When measuring cell membrane electrical capacitance in whole cell configuration using alternating currents, the resolution decreases with increasing membrane conductance and pipette resistance. Improved resolution was attained by the dual-frequency method which was modified as to control the voltage amplitude of one of the measuring frequencies. A model circuit was developed for the verification of the method. This circuit allows measurement of calibrated capacitance changes even in the range of 5 to 20 fF. Moreover, the method was applied to capacitance measurements on pancreatic exocrine acinar cells. The results of measurements on the model as well as on pancreatic acinar cells are presented. The principle can also be applied to other hardware and software methods for measuring electrical cell membrane parameters.
A system for the evaluation of temperature changes in living tissue at a dimensional level of a single cell is described. A glass micropipette the tip of which is filled with semiconducting glass (Rech et al. 1992), is used as a microsensor. The changes of conductivity of the sensor due to variations of temperature are evaluated by electronic circuitry based on the measurement of an AC current of sinusoidal waveform flowing through the sensor. Temperature changes in the range of 0.01 K can be detected in this way.
We proposed a temperature sensitive microelectrode for rapid measurements of temperature at the cellular level. In principle, the electrical impedance of the tip of the microelectrode changes with temperature. We designed an impulse measurement system (STEP) sensitive to the above changes of impedance. The system is based on a presettable negative input impedance of the current to a voltage converter. We compared the efficiency of the new STEP with the currently used RAMP system. We found following advantages of the STEP system: i) the danger of high voltage oscillations which could mechanically destroy the microelectrode tip is eliminated; ii) this system provides the opportunity to set the maximum sensitivity of the system according to the measured temperature interval. Moreover, the STEP method makes it possible to measure the resistance by using a sinusoidal stimulation signal which has to be preliminarily compensated by a rectangular signal. The shortest sampling period of the new system represents 0.1 ms with a resolution higher than 0.1 K and sensitivity better than 30 mV/K.
The electrical parameters of the cell membrane are mostly estimated employing ac methods. The measurement is based on the analysis of the current(s) flowing through an access resistance and the membrane. A current/potential transducer is used at the input of the device. The parameters of this transducer, especially its feedback capacity, degrades the accuracy of the measurement and hence diminishes the suppression of mutual influences of the individual parameters. The paper suggests a possible software correction and is supplemented by remarks for practical application., V. Rohlíček, F. Rech., and Obsahuje bibliografii