Biophysical Properties of a Novel Cationic Channel in the Outer and Inner Membranes of Nuclei from Adult Skeletal Muscle Fibers

Abstract

In spite of some limited progress, the physiological role of cationic ion channels within the nuclear envelope remains largely unknown. Since biophysically distinct channels have been reported within the nuclear envelope of different cells, it is likely that nuclear membrane ion homeostasis is cell-type specific. Here we provide the first identification and characterization of the biophysical properties of the most prominently observed ion channel expressed within the inner and outer membrane of nuclei from adult skeletal muscle fibers. Excised inside-out single channel recordings were obtained from individual nuclei acutely isolated from Flexor Digitorum Brevis (FDB) fibers of wild-type mice. The outer membrane of nuclei was readily accessible following isolation. For measurements of channels from the inner membrane, nuclei were treated with 1 % (w/v) sodium citrate in order to remove the outer membrane. We found that the predominant ion channel expressed in both the inner and outer nuclear membrane was a cationic channel that conducts monovalent ions with slight preference for potassium over sodium ions (a PK/PNa ∼1.22). A 10,000-fold difference in the concentration of free Ca2+ between the pipette and bath solutions did not affect the channel reversal potential in symmetric KCl (∼0 mV), indicating that Ca2+ ions permeation is negligible. The maximum conductance of the channel in the outward direction was ∼162 pS. The mean open probability (PO) was ∼0.7 and voltage-independent between −50 mV to +50 mV. We suggest that this novel monovalent cationic channel within the inner and outer membrane of skeletal muscle nuclei provides a counter-current mechanism that minimizes voltage change across the nuclear membrane. This research was supported by NIH K01 award AR060831(to V.Y.) and NIH R01 grant AR44657 (to R.T.D).