AJP - Gastrointestinal and Liver Physiology, Vol 255, Issue 5 696-G699, Copyright © 1988 by American Physiological Society
Methodological errors in radioisotope flux measurements
R. W. Egnor, S. G. Vaccarezza and A. N. Charney
Nephrology Section, Veterans Administration Medical Center, New York, New York.
We examined several sources of error in isotopic flux measurements in a
commonly used experimental model: the study of 22Na and 36Cl fluxes across
rat ileal tissue mounted in the Ussing flux chamber. The experiment
revealed three important sources of error: the absolute counts per minute,
the difference in counts per minute between serial samples, and averaging
of serial samples. By computer manipulation, we then applied hypothetical
changes in the experimental protocol to generalize these findings and
assess the effect and interaction of the absolute counts per minute, the
sampling interval, and the counting time on the magnitude of the error. We
found that the error of a flux measurement will vary inversely with the
counting time and the difference between the consecutive sample counts per
minute used in the flux calculations and will vary directly with the
absolute counts per minute of each sample. Alteration of the "hot" side
specific activity, the surface area of the tissue across which flux is
measured and the sample volume have a smaller impact on measurement error.
Experimental protocols should be designed with these methodological
considerations in mind to minimize the error inherent in measuring isotope
flux.
