title: TRIC-B channels display labile gating: evidence from the TRIC-A knockout mouse model.
abstract: Sarcoplasmic/endoplasmic reticulum (SR) and nuclear membranes contain two related cation channels named TRIC-A and TRIC-B. In many tissues, both subtypes are co-expressed, making it impossible to distinguish the distinct single-channel properties of each subtype. We therefore incorporated skeletal muscle SR vesicles derived from Tric-a-knockout mice into bilayers in order to characterise the biophysical properties of native TRIC-B without possible misclassification of the channels as TRIC-A, and without potential distortion of functional properties by detergent purification protocols. The native TRIC-B channels were ideally selective for cations. In symmetrical 210 mM K(+), the maximum (full) open channel level (199 pS) was equivalent to that observed when wild-type SR vesicles were incorporated into bilayers. Analysis of TRIC-B gating revealed complex and variable behaviour. Four main sub-conductance levels were observed at approximately 80 % (161 pS), 60 % (123 pS), 46 % (93 pS), and 30 % (60 pS) of the full open state. Seventy-five percent of the channels were voltage sensitive with Po being markedly reduced at negative holding potentials. The frequent, rapid transitions between TRIC-B sub-conductance states prevented development of reliable gating models using conventional single-channel analysis. Instead, we used mean-variance plots to highlight key features of TRIC-B gating in a more accurate and visually useful manner. Our study provides the first biophysical characterisation of native TRIC-B channels and indicates that this channel would be suited to provide counter current in response to Ca(2+) release from the SR. Further experiments are required to distinguish the distinct functional properties of TRIC-A and TRIC-B and understand their individual but complementary physiological roles.
authors.affiliation: School of Physiology & Pharmacology, NSQI and Bristol Heart Institute, University of Bristol, Bristol, BS8 1TD, UK.
authors.forename: Elisa
authors.initials: E
authors.lastname: Venturi
authors.forename: Antoni
authors.initials: A
authors.lastname: Matyjaszkiewicz
authors.forename: Samantha J
authors.initials: SJ
authors.lastname: Pitt
authors.forename: Krasimira
authors.initials: K
authors.lastname: Tsaneva-Atanasova
authors.forename: Miyuki
authors.initials: M
authors.lastname: Nishi
authors.forename: Daiju
authors.initials: D
authors.lastname: Yamazaki
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Takeshima
authors.forename: Rebecca
authors.initials: R
authors.lastname: Sitsapesan
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D015640:Ion Channel Gating / Q000235:genetics / Q000502:physiology*; D007473:Ion Channels / Q000235:genetics* / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology; D011188:Potassium / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000235:genetics / Q000378:metabolism / Q000502:physiology
chemical_list: D007473:Ion Channels; C522221:TRIC-A protein, mouse; C522222:TRIC-B protein, mouse; D011188:Potassium; D002118:Calcium