Expeirmental Study On Functional Regulation Of Sodium Ionic Channel On Excitable Cell Membrane By Using A Near-infrared Laser

The laser therapy technique has become an effective method in clinic treatment, but the physiological mechanism of most laser medical applications is still unclear. Concerning this issue the researchers focused on the effect of laser irradiation on excitable cell based on the electrophysiological method, the results demonstrated that the laser could modulated the electrophysiological function of excitable cell and evoked action potential directly. And the action potential initiated with the inward flow of sodium ion, this phenomenon indicated that the laser irradiation could affect the function of sodium channel and opened the voltage-gated sodium channel, generated the action potential.Based on the modulation effect of infrared laser on sodium ion channel in excitable cell membrane, electrophysiology mechanism of laser irradiation was studied. The infrared laser at980nm was employed to stimulate the cell membrane, the sodium channel currents without and with laser irradiation were recorded by the patch clamp technique and the change of sodium current was analyzed. Based on the Hodgkin-Huxley(HH) model for description of whole cell current feature, the whole cell currents were fitted and obtained the time constants of sodium current activation and inactivation, τm and τh. The ratio between the time constants without and with laser irradiation was used to represent the influence of laser irradiation on cell viability. In order to measure the photothermal effect caused by laser irradiation, an open pipette method was employed to detect the temperature rise in solution. A glass microelectrode was filled with electrolyte solution and served as thermosensitive element; the pipette resistance was able to response the temperature change at an accuracy of submillisecond in time, and micrometer resolution in space. Based on calibration experiment the actual temperature rise in solution could be obtained.In this paper the temporal modulation and power-dependent modulation of sodium ion channel in neuron cells by near-infrared laser was studied. Through analyzing the experimental results found that:1. The rising edge of laser irradiation at a certain power inhibited the activation of sodium current, accelerated the inactivation of sodium current and the falling edge of laser accelerated both the activation and inactivation of sodium current. Through theoretical analysis on the inhibition effect of the sodium current activation by the rising edge of laser, it was found that the establishment of the photothermal effect by980nm infrared laser irradiation at least needed about lms duration, which was longer than the duration of sodium channel activation. That is to say, in the time span of sodium channel activation the heating effect was not conspicuous and the laser would reduce the activity of the sodium channel as an electromagnetic wave. In the condition of the falling edge of laser the mechanism responsible for the laser modulation on cell function was photothermal effect, the enhancement of the sodium current kinetics could explained by the temperature characteristic of sodium channel protein and the average temperature rise in solution.2. The modulation on cell function by980nm infrared laser with different powers was studied, the kinetics and peak value of sodium current under laser irradiation were analyzed. In the kinetic study laser with different powers was employed to irradiate the sodium channel on cell membrane, the whole cell sodium current was elicited synchronously with the falling edge of laser pulse. The analysis revealed that the averaged ratio of activation constant τm between without and with laser irradiation power was lineally dependent on the laser power, and irrelevant to the cell membrane potential. These results proved that the modulation on sodium current kinetics of neuron cell in vitro by980nm laser with different-irradiation levels was linearly mediated corresponding to the laser-induced photothermal effect. Next the power-dependent of modulation effect on sodium current peak was researched. The changes of sodium currents under laser irradiation with different power were measured and related to the temperature variation of extracellular environment, the experimental result demonstrated that the laser irradiation increased the peak of sodium current. This increment was not only linearly dependent on the laser power but also could be explained by the temperature characteristic of sodium channel protein corresponding to the temperature rises in solution. After laser irradiation, the sodium current amplitude recovery was determined by the rate of solution temperature changes with time, a rapid negative rate of temperature would lead to a better recovery of sodium current from laser irradiation. The deactivation of sodium channel experiments proved that recovery rate was accelerated after laser irradiation. It was indicated that980nm laser irradiation modulated the cell function through both absolutely temperature rise and temperature gradient, the absolutely temperature rise would increase the sodium current peak and the negative temperature gradient would accelerate the recovery of sodium current.In this paper the ion channel mechanism of regulating effect on the cell function by980nm near infrared laser was studied and provided an experimental support to understand the mechanism that action potential inducted by laser irradiation. The sodium channel is the basis for the action potential, responsible for the normal function performing of nerve cells, muscle cells and glands, in other hand the sodium channel ensure the normal metabolism of organisms and served as an important target of drugs, related to the generation and treatment of many disease, therefore this research have considerable reference value for clinical practice of laser medicine.