[Show abstract][Hide abstract]ABSTRACT: Voltage-sensor domains (VSDs) in voltage-gated ion channels are thought to regulate the probability that a channel adopts an open conformation by moving vertically in the lipid bilayer. Here we characterized the movement of the VSDs of the prokaryotic voltage-gated sodium channel, NaChBac. Substitution of residue T110, which is located on the extracellular side of the fourth transmembrane helix of the VSD, by cysteine resulted in the formation of a disulfide bond between adjacent subunits in the channel. Our results suggest that T110 residues in VSDs of adjacent subunits can come into close proximity, implying that the VSDs can move laterally in the membrane and constitute a mechanism that regulates channel activity.
Article · Aug 2010 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract]ABSTRACT: Pregnenolone sulfate (PREGS) is an endogenous neurosteroid widely released from neurons in the brain, and is thought to play a memory-enhancing role. At excitatory synapses PREGS facilitates transmitter release, but the underlying mechanism is not known. We addressed this issue at the calyx of Held in rat brainstem slices, where direct whole-cell recordings from giant nerve terminals are feasible. PREGS potentiated nerve-evoked excitatory postsynaptic currents (EPSCs) without affecting the amplitude of miniature EPSCs, suggesting that its site of action is presynaptic. In whole-cell recordings from calyceal nerve terminals, PREGS facilitated Ca2+ currents, by accelerating their activation kinetics and shifting the half-activation voltage toward negative potentials. PREGS had no effect on presynaptic K+ currents, resting conductance or action potential waveforms. In simultaneous pre- and postsynaptic recordings, PREGS did not change the relationship between presynaptic Ca2+ influx and EPSCs, suggesting that exocytotic machinery downstream of Ca2+ influx is not involved in its effect. PREGS facilitated Ba2+ currents recorded from nerve terminals and also from HEK 293 cells expressed with recombinant N- or P/Q-type Ca2+ channels, suggesting that PREGS-induced facilitation of voltage-gated Ca2+ channels (VGCCs) is neither Ca2+ dependent nor VGCC-type specific. The PREGS-induced VGCC facilitation was blocked by the PREGS scavenger (2-hydroxypropyl)-beta-cyclodextrin applied from outside, but not from inside, of nerve terminals. We conclude that PREGS facilitates VGCCs in presynaptic terminals by acting from outside, thereby enhancing transmitter release. We propose that PREGS may directly modulate VGCCs acting on their extracellular domain.
Article · Nov 2006 · European Journal of Neuroscience
[Show abstract][Hide abstract]ABSTRACT: Molecular dependence of vesicular endocytosis was investigated with capacitance measurements at the calyx of Held terminal
in brainstem slices. Intraterminal loading of botulinum toxin E revealed that the rapid capacitance transient implicated as
“kiss-and-run” was unrelated to transmitter release. The release-related capacitance change decayed with an endocytotic time
constant of 10 to 25 seconds, depending on the magnitude of exocytosis. Presynaptic loading of the nonhydrolyzable guanosine
5′-triphosphate (GTP) analog GTPgS or dynamin-1 proline-rich domain peptide abolished endocytosis. These compounds had no
immediate effect on exocytosis, but caused a use-dependent rundown of exocytosis. Thus, the guanosine triphosphatase dynamin-1
is indispensable for vesicle endocytosis at this fast central nervous system (CNS) synapse.