Dataset Information

Alternating bipolar field stimulation identifies muscle fibers with defective excitability but maintained local Ca(2+) signals and contraction.

ABSTRACT: Most cultured enzymatically dissociated adult myofibers exhibit spatially uniform (UNI) contractile responses and Ca(2+) transients over the entire myofiber in response to electric field stimuli of either polarity applied via bipolar electrodes. However, some myofibers only exhibit contraction and Ca(2+) transients at alternating (ALT) ends in response to alternating polarity field stimulation. Here, we present for the first time the methodology for identification of ALT myofibers in primary cultures and isolated muscles, as well as a study of their electrophysiological properties.We used high-speed confocal microscopic Ca(2+) imaging, electric field stimulation, microelectrode recordings, immunostaining, and confocal microscopy to characterize the properties of action potential-induced Ca(2+) transients, contractility, resting membrane potential, and staining of T-tubule voltage-gated Na(+) channel distribution applied to cultured adult myofibers. Here, we show for the first time, with high temporal and spatial resolution, that normal control myofibers with UNI responses can be converted to ALT response myofibers by TTX addition or by removal of Na(+) from the bathing medium, with reappearance of the UNI response on return of Na(+). Our results suggest disrupted excitability as the cause of ALT behavior and indicate that the ALT response is due to local depolarization-induced Ca(2+) release, whereas the UNI response is triggered by action potential propagation over the entire myofiber. Consistent with this interpretation, local depolarizing monopolar stimuli give uniform (propagated) responses in UNI myofibers, but only local responses at the electrode in ALT myofibers. The ALT responses in electrically inexcitable myofibers are consistent with expectations of current spread between bipolar stimulating electrodes, entering (hyperpolarizing) one end of a myofiber and leaving (depolarizing) the other end of the myofiber. ALT responses were also detected in some myofibers within intact isolated whole muscles from wild-type and MDX mice, demonstrating that ALT responses can be present before enzymatic dissociation.We suggest that checking for ALT myofiber responsiveness by looking at the end of a myofiber during alternating polarity stimuli provides a test for compromised excitability of myofibers, and could be used to identify inexcitable, damaged or diseased myofibers by ALT behavior in healthy and diseased muscle.

SUBMITTER: Hernandez-Ochoa EO

PROVIDER: S-EPMC4743112 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Alternating bipolar field stimulation identifies muscle fibers with defective excitability but maintained local Ca(2+) signals and contraction.

Hernández-Ochoa Erick O EO Vanegas Camilo C Iyer Shama R SR Lovering Richard M RM Schneider Martin F MF

Skeletal muscle 20160205

<h4>Background</h4>Most cultured enzymatically dissociated adult myofibers exhibit spatially uniform (UNI) contractile responses and Ca(2+) transients over the entire myofiber in response to electric field stimuli of either polarity applied via bipolar electrodes. However, some myofibers only exhibit contraction and Ca(2+) transients at alternating (ALT) ends in response to alternating polarity field stimulation. Here, we present for the first time the methodology for identification of ALT myofi ...[more]

PMID: 26855765

Similar Datasets

Project description:Nuclear Ca(2+) is important for the regulation of several nuclear processes such as gene expression. Localized Ca(2+) signals (LCSs) in skeletal muscle fibers of mice have been mainly studied as Ca(2+) release events from the sarcoplasmic reticulum. Their location with regard to cell nuclei has not been investigated. Our study is based on the hypothesis that LCSs associated with nuclei are present in skeletal muscle fibers of adult mice. Therefore, we carried out experiments addressing this question and we found novel Ca(2+) signals associated with nuclei of skeletal muscle fibers (with possibly attached satellite cells). We measured localized nuclear and perinuclear Ca(2+) signals (NLCSs and PLCSs) alongside cytosolic localized Ca(2+) signals (CLCSs) during a hypertonic treatment. We also observed NLCSs under isotonic conditions. The NLCSs and PLCSs are Ca(2+) signals in the range of micrometer [FWHM (full width at half maximum): 2.75 ± 0.27 μm (NLCSs) and 2.55 ± 0.17 μm (PLCSs), S.E.M.]. Additionally, global nuclear Ca(2+) signals (NGCSs) were observed. To investigate which type of Ca(2+) channels contribute to the Ca(2+) signals associated with nuclei in skeletal muscle fibers, we performed measurements with the RyR blocker dantrolene, the DHPR blocker nifedipine or the IP3R blocker Xestospongin C. We observed Ca(2+) signals associated with nuclei in the presence of each blocker. Nifedipine and dantrolene had an inhibitory effect on the fraction of fibers with PLCSs. The situation for the fraction of fibers with NLCSs is more complex indicating that RyR is less important for the generation of NLCSs compared to the generation of PLCSs. The fraction of fibers with NLCSs and PLCSs is not reduced in the presence of Xestospongin C. The localized perinuclear and intranuclear Ca(2+) signals may be a powerful tool for the cell to regulate adaptive processes as gene expression. The intranuclear Ca(2+) signals may be particularly interesting in this respect.

Project description:Bipolar Disorder (BD) is a complex neuropsychiatric disorder that is characterized by intermittent episodes of mania and depression and, without treatment, 15% of patients commit suicide1. Hence, among all diseases, BD has been ranked by the WHO as a top disorder of morbidity and lost productivity2. Previous neuropathological studies have revealed a series of alterations in the brains of BD patients or animal models3, such as reduced glial cell number in the patient prefrontal cortex4, up-regulated activities of the PKA/PKC pathways5-7, and changes in dopamine/5-HT/glutamate neurotransmission systems8-11. However, the roles and causation of these changes in BD are too complex to exactly determine the pathology of the disease; none of the current BD animal models can recapitulate both the manic and depressive phenotypes or spontaneous cycling of BD simultaneously12,13. Furthermore, while some patients show remarkable improvement with lithium treatment, for yet unknown reasons, other patients are refractory to lithium treatment. Therefore, developing an accurate and powerful biological model has been a challenge for research into BD. The development of induced pluripotent stem cell (iPSC) technology has provided such a new approach. Here, we developed a human BD iPSC model and investigated the cellular phenotypes of hippocampal dentate gyrus neurons derived from the patient iPSCs. Using patch clamp recording, somatic Ca2+ imaging and RNA-seq techniques, we found that the neurons derived from BD patients exhibited hyperactive action potential (AP) firing, up-regulated expression of PKA/PKC/AP and mitochondria-related genes. Moreover, lithium selectively reversed these alterations in the neurons of patients who responded to lithium treatment. Therefore, hyper-excitability is one endophenotype of BD that is probably achieved through enhancement in the PKA/PKC and Na+ channel signaling systems, and our BD iPSC model can be used to develop new therapies and drugs aimed at clinical treatment of this disease. total RNAseq from neurons generated from BD patient-specific iPS cells

Dataset Information

Alternating bipolar field stimulation identifies muscle fibers with defective excitability but maintained local Ca(2+) signals and contraction.

Publications

Alternating bipolar field stimulation identifies muscle fibers with defective excitability but maintained local Ca(2+) signals and contraction.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets