ABSTRACT
We describe a new peptide conotoxin affecting sodium current inactivation, that competes on binding with delta-conotoxin TxVIA (delta TxVIA). The amino acid sequence of the new toxin, designated conotoxin NgVIA (NgVIA), is SKCFSOGTFCGIKOGLCCSVRCFSLFCISFE (where O is trans-4-hydroxyproline). The primary structure of NgVIA has an identical cysteine framework and similar hydrophobicity as delta TxVIA but differs in its net charge. NgVIA competes with delta TxVIA on binding to rat brain synaptosomes and molluscan central nervous system and strongly inhibits sodium current inactivation in snail neurons, as does delta TxVIA. In contrast to delta TxVIA, NgVIA is a potent paralytic toxin in vertebrate systems, its binding appears to be voltage-dependent, and it synergically increases veratridine-induced sodium influx to rat brain synaptosomes. delta TxVIA acts as a partial antagonist to NgVIA in rat brain in vivo. NgVIA appears to act via a receptor site distinct from that of delta TxVIA but similar to that of Conus striatus toxin. This new toxin provides a lead for structure-function relationship studies in the delta-conotoxins and will enable analysis of the functional significance of this complex of receptor sites in gating mechanisms of sodium channels.
Subject(s)
Conotoxins , Peptides/metabolism , Receptors, Neurotransmitter/metabolism , Sodium Channel Blockers , Sodium/metabolism , Amino Acid Sequence , Animals , Brain/drug effects , Brain/metabolism , Molecular Sequence Data , Peptides/chemistry , Peptides/isolation & purification , Peptides/toxicity , Protein Binding , RatsABSTRACT
Myo-inositol is an important precursor in cellular second-messenger synthesis. It has been reported to be reduced in the cerebrospinal fluid of depressed patients and to reverse a specific effect of Li on rat behavior when given intracerebroventricularly (i.c.v.). However, myo-inositol enters the brain poorly when given peripherally, and its effects on normal rat brain have not been well studied. A series of experiments examined the effect of intraperitoneal inositol in high doses on locomotor activity, on amphetamine-induced hyperactivity, on apomorphine-induced stereotyped behavior, and on pilocarpine-induced behaviors in rats. In addition, the behavioral effect of i.c.v. inositol was compared to that of a control stereoisomer in untreated and lithium-treated rats. Few effects of peripheral myo-inositol were found in these models. However, peripheral inositol in high doses given to rats exhibiting Li-pilocarpine seizures showed that i.p. inositol could prevent these behaviors, confirming that peripheral inositol may have antidepressant potential in appropriate models.
