Inhibition of potassium-stimulated acetylcholine release from rat brain cortical slices by two high-affinity analogs of vesamicol

The vesicular acetylcholine transporter is required for neuromuscular development and function

The vesicular acetylcholine (ACh) transporter (VAChT) mediates ACh storage by synaptic vesicles. However, the VAChT-independent release of ACh is believed to be important during development. Here we generated VAChT knockout mice and tested the physiological relevance of the VAChT-independent release of ACh. Homozygous VAChT knockout mice died shortly after birth, indicating that VAChT-mediated storage of ACh is essential for life. Indeed, synaptosomes obtained from brains of homozygous knockouts were incapable of releasing ACh in response to depolarization. Surprisingly, electrophysiological recordings at the skeletal-neuromuscular junction show that VAChT knockout mice present spontaneous miniature end-plate potentials with reduced amplitude and frequency, which are likely the result of a passive transport of ACh into synaptic vesicles. Interestingly, VAChT knockouts exhibit substantial increases in amounts of choline acetyltransferase, high-affinity choline transporter, and ACh. However, the development of the neuromuscular junction in these mice is severely affected. Mutant VAChT mice show increases in motoneuron and nerve terminal numbers. End plates are large, nerves exhibit abnormal sprouting, and muscle is necrotic. The abnormalities are similar to those of mice that cannot synthesize ACh due to a lack of choline acetyltransferase. Our results indicate that VAChT is essential to the normal development of motor neurons and the release of ACh.

Regulation of acetylcholine synthesis and storage

Acetylcholine is one of the major modulators of brain functions and it is the main neurotransmitter at the peripheral nervous system. Modulation of acetylcholine release is crucial for nervous system function. Moreover, dysfunction of cholinergic transmission has been linked to a number of pathological conditions. In this manuscript, we review the cellular mechanisms involved with regulation of acetylcholine synthesis and storage. We focus on how phosphorylation of key cholinergic proteins can participate in the physiological regulation of cholinergic nerve-endings.

Halothane enhances exocytosis of [3H]-acetylcholine without increasing calcium influx in rat brain cortical slices

1. The effect of halothane on the release of [3H]-acetylcholine ([3H]-ACh) in rat brain cortical slices was investigated. 2. Halothane (0.018 mM) did not significantly affect the basal and the electrical field stimulation induced release of [3H]-ACh. However, halothane (0.063 mM) significantly increased the basal release of [3H]-ACh and this effect was additive with the electrical field stimulation induced release of [3H]-ACh. 3. The release of [3H]-ACh induced by 0.063 mM halothane was independent of the extracellular sodium and calcium ion concentration and was decreased by tetracaine, an inhibitor of Ca(2+)-release from intracellular stores or dantrolene, an inhibitor of Ca(2+)-release from ryanodine-sensitive stores 4. Using 2-(4-phenylpiperidino)-cyclohexanol (vesamicol), a drug that blocks the storage of ACh in synaptic vesicles, we investigated whether exocytosis of this neurotransmitter is involved in the effect of halothane. Vesamicol significantly decreased the release of [3H]-ACh evoked by halothane. 5. It is suggested that halothane may cause a Ca2+ release from intracellular stores that increases [3H]-ACh exocytosis in rat brain cortical slices.