On the mechanism of the inhibition of fast axonal transport caused by exposure of frog spinal ganglia to the sodium-deficient medium.
Substitution of choline or sucrose for Na+ in the medium surrounding frog spinal ganglia causes an inhibition of fast axonal transport in vitro. Since an increase Ca2+ influx into neurons does occur in these media, the present experiments examined the possibility that the effect on transport is mediated by an increase in intracellular free Ca2+. The combination of the choline substitution with a 3-fold increase in extracellular Ca2+ reduced transport of [3H] proteins to 75% of control (as compared to the 63% obtained previously with choline alone), thus providing no evidence of an enhancement of choline's effect by a second factor which promotes an increase in intracellular Ca2+. When Li+ was substituted for Na+, the  quantity of [3H] proteins transported fell to 40% of control despite the fact that the Li+ substitution does not modify Ca+ fluxes across the plasma membrane in neurons of the frog spinal nerve. The present findings suggest that removal of Na+ interferes with fast axonal transport by a mechanism other than an increase in intracellular Ca2+
D000818:Animals; D001370:Axonal Transport / Q000187:drug effects*; D002712:Chlorides / Q000494:pharmacology; D002794:Choline / Q000494:pharmacology; D005727:Ganglia, Spinal / Q000187:drug effects / Q000502:physiology*; D008094:Lithium / Q000494:pharmacology; D018021:Lithium Chloride; D009419:Nerve Tissue Proteins / Q000378:metabolism; D011892:Rana catesbeiana; D012964:Sodium / Q000494:pharmacology*
D002712:Chlorides; D009419:Nerve Tissue Proteins; D008094:Lithium; D012964:Sodium; D018021:Lithium Chloride; D002794:Choline