THE BIOELECTRICAL SOURCE IN COMPUTING SINGLE MUSCLE-FIBER ACTION-POTENTIALS

Generally, single muscle fiber action potentials (SFAPs) are modeled a s a convolution of the bioelectrical source (being the transmembrane c urrent) with a weighting or transfer function, representing the electr ical volume conduction. In practice, the intracellular action potentia l (IAP) rather than the transmembrane current is often used as the sou rce, because the IAP is relatively easy to obtain under experimental c onditions. Using a core conductor assumption, the transmembrane curren t equals the second derivative of the IAP. In previous articles, discr epancies were found between experimental and simulated SFAPs. Adaptati ons in the volume conductor slightly altered the simulation results. A nother origin of discrepancy might be an erroneous description of the source. Therefore, in the present article. different sources were stud ied. First, an analytical description of the IAP was used. Furthermore , an experimental IAP, a special experimental SFAP, and a measured tra nsmembrane current scaled to our experimental situation were applied. The results for the experimental IAP were comparable to those with the analytical IAP. The best agreement between experimental and simulated data was found for a measured transmembrane current as source, but di fferences are still apparent.