Time-resolved IR spectroscopy reveals mechanistic details of ion transport in the sodium pump Krokinobacter eikastus rhodopsin 2.

We report a comparative study on the structural dynamics of the light-driven sodium pump Krokinobacter eikastus rhodopsin 2 wild type under sodium and proton pumping conditions by means of time-resolved IR spectroscopy. The kinetics of KR2 under sodium pumping conditions exhibits a sequential character, whereas the kinetics of KR2 under proton pumping conditions involves several equilibrium states. The sodium translocation itself is characterized by major conformational changes of the protein backbone, such as distortions of the α-helices and probably of the ECL1 domain, indicated by distinct marker bands in the amide I region. Carbonyl stretch modes of specific amino acid residues helped to elucidate structural changes in the retinal Schiff base moiety, including the protonation and deprotonation of D116, which is crucial for a deeper understanding of the mechanistic features in the photocycle of KR2.

Initiation and blocking of the action potential in an axon in weak ultrasonic or microwave fields.

In this paper, we analyze the effect of the redistribution of the transmembrane ion channels in an axon caused by longitudinal acoustic vibrations of the membrane. These oscillations can be excited by an external source of ultrasound and weak microwave radiation interacting with the charges sitting on the surface of the lipid membrane. It is shown, using the Hodgkin-Huxley model of the axon, that the density redistribution of transmembrane sodium channels may reduce the threshold of the action potential, up to its spontaneous initiation. At the significant redistribution of sodium channels in the membrane, the rarefaction zones of the transmembrane channel density are formed, blocking the propagation of the action potential. Blocking the action potential propagation along the axon is shown to cause anesthesia in the example case of a squid axon. Various approaches to experimental observation of the effects considered in this paper are discussed.

980-nm infrared laser modulation of sodium channel kinetics in a neuron cell linearly mediated by photothermal effect.

Photothermal effect (PE) plays a major role in the near-infrared laser interaction with biological tissue. But, quite few interactions can be quantitatively depicted. Here, a two-step model is proposed to describe a 980-nm infrared laser interaction with neuron cell in vitro. First, the laser-induced temperature rises in the cell surrounding area were measured by using an open pipette method and also calculated by solving the heat conduction equation. Second, we recorded the modifications on sodium (Na) channel current in neuron cells directly by using a patch clamp to synchronize the 980-nm laser irradiation and obtained how the electrophysiological function of neuron cells respond to the temperature rise. Then, the activation time constants, τ(m), were extracted by fitting the sodium currents with the Hodgkin-Huxley model. The infrared laser modulation effect on sodium currents kinetics was examined by taking a ratio between the time constants with and without the laser irradiations. The analysis revealed that the averaged ratio at a specific laser exposure could be well related to the temperature properties of the Na channel protein. These results proved that the modulation of sodium current kinetics of a neuron cell in vitro by 980-nm laser with different-irradiation levels was linearly mediated corresponding to the laser-induced PE.

Modulation of sodium currents in rat sensory neurons by nucleotides.

The effects of various nucleotides on the fast tetrodotoxin-sensitive (f-TTX-S) and the slow tetrodotoxin-resistant (s-TTX-R) sodium currents in rat dorsal root ganglion (DRG) neurons were investigated using the patch-clamp technique. Nucleoside triphosphates (NTPs; ATP, GTP, UTP and CTP) and nucleoside diphosphates (NDPs; ADP, GDP, UDP and CDP) decreased f-TTX-S current, whereas they increased s-TTX-R current, when currents were evoked by step depolarizations to 0 mV from a holding potential of -80 mV. NTPs and NDPs shifted both the conductance-voltage relationship curve and the steady-state inactivation curve in the hyperpolarizing direction in both types of sodium currents. Most of them also increased the maximum conductance of s-TTX-R current. ITP, a derivative of ribonucleotide, and dTTP, a deoxyribonucleotide, modulated both types of sodium currents similarly to NTPs and NDPs. However, nucleoside monophosphates (NMPs; AMP, GMP, UMP and CMP) and adenosine had little or no effect on either type of sodium current. Therefore, it seems that nucleotides, regardless of the kind of base, should have two or more phosphates to be able to modulate sodium currents in DRG neurons. Extracellular nucleotides with di- or tri-phosphates would influence the perception by modulating sodium currents in sensory neurons. Particularly, the increase of the maximum conductance and the hyperpolarizing shift of the conductance-voltage relationship of s-TTX-R sodium current would result in an intensified nociception.

[Effects of microwave irradiation on ATPase activity and voltage dependent ion channel of rat hippocampus cell membrane].

OBJECTIVE: To study the effect of microwave irradiation on hippocampus cell. METHOD: Changes of ATPase activity and voltage dependent ion channel of hippocampus cell membrane were observed in mice exposed to 2 450 MHz microwave irradiation of 10 mW/cm2 from a physical therapy machine. Histochemical method and patch clamp method were used to determine the activity of Na+, K(+)-ATPase, Ca2+, Mg(2+)-ATPase and voltage dependent Na+, K+, Ca2+ channels respectively. RESULT: 1) Na+, K(+)-ATPase activity of microwave irradiated mice showed no significant change as compared with the control, but the activity of Ca2+, Mg(2+)-ATPase decreased significantly (P< 0.05); 2) In microwave irradiated mice, Na+, K+, Ca2+, current inducement rate in hippocampus neuron decreased significantly, the membrane voltage of Na+ current peak shifted to depolarization, and the attenuation rate of Na+ current and current A inducement rate decreased significantly as compared with control mice. CONCLUSION: Irradiation of 2 450 MHz microwave at a doze of 10 mW/cm2 was not fatal to mice hippocampus cell. But Ca2+, Mg(2+)-ATPase activity of hippocampal cell membrane and voltage dependent Na+, K+, Ca2+ ion channel of hippocampal nervous were affected which would affect study and memory.

Molecular basis for function in sodium channels.

Na+ channels earned their unique role in excitable cells because of two functional properties, finely honed by evolution. The first is their exquisite sensitivity to small changes of membrane potential: a depolarization of only 10 mV can increase open probability by as much as two orders of magnitude. The second is the rapidity with which they respond to changes of membrane potential: their gates begin to open tens of microseconds after a depolarization. These features are built into two sets of moving parts: voltage sensors that respond directly to changes of membrane potential, and gates that open and close in response to voltage sensor movement. We have explored these movements using a combination of electrophysiology, site-directed mutagenesis, cysteine accessibility scanning and photoactivated cross-linking using a bifunctional cysteine reagent. The main voltage sensors of Na+ channels are four homologous S4 segments, each of which has a unique functional role. These transmembrane segments are almost completely surrounded by hydrophilic crevices. The membrane electric field moves these positively charged helices through a short, hydrophobic 'gating pore'. The minimum contact between an S4 segment and its gating pore insure that a small movement can rapidly move several of its charged residues across the electric field.

Effects of extremely-low-frequency electromagnetic fields on ion transport in several mammalian cells.

We have investigated the effects of sinusoidal electromagnetic fields (EMF) on ion transport (Ca2+, Na+, K+, and H+) in several cell types (red blood cells, thymocytes, Ehrlich ascites tumor cells, and HL60 and U937 human leukemia cells). The effects on the uptake of radioactive tracers as well as on the cytosolic Ca2+ concentration ([Ca2+]i), the intracellular pH (pHi), and the transmembrane potentsial (TMP) were studied. Exposure to EMF at 50 Hz and 100-2000 microT (rms) had no significant effects on any of these parameters. Exposure to EMF of 20-1200 microT (rms) at the estimated cyclotron magnetic resonance frequencies for the respective ions had no significant effects except for a 12-32% increase of the uptake of 42K within a window at 14.5-15.5 Hz and 100-200 microT (rms), which was found in U937 and Ehrlich cells but not in the other cell types.

[Postradiation changes of active ion transport systems of the CNS. The effect of superlethal doses of ionizing radiation on the Na,K pump in surviving brain slices]. / Postradiatsionnye izmeneniia v sistemakh aktivnogo transporta ionov v TsNS. Vliianie sverkletal'nykh doz ioniziruiushchei radiatsii na Na,K-nasos v perezhivaiushchikh srezakh mozga.

Active potassium ion transport in surviving sections of rat brain was irreversibly inhibited 6 min, 1 h and 6 h following whole-body single X irradiation. At the same time, the accumulation of products of lipid peroxidation and phospholipase hydrolysis was followed up during the development of radiation pathology. The relationship was noted between the postirradiation changes in the physicochemical status of lipids of the membrane and the impairment of its transport function.

[The action of ionizing radiation on neuronal function in the edible snail. Phospholipase A2 and the Na+ and K+ transport systems]. / Deistvie ioniziruiushchei radiatsii na funktsional'noe sostoianie neironov vinogradnoi ulitki. Fosfolipaza A2 i sistemy transporta Na+ i K+.

A study was made of the influence of A2 phospholipase on 22Na release from cells of nerve ganglia of edible snail. The treatment of nerve ganglia with A2 phospholipase inhibits Na, K-pump of neuronal membranes and does not exert a substantial effects on Na/Ca metabolism. There is a similarity between the effects of ionizing radiation and A2 phospholipase on the release of 22Na from cells.