Eric Trottier

Implication of the C-Terminal Region of the α-Subunit of Voltage-gated Sodium Channels in Fast Inactivation

Abstract. The α-subunit of both the human heart (hH1) and human skeletal muscle (hSkM1) sodium channels were expressed in a mammalian expression system. The channels displayed slow (hH1) and fast (hSkM1) current decay kinetics similar to those seen in native tissues. Hence, the aim of this study was to identify the region on the α-subunit involved in the differences of these current-decay kinetics. A series of hH1/hSkM1 chimeric sodium channels were constructed with the focus on the C-terminal region. Sodium currents of chimeric channels were recorded using the patch-clamp technique in whole-cell configuration. Chimeras where the C-terminal region had been exchanged between hH1 and hSkM1 revealed that this region contains the elements that cause differences in current decay kinetics between these sodium channel isoforms. Other biophysical characteristics (steady-state activation and inactivation and recovery from inactivation) were similar to the phenotype of the parent channel. This indicates that the C-terminus is exclusively implicated in the differences of current decay kinetics. Several other chimeras were constructed to identify a specific region of the C-terminus causing this difference. Our results showed that the first 100-amino-acid stretch of the C-terminal region contains constituents that could cause the differences in current decay between the heart and skeletal muscle sodium channels.This study has uncovered a direct relationship between the C-terminal region and the current-decay of sodium channels. These findings support the premise that a novel regulatory component exists for fast inactivation of voltage-gated sodium channels.

Cysteine scanning analysis of the IFM cluster in the inactivation gate of a human heart sodium channel

UNLABELLED The conserved isoleucine-phenylalanine-methionine (IFM) hydrophobic cluster located in the III-IV linker of voltage-gated sodium channels has been identified as a major component of the fast inactivation gate in these channels. OBJECTIVES The aim of our study was to probe the contribution of each amino acids of the IFM cluster to the inactivation. METHODS A combination of site-directed mutagenesis, cysteine covalent modification and electrophysiological recording techniques were used to elucidate the role of isoleucine1485 and methionine1487 on hH1 sodium channels expressed in tsA201 cells. RESULTS Mutant I1485C behaves like mutant F1486C studied earlier: producing an incomplete inactivation (residual current), a slowing and change in the voltage-dependence of the time constants of current decay, a shift of the steady-state inactivation to more depolarized voltages, and a faster recovery from inactivation than the wild-type hH1. The electrophysiological parameters of mutant M1487C are similar to those of wild-type hH1 except for the presence of a residual current. Exposure of the cytoplasmic surface of the mutants to MTS reagents MTSES, MTSET and MTSBn further disrupted inactivation. In order to explain differences in the amplitude of the sustained currents recorded in the presence of MTSES or MTSET, we studied the effects of exposure of mutants 11485C, F1486C and M1487C to acidic and basic pH in the absence and presence of MTSES and MTSET. The effects of MTSES [negatively charged (-)] and MTSET (+) on the amplitude of the residual current of mutant F1486C were modulated by changes in intracellular pH. CONCLUSION Isoleucine1487 and methionine1485, which surround phenylalanine1487 contribute to stabilizing the inactivation particle for fast inactivation.

Discovery of Peculiar Periodic Spectral Modulations in a Small Fraction of Solar-type Stars

A Fourier transform analysis of 2.5 million spectra in the Sloan Digital Sky Survey was carried out to detect periodic spectral modulations. Signals having the same period were found in only 234 stars overwhelmingly in the F2 to K1 spectral range. The signals cannot be caused by instrumental or data analysis effects because they are present in only a very small fraction of stars within a narrow spectral range and because signal-to-noise ratio considerations predict that the signal should mostly be detected in the brightest objects, while this is not the case. We consider several possibilities, such as rotational transitions in molecules, rapid pulsations, Fourier transform of spectral lines, and signals generated by extraterrestrial intelligence (ETI). They cannot be generated by molecules or rapid pulsations. It is highly unlikely that they come from the Fourier transform of spectral lines because too many strong lines located at nearly periodic frequencies are needed. Finally, we consider the possibility, predicted in a previous published paper, that the signals are caused by light pulses generated by ETI to makes us aware of their existence. We find that the detected signals have exactly the shape of an ETI signal predicted in the previous publication and are therefore in agreement with this hypothesis. The fact that they are only found in a very small fraction of stars within a narrow spectral range centered near the spectral type of the Sun is also in agreement with the ETI hypothesis. However, at this stage, this hypothesis needs to be confirmed with further work. Although unlikely, there is also a possibility that the signals are due to highly peculiar chemical compositions in a small fraction of galactic halo stars.

A technique to detect periodic and non-periodic ultra-rapid flux time variations with standard radio-astronomical data

We demonstrate that extremely rapid and weak periodic and non-periodic signals can easily be detected by using the autocorrelation of intensity as a function of time. We use standard radio-astronomical observations that have artificial periodic and non-periodic signals generated by the electronics of terrestrial origin. The autocorrelation detects weak signals that have small amplitudes because it averages over long integration times. Another advantage is that it allows a direct visualization of the shape of the signals, while it is difficult to see the shape with a Fourier transform. Although Fourier transforms can also detect periodic signals, a novelty of this work is that we demonstrate another major advantage of the autocorrelation, that it can detect non-periodic signals while the Fourier transform cannot. Another major novelty of our work is that we use electric fields taken in a standard format with standard instrumentation at a radio observatory and therefore no specialized instrumentation is needed. Because the electric fields are sampled every 15.625 ns, they therefore allow detection of very rapid time variations. Notwithstanding the long integration times, the autocorrelation detects very rapid intensity variations as a function of time. The autocorrelation could also detect messages from Extraterrestrial Intelligence as non-periodic signals.