UMMS Affiliation
Department of Neurology
Publication Date
2020-07-06
Document Type
Article
Disciplines
Cellular and Molecular Physiology | Congenital, Hereditary, and Neonatal Diseases and Abnormalities | Musculoskeletal Diseases | Musculoskeletal System | Nervous System Diseases | Neurology
Abstract
Hyperkalemic periodic paralysis (HyperKPP) manifests as stiffness or subclinical myotonic discharges before or during periods of episodic muscle weakness or paralysis. Ingestion of Ca2+ alleviates HyperKPP symptoms, but the mechanism is unknown because lowering extracellular [Ca2+] ([Ca2+]e) has no effect on force development in normal muscles under normal conditions. Lowering [Ca2+]e, however, is known to increase the inactivation of voltage-gated cation channels, especially when the membrane is depolarized. Two hypotheses were tested: (1) lowering [Ca2+]e depresses force in normal muscles under conditions that depolarize the cell membrane; and (2) HyperKPP muscles have a greater sensitivity to low Ca2+-induced force depression because many fibers are depolarized, even at a normal [K+]e. In wild type muscles, lowering [Ca2+]e from 2.4 to 0.3 mM had little effect on tetanic force and membrane excitability at a normal K+ concentration of 4.7 mM, whereas it significantly enhanced K+-induced depression of force and membrane excitability. In HyperKPP muscles, lowering [Ca2+]e enhanced the K+-induced loss of force and membrane excitability not only at elevated [K+]e but also at 4.7 mM K+. Lowering [Ca2+]e increased the incidence of generating fast and transient contractures and gave rise to a slower increase in unstimulated force, especially in HyperKPP muscles. Lowering [Ca2+]e reduced the efficacy of salbutamol, a beta2 adrenergic receptor agonist and a treatment for HyperKPP, to increase force at elevated [K+]e. Replacing Ca2+ by an equivalent concentration of Mg2+ neither fully nor consistently reverses the effects of lowering [Ca2+]e. These results suggest that the greater Ca2+ sensitivity of HyperKPP muscles primarily relates to (1) a greater effect of Ca2+ in depolarized fibers and (2) an increased proportion of depolarized HyperKPP muscle fibers compared with control muscle fibers, even at normal [K+]e.
Keywords
Cellular Physiology, Contraction and Cell Motility
Rights and Permissions
© 2020 Uwera et al. This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms/). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 International license, as described athttps://creativecommons.org/licenses/by-nc-sa/4.0/)
DOI of Published Version
10.1085/jgp.201912511
Source
Uwera F, Ammar T, McRae C, Hayward LJ, Renaud JM. Lower Ca2+ enhances the K+-induced force depression in normal and HyperKPP mouse muscles. J Gen Physiol. 2020 Jul 6;152(7):e201912511. doi: 10.1085/jgp.201912511. PMID: 32291438. Link to article on publisher's site
Journal/Book/Conference Title
The Journal of general physiology
Related Resources
PubMed ID
32291438
Repository Citation
Uwera F, Ammar T, McRae C, Hayward LJ, Renaud J. (2020). Lower Ca2+ enhances the K+-induced force depression in normal and HyperKPP mouse muscles. Neurology Publications. https://doi.org/10.1085/jgp.201912511. Retrieved from https://escholarship.umassmed.edu/neuro_pp/457
Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.
Included in
Cellular and Molecular Physiology Commons, Congenital, Hereditary, and Neonatal Diseases and Abnormalities Commons, Musculoskeletal Diseases Commons, Musculoskeletal System Commons, Nervous System Diseases Commons, Neurology Commons