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Ca 2+ ‐ or Mg 2+ ‐Stimulated ATPase Activity in Bullfrog Spinal Nerve: Relation to Ca 2+ Requirements for Fast Axonal Transport
Author(s) -
Hammerschlag Richard,
Bobinski Judith A.
Publication year - 1981
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1981.tb01707.x
Subject(s) - bullfrog , chemistry , atpase , biophysics , radiochemistry , enzyme , endocrinology , biochemistry , biology
Adenosine triphosphatase (ATPase) activity stimulated by Ca 2+ or Mg 2+ was characterized in spinal nerve and spinal sensory ganglion of bullfrog. Enzyme activity of homogenates from both sources reached a maximum at a 1‐2 mM concentration of either cation, although the level of maximal activity in nerve trunks was approximately twice that in ganglia. Enzyme activation was not observed with 2 mM‐Sr 2+ or Ba 2+ , Co 2+ or Mn 2+ , at 2 mM, depressed Ca 2+ activation of the enzyme by 50‐60% in nerve but had no inhibitory effect on ganglia activity. In intact spinal gangliodspinal nerve preparations, incubated for 20 h in medium containing 0.2 mM‐Co 2+ , no effect was detected on Ca 2+ /Mg 2+ ATPase activity in ganglia or nerve trunks whereas fast axonal transport was inhibited by 80%. Incubation in medium containing 0.02 mM‐Hg 2+ depressed enzyme activity in ganglia by 64% and in nerve trunks by 44%, whereas fast transport was again inhibited by 80%. When only nerve trunks were exposed to these ions, Hg 2+ but not Co 2+ was observed to slow the rate of fast axonal transport. The divalent cation specificity of the Ca 2+ /Mg 2+ ATPase activity is distinct from the ion specificities, determined in previous work, of the Ca 2+ requirement during initiation of fast axonal transport in the soma, and of the Ca 2+ requirement during translocation in the axon. Thus, previous observations of Ca 2+ ‐dependent events in fast axonal transport cannot be taken per se to suggest the involvement of Ca 2+ /Mg 2+ ATPase in the transport process.