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.
The paper derives fundamental formulae for calculation of large deformations of circular axisymmetric elastic membranes under uniform pressure and then presents and compares several possible solutions. The thorough study gives reader an opportunity to query the matter in detail and therefore to understand the limitations which can occur during calculations of large deformations of membranes. and Práce detailně odvozuje základní vztahy pro výpočet velkých deformací kruhových axisymetrických elastických membrán zatížených rovnoměrným tlakem a následně představuje a srovnává několik možných řešení. Hloubka studie nabízí čtenáři možnost podrobně nahlédnout do problematiky, a tedy dostatečně porozumět úskalím, která při výpočtech velkých deformací membrán mohou nastat a nastávají.