DOI: 10.5061/dryad.sqv9s4n49
title: The role of action potential changes in depolarization-induced failure of excitation contraction coupling in mouse skeletal muscle

description: Excitation-contraction coupling (ECC) is the process by which electrical
 excitation of muscle is converted into force generation. Depolarization of
 skeletal muscle resting potential contributes to failure of ECC in
 diseases such as periodic paralysis, intensive care unit acquired weakness
 and possibly fatigue of muscle during vigorous exercise. When
 extracellular K+ is raised to depolarize the resting potential, failure of
 ECC occurs suddenly, over a narrow range of resting potentials.
 Intracellular recordings of action potentials (APs) in individual mouse
 skeletal muscle fibers during depolarization of the resting potential
 revealed small APs are still generated at resting potentials at which
 force production has failed. Simultaneous imaging of Ca2+ transients and
 recording of APs demonstrated failure to generate Ca2+ transients when APs
 peaked at potentials more negative than -30 mV. An AP property that
 closely correlated with failure of the Ca2+ transient was the integral of
 AP voltage with respect to time. Simultaneous recording of Ca2+ transients
 and APs with electrodes separated by 1.6 mm revealed AP conduction fails
 when APs peak below -21 mV. We hypothesize propagation of APs and
 generation of Ca2+ transients are governed by distinct AP properties: AP
 conduction is governed by AP peak, whereas Ca2+ release from the
 sarcoplasmic reticulum is governed by AP integral of voltage with respect
 to time. The reason distinct AP properties may govern separate steps of
 ECC is the kinetics of the ion channels involved in the different steps of
 ECC. Na channels, which govern propagation, have rapid kinetics such that
 propagation is insensitive to AP width (and integral) whereas Ca2+ release
 is governed by movement of gating charges in Cav1.1 channels, which have
 slower kinetics such that Ca2+ release is sensitive to AP width (and
 integral). The quantitative relationships established between resting
 potential, AP properties, AP conduction and Ca2+ transients provide the
 foundation for future studies of failure of ECC induced by depolarization
 of the resting potential.
description: Two electrode
 intracelllular recordings from mouse EDL fibers and muscle force
 recordings from mouse EDL muscles. Simultaneous with the intracellular
 recording, Ca transients were imaged.  Raw traces have been analyzed and
 data entered into excel spreadsheets.
description: Data set #1:  Force data for Fig 1A. It consists of 1 sheet.
 Column A lists the time during the experiment. Columns B through M
 represent 1 muscle each and show the normalized force generated at each
 time point. The title states the extracellular K concentration that was
 infused. Column N lists when the various extracellular K concentration was
 changed. Data set
 #2: Intracellular recording of APs and ΔF/F for Fig 1. The excel file
 consists of 5 sheets. The extracellular K concentration the muscle was
 incubated in is the title of each sheet. Each sheet has 5 columns with
 data in them. The first column in each sheet is the date of the
 experiment. The second column lists the muscle fiber number from each
 muscle. Each muscle was used for several different K concentrations such
 that it appears on more than 1 data sheet. For this reason, the fiber
 number sometimes starts at a large number as the muscle was already used
 for a lower K concentration. The third column is the resting potential at
 the time the action potential was recorded. The fourth column of data is
 the action potential peak, and the fifth column of data is the normalized
 ΔF/F triggered by the action potential. The ΔF/F in the data sheet is
 normalized to 100%. Data sets #3, 4 and 5: These data
 sets were used to generate the plots in Fig 2 E, F and G respectively.
 Each excel file has data from the same 12 fibers and if desired could be
 combined into 1 excel spread sheet with all the values for each fiber. In
 each file, data from each fiber is represented as 2 columns. The first is
 the x axis for each plot and the second column is the y axis for each
 plot. The rows represent measurements taken every 5s during infusion of
 solution containing 16 mM K. Data set #6: This data set has
 the data used to perform the analysis shown in Fig 3. There are 6 rows of
 data for each fiber. The first row is the resting potentials, the second
 is the AP peak, the third is the normalized AP peak, the fourth is the
 normalized delta F/F, the fifth is the AP area and the sixth is the
 normalized AP area. The columns in red starting at column BU were
 normalizations that were not correct. The values were used to calculate
 the correct normalization. Data set #7 is the data used to
 generate the plots for the two example fibers shown in Fig 4 where the
 electrodes are 1.6 mm apart. There are two data sheets. Each sheet
 represents the analysis for 1 of the fibers. Column A is the date the
 recording was performed. Column B is the fiber number. Column C is the
 sweep number; each sweep is separated by 5s in time. Column D is the
 action potential peak for each sweep recorded 1.6 mm from the stimulating
 electrode. Column E is the resting potential. Columns F through Y are the
 un-normalized image intensities of the 20 ROIs analyzed for the signal
 generated following stimulation for each sweep. Column F is the ROI by the
 stimulating electrode and column Y is by the recording
 electrode. Data
 set #8 is the data used to generate the plots for the two example fibers
 shown in Fig 5 where the stimulating and recording electrodes are close
 together. There are two data sheets. Each sheet represents the analysis
 for 1 of the fibers. Column A is the date the recording was performed.
 Column B is the fiber number. Column C is the sweep number; each sweep is
 separated by 5s in time. Column D is the action potential peak for each
 sweep. Column E is the resting potential. Columns F through Y are the
 un-normalized image intensities of the 20 ROIs analyzed for the signal
 generated following stimulation for each sweep. The stimulating and
 recording electrodes are both near the ROI at column O. Data set #9 is the data used to
 generate the plots for the fiber shown in Fig 6 where the stimulating and
 recording electrodes are close together. There is one data sheet. Column A
 is the date the recording was performed. Column B is the fiber number.
 Column C is the sweep number; each sweep is separated by 5s in time.
 Column D is the action potential peak for each sweep. Column E is the
 resting potential. Columns F through Y are the un-normalized image
 intensities of the 20 ROIs analyzed for the signal generated following
 stimulation for each sweep. The stimulating and recording electrodes are
 both near the ROI at column O. At row 57 the stimulus duration was
 increased from 0.2 ms to 5 ms such that “action potential” peak was
 increased from -35 to +56 mV.