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Previous work from this laboratory has shown that in utero exposure to ethanol significantly alters the synthesis of glycoproteins in synaptic, axolemmal, and myelin membranes from developing rats. In an attempt to determine whether in utero exposure to ethanol similarly alters the synthesis of other glycoconjugates involved with cell-cell interactions, the present study examined the influence of chronic maternal ethanol consumption prior to parturition on the content and synthesis of gangliosides in axolemmal and synaptic plasma membranes from developing rats. The results demonstrate that, in contrast to central nervous system glycoproteins, synaptic and axolemmal glycolipids are minimally affected by in utero exposure to ethanol. At all ages examined (17 to 34 days of age), the offspring of control and ethanol-treated rats had a comparable distribution of radiolabel among synaptic and axolemmal gangliosides, a normal concentration of ganglioside sialic acid in synaptic plasma membranes, and a near-normal distribution of sialic acid among synaptic gangliosides. The present study provides evidence which indicates that the radiolabeling patterns of axolemmal and synaptic membrane gangliosides are similar. Specifically, the most heavily labeled synaptic and axolemmal gangliosides were GT1b (20-37% of the total radioactivity) and GD1a (20-32%). A smaller proportion of radioactivity was associated with GD1b (approximately 11-16%), GM1 (5-10%), and GQ1b (4-11%), as well as with GD3 and the other monosialogangliosides (less than 5%). During the age period examined the proportion of radioactive GT1b increased in both membrane fractions.

Squid giant axons were treated with tetrodotoxin (TTX) in concentrations ranging from 1 nM to 25 nM and the resulting decrease in sodium current was followed in time using the voltage clamp technique. The removal of TTX from the bathing solution produced only partial recovery of the sodium current. This suggests that the over-all interaction is more complex than just a reversible reaction. By correcting for the partial irreversibility of the decrease in sodium current, a dissociation constant of 3.31 x 10(-9)M was calculated for the reaction between TTX and the reactive site of the membrane. The data obtained fit a dose-response curve modified to incorporate the correction for partial irreversibility when calculated for a one-to-one stoichiometry. The fit disagreed with that calculated for a reaction between two molecules of TTX with a single membrane-reactive site, but neither supported nor disproved the possibility of a complex formed by two reactive sites with one molecule of TTX. Values of the rate constants for the formation and dissociation of the TTX-membrane complex, k(1) and k(2), respectively, were obtained from the kinetic data. The values are: k(1) = 0.202 x 10(8)M(-1), and k(2) = 0.116 min(-1). The magnitude of the dissociation constant derived from these values is 5.74 x 10(-9)M, which has the same order of magnitude as that obtained from equilibrium measurements. Arrhenius plots of the rate constants gave values for the thermodynamic quantities of activation.