Monovalent Cationic Channel Activity in the Inner Membrane of Nuclei from Skeletal Muscle Fibers

Abstract

Nuclear ion channels remain among the least studied and biophysically characterized channels. Although considerable progress has been made in characterizing calcium release channels in the nuclear membrane, very little is known regarding the properties of nuclear monovalent cationic channels. Here, we describe a method to isolate nuclei from adult skeletal muscle fibers that are suitable for electrophysiological experiments. Using this approach, we show for the first time, to our knowledge, that a nuclear monovalent cationic channel (NMCC) is prominently expressed in the inner membrane of nuclei isolated from flexor digitorum brevis skeletal muscle fibers of adult mice. In isotonic 140 mM KCl, the skeletal muscle NMCC exhibits a unitary conductance of ?160 pS and high, voltage-independent open probability. Based on single-channel reversal potential measurements, NMCCs are slightly more permeable to potassium ions over sodium (PK/PNa = 2.68 ± 0.21) and cesium (PK/PCs = 1.39 ± 0.03) ions. In addition, NMCCs do not permeate divalent cations, are inhibited by calcium ions, and demonstrate weak rectification in asymmetric Ca(2+)-containing solutions. Together, these studies characterize a voltage-independent NMCC in skeletal muscle, the properties of which are ideally suited to serve as a countercurrent mechanism during calcium release from the nuclear envelope.

New Findings: Hindlimb Unloading Causes Nucleocytoplasmic Ca2+ Overload and DNA Damage in Skeletal Muscle

“…Previous studies have reported that myonucleus comprises 50–60% of total nuclei in rat SOL muscle, while myosatellite, vascular endothelial, smooth muscle and nerve cell nuclei account for approximately 2–5%, 10–20% and 20%, respectively [ 23 ]. Morphologically, myonuclei are described as ellipsoidal in shape with a length-to-width ratio of 2.4–4.2 [ 24 ]. In our study, we isolated nuclei from SOL muscle and observed them under a microscope, as shown in Figure 2 A.…”

“…It implies that the Ca 2+ release from nuclear envelope into nucleocytoplasm is enhanced in skeletal muscle cell after hindlimb unloading. IP 3 R channel (subtype 1, IP 3 R1) is also located on the INM and release Ca 2+ from nuclear envelope after binding with IP 3 [ 24 , 39 ]. IP 3 R plays an important role in controlling nuclear Ca 2+ level.…”

Localized nuclear and perinuclear Ca2+ signals in intact mouse skeletal muscle fibers

“…Recently, it has been found that the IP 3 R1 (inositol 1,4,5-triphosphate receptor type 1) is required for the induction of LCSs in skeletal muscle fibers of mice after a hypotonic treatment (Tjondrokoesoemo et al, 2013 ). Single channel recordings of the IP 3 R in isolated nuclei of muscle cells have been described (Kusnier et al, 2006 ) and a large conductance, IP 3 sensitive channel in the inner membrane of nuclei has recently been reported in adult skeletal muscle (Yarotskyy and Dirksen, 2014 ).…”