Slightly superior performance of bioimpedance spectroscopy over single frequency regression equations for assessment of total body water.

Electrical bioimpedance has been used for several decades to assess body fluid distribution and body composition by using single frequency and bioimpedance spectroscopic (BIS) techniques. It remains uncertain whether BIS methods have better performance compare to single frequency regression equations. In this work the performance of two BIS methods and four different 50 kHz single frequency prediction equations was studied in a data set of wrist-to-ankle tetrapolar BIS measurements (5-1000 kHz) together with reference values of total body water obtained by tritium dilution in 92 patients. Data were compared using regression techniques and Bland-Altman plots. The results of this study showed that all methods produced similarly high correlation and concordance coefficients, indicating good accuracy as a method. Limits of agreement analysis indicated that the population level performance of Sun's prediction equations was very similar to the performance of both BIS methods. However, BIS methods in practice have slightly better predictive performance than the single-frequency equations as judged by higher correlation and the limits of agreement from the Bland-Altman analysis. In any case, the authors believe that an accurate evaluation of performance of the methods cannot be done as long as the evaluation is done using Bland-Altman analysis, the commonly accepted technique for this kind of performance comparisons.

Assessment of potassium current in Royan B(1) stem cell derived cardiomyocytes by patch-clamp technique.

Embryonic stem cells are capable of differentiating to variety of cell tissues including cardiomyocytes. This developmental change is accompanied with a great deal of ion channel expression and functions. Mouse stem cell derived cardiomyocytes were prepared and separated to yield isolated single cell suspension for cell current recording. In the present study some properties of the K(+)-current in Royan B(1) stem cell derived cardiomyocytes were investigated using whole cell patch-clamp technique. When the holding potential was - 60 mV, in some cells a major outward current was elicited by square depolarizing pulses from -60 mV to +50 mV. This outward current was sustained for the duration of 300 ms test pulse. The sustained outward K(+) current was inhibited by tetraethylammonium (10 mM) indicating the activity of Ca(2+) activated K(+) channel in these cells. In some of the cells with 0.2 mM 3,ethylene glycol-bis (ß-aminoethyl ether) N,N,N(`),N(`)-tetraacetic acid in the pipette, only a very small outward current was recorded which suggests that in these cells the voltage activated K(+) channels is either absent or if existed it is not fully functional. Other cells were in far between, indicating that voltage activated K(+) channels are developing in these cells but it is not yet fully functional. In conclusion, we have identified functional large conductance Ca(2+) activated K(+) channel in Royan B(1) stem cell derived cardiomyocytes.