineurium of the frog sciatic nerve were damaged by a 30-s wash in Triton X-100 containing frog Ringer's. This treatment did not affect either AXT or nerve levels of Ca2+ and Mg2+, but made the ions more easily extractable with a Ca2+- and Mg2+-free Ringer's solution (CMFR). Inhibition of AXT was achieved by incubating Triton X-100-treated nerves in CMFR + EGTA for 5 h, followed by an additional incubation for 12 h in CMFR or Ringer's devoid of only Ca2+ (CFR). These treatments reduced Ca2+ and Mg2+ contents by 77% and 38% respectively. Addition of Ca2+ (1.1 mM) during the 12-h period stimulated AXT, measured as accumulation of 3H-labelled components in front of a ligature, several fold. Mg2+ could not substitute for Ca2+ but potentiated the stimulating effect of Ca2+. Addition of other divalent cations did not affect AXT (Sr2+ and Ba2+) or potentiated the inhibition caused by Ca2+-deprived medium (Mn2+ and Co2+). ATP and creatine phosphate contents were similar in nerves incubated in Ca2+-deprived medium and in Ca2+-containing Ringer's. Thus, inhibition of AXT in the former situation was not due to a decreased availability of high energy phosphates. Two calcium antagonists, D-600 and nifedipin, which are potent smooth muscle relaxants, effectively blocked AXT. The present results suggest that Ca2+ is specifically required to maintain AXT and that an analogy exists between Ca2+ regulation during smooth muscle contraction and AXT.
D000818:Animals; D001370:Axonal Transport / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent; D003902:Detergents / Q000494:pharmacology*; D005711:Gallopamil / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D008854:Microscopy, Electron; D017830:Octoxynol; D011092:Polyethylene Glycols / Q000494:pharmacology*; D011896:Rana temporaria; D012584:Sciatic Nerve / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D013501:Surface-Active Agents / Q000494:pharmacology*
D002413:Cations, Divalent; D003902:Detergents; D013501:Surface-Active Agents; D005711:Gallopamil; D011092:Polyethylene Glycols; D017830:Octoxynol; D008274:Magnesium; D002118:Calcium