Intracellular contribution to extracellularly recorded waveforms: the 'membrane rent' hypothesis

Objective: This investigation uses simulation studies to account for single muscle fiber waveforms with complex configurations as arising from the sim ultaneous recording of a partial intracellular discharge and its associated extracellular manifestation by way of an electrode-induced 'rent' or tear in the sarcolemma. Methods: Published material on intracellular action potentials from healthy and 7 day denervated rat skeletal muscle was used as the basis for calcula tions. A single muscle fiber computer simulation capable of formulating a c ut or crush termination effect used the modeled action potentials to genera te extracellular waveforms at different locations along the muscle fiber. T hese extracellular waveforms were then summated with a varied fraction of t he intracellular action potential to yield a combined potential. These simu lated waveforms were then compared to previously recorded single muscle fib er discharges in order to establish if a combined waveform could reproduce the clinically recorded potentials' configuration. Results: It was not possible to simulate any of the previously detected inn ervated single muscle fiber discharges by combining the action potential's intracellular and extracellular configurations. However, 12 of the 14 clini cally observed complex waveforms documented in denervated tissue could be s imulated with morphologies similar to the clinical potentials. Conclusions: Presumed single muscle fiber discharges with complex configura tions may result from the needle electrode simultaneously recording the act ion potential's intracellular and extracellular waveforms secondary to a 'r ent' in the sarcolemma. This explanation may in part account for some of th e complex appearing potentials detected in denervated tissue, but this 'ren t' hypothesis is likely not the explanation for potentials observed in inne rvated muscle tissue, The apparent success of the 'rent' hypothesis in dene rvated tissue may be a result of the denervated action potential's unique m orphology rather than an actual tear in the sarcolemma. Further investigati ons are necessary to determine if it is possible for a needle electromyogra phic electrode to actually record in part the intracellular action potentia l without disrupting the fiber. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.