title: Sarcoplasmic reticulum K(+) (TRIC) channel does not carry essential countercurrent during Ca(2+) release.
abstract: The charge translocation associated with sarcoplasmic reticulum (SR) Ca(2+) efflux is compensated for by a simultaneous SR K(+) influx. This influx is essential because, with no countercurrent, the SR membrane potential (Vm) would quickly (<1 ms) reach the Ca(2+) equilibrium potential and SR Ca(2+) release would cease. The SR K(+) trimeric intracellular cation (TRIC) channel has been proposed to carry the essential countercurrent. However, the ryanodine receptor (RyR) itself also carries a substantial K(+) countercurrent during release. To better define the physiological role of the SR K(+) channel, we compared SR Ca(2+) transport in saponin-permeabilized cardiomyocytes before and after limiting SR K(+) channel function. Specifically, we reduced SR K(+) channel conduction 35 and 88% by replacing cytosolic K(+) for Na(+) or Cs(+) (respectively), changes that have little effect on RyR function. Calcium sparks, SR Ca(2+) reloading, and caffeine-evoked Ca(2+) release amplitude (and rate) were unaffected by these ionic changes. Our results show that countercurrent carried by SR K(+) (TRIC) channels is not required to support SR Ca(2+) release (or uptake). Because K(+) enters the SR through RyRs during release, the SR K(+) (TRIC) channel most likely is needed to restore trans-SR K(+) balance after RyRs close, assuring SR Vm stays near 0 mV.
authors.affiliation: Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, Illinois, USA.
authors.forename: Tao
authors.initials: T
authors.lastname: Guo
authors.forename: Alma
authors.initials: A
authors.lastname: Nani
authors.forename: Stephen
authors.initials: S
authors.lastname: Shonts
authors.forename: Matthew
authors.initials: M
authors.lastname: Perryman
authors.forename: Haiyan
authors.initials: H
authors.lastname: Chen
authors.forename: Thomas
authors.initials: T
authors.lastname: Shannon
authors.forename: Dirk
authors.initials: D
authors.lastname: Gillespie
authors.forename: Michael
authors.initials: M
authors.lastname: Fill
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D007473:Ion Channels / Q000378:metabolism*; D032342:Muscle Cells / Q000166:cytology; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*
chemical_list: D007473:Ion Channels; D002110:Caffeine; D002118:Calcium