Evidence of electroconformational changes in membrane proteins: field-induced reductions in intra membrane nonlinear charge movement currents

Off-axis electron holography of bacterial cells and magnetic nanoparticles in liquid

The mapping of electrostatic potentials and magnetic fields in liquids using electron holography has been considered to be unrealistic. Here, we show that hydrated cells of Magnetospirillum magneticum strain AMB-1 and assemblies of magnetic nanoparticles can be studied using off-axis electron holography in a fluid cell specimen holder within the transmission electron microscope. Considering that the holographic object and reference wave both pass through liquid, the recorded electron holograms show sufficient interference fringe contrast to permit reconstruction of the phase shift of the electron wave and mapping of the magnetic induction from bacterial magnetite nanocrystals. We assess the challenges of performing in situ magnetization reversal experiments using a fluid cell specimen holder, discuss approaches for improving spatial resolution and specimen stability, and outline future perspectives for studying scientific phenomena, ranging from interparticle interactions in liquids and electrical double layers at solid-liquid interfaces to biomineralization and the mapping of electrostatic potentials associated with protein aggregation and folding.

Hippocampal neuron loss due to electric injury in rats: a stereological study

Electric injury may cause different changes from minimal damage (e.g. small burns) to severe complications up to death. Several morphological changes of the skin and the internal organs are used for the diagnosis of electrical injury. However, macroscopic findings and histological changes of the internal organs and the skin may be absent in many cases. Furthermore, neuropsychological changes including deficits of cognitive functions may be seen in survivor victims. The aim of the present study is to examine whether electric injury causes decreasing in the number of pyramidal neurons in the rat hippocampus and whether this decreasing can be demonstrated by stereological method. The rats were separated into three groups: first group, native control group; second group, the points of electrical contact were on the back skin in this group; third group, the points of electrical contact were on the temporal region in this group. The current was the usual city current (110V, 50Hz, 100A AC). On the third day, the rats were decapitated; the brains were removed, and sectioned horizontally through the hippocampus and samples chosen according to the systematic random sampling strategy. Afterwards the samples were stained by H&E and optical fractionator method, one of the unbiased stereological methods, was used to estimate the total pyramidal neuron number. The results showed that the total number of pyramidal neurons in three subdivision of the hippocampus (CA3-2 and CA1) was 242,141+/-31,167, 193,388+/-24,795 and 187,448+/-28,300 in the first, second and third groups, respectively. The differences between first and second-third groups were statistically significant (p<0.05). There was not any significant difference between the second and the third groups. In conclusion, electrocution causes loss of the pyramidal neuronal in CA3-2 and CA1 subdivisions of the rat hippocampus in this study.

Gene expression profiles in skeletal muscle after gene electrotransfer

BACKGROUND

Gene transfer by electroporation (DNA electrotransfer) to muscle results in high level long term transgenic expression, showing great promise for treatment of e.g. protein deficiency syndromes. However little is known about the effects of DNA electrotransfer on muscle fibres. We have therefore investigated transcriptional changes through gene expression profile analyses, morphological changes by histological analysis, and physiological changes by force generation measurements. DNA electrotransfer was obtained using a combination of a short high voltage pulse (HV, 1000 V/cm, 100 mus) followed by a long low voltage pulse (LV, 100 V/cm, 400 ms); a pulse combination optimised for efficient and safe gene transfer. Muscles were transfected with green fluorescent protein (GFP) and excised at 4 hours, 48 hours or 3 weeks after treatment.

RESULTS

Differentially expressed genes were investigated by microarray analysis, and descriptive statistics were performed to evaluate the effects of 1) electroporation, 2) DNA injection, and 3) time after treatment. The biological significance of the results was assessed by gene annotation and supervised cluster analysis.Generally, electroporation caused down-regulation of structural proteins e.g. sarcospan and catalytic enzymes. Injection of DNA induced down-regulation of intracellular transport proteins e.g. sentrin. The effects on muscle fibres were transient as the expression profiles 3 weeks after treatment were closely related with the control muscles. Most interestingly, no changes in the expression of proteins involved in inflammatory responses or muscle regeneration was detected, indicating limited muscle damage and regeneration. Histological analysis revealed structural changes with loss of cell integrity and striation pattern in some fibres after DNA+HV+LV treatment, while HV+LV pulses alone showed preservation of cell integrity. No difference in the force generation capacity was observed in the muscles 2 weeks after DNA electrotransfer.

CONCLUSION

The small and transient changes found in the gene expression profiles are of great importance, as this demonstrates that DNA electrotransfer is safe with minor effects on the muscle host cells. These findings are essential for introducing the DNA electrotransfer to muscle for clinical use. Indeed the HV+LV pulse combination used has been optimised to ensure highly efficient and safe DNA electrotransfer.

Synchronization of Na/K pump molecules by a train of squared pulses

We experimentally studied the Na/K pump currents evoked by a train of squared pulses whose pulse-duration is about the time course of Na-extrusion at physiological conditions. The magnitude of the measured pump current can be as much as three-fold of that induced by the traditional single pulse measurement. The increase in the pump current is directly dependent on the number of pre-pulses. The larger the number of the pre-pulses is, the higher the current magnitude can be obtained. At a particular number of pre-pulses, the pump current becomes saturated. These results suggest that a large number of pre-pulses may synchronize the pump molecules to work at the same pace. As a result, the pump molecules may extrude Na ions at the same time corresponding to the stimulation pulses, and pump in K ions at the same time during the pulse intervals. Therefore, the measured pump current is three-fold of that measured by a single pulse where the outward and inward pump currents are canceled each other.

Electroconformational Denaturation of Membrane Proteins

Because of high electrical impedance of cell membrane, when living cells are exposed to an external electric field, the field-induced voltage drops will mainly occur on the cell membrane. In addition to Joule heating damage and electroporation of the cell membrane, the electric field-induced supraphysiological transmembrane potential may inevitably damage the membrane proteins, especially the voltage-dependent membrane proteins. That is because the charged particles in the amino acid of the membrane proteins and, in particular, the voltage-sensors in the voltage-dependent membrane proteins are vulnerable to the membrane potential. An intensive, brief electric shock may induce electroconformational damage or denaturation in the membrane proteins. As a result, the cell functions are significantly reduced. This electric field-induced denaturation in the membrane proteins strongly suggests a new underlying mechanism involved in electrical injury.