Charade of the SR K+-channel: two ion-channels, TRIC-A and TRIC-B, masquerade as a single K+-channel.

Journal article

The presence of a sarcoplasmic reticulum (SR) K+-selective ion-channel has been known for >30 years yet the molecular identity of this channel has remained a mystery. Recently, an SR trimeric intracellular cation channel (TRIC-A) was identified but it did not exhibit all expected characteristics of the SR K+-channel. We show that a related SR protein, TRIC-B, also behaves as a cation-selective ion-channel. Comparison of the single-channel properties of purified TRIC-A and TRIC-B in symmetrical 210 mM K+ solutions, show that TRIC-B has a single-channel conductance of 138 pS with subconductance levels of 59 and 35 pS, whereas TRIC-A exhibits full- and subconductance open states of 192 and 129 pS respectively. We suggest that the K+-current fluctuations observed after incorporating cardiac or skeletal SR into bilayers, can be explained by the gating of both TRIC-A and TRIC-B channels suggesting that the SR K+-channel is not a single, distinct entity. Importantly, TRIC-A is regulated strongly by trans-membrane voltage whereas TRIC-B is activated primarily by micromolar cytosolic Ca2+ and inhibited by luminal Ca2+. Thus, TRIC-A and TRIC-B channels are regulated by different mechanisms, thereby providing maximum flexibility and scope for facilitating monovalent cation flux across the SR membrane.

Authors: Pitt, S; Park, K; Nishi, M; Urashima, T; Aoki, S

• Publication status: Published
• Journal: Biophysical journal
• Volume: 99
• Issue: 2
• Pages: 417-426
• Publication date: 2010-07-01
• DOI: 10.1016/j.bpj.2010.04.051
• EISSN: 1542-0086
• ISSN: 0006-3495
• Language: English
• Keywords: Animals; Rabbits; Calcium; Myocardium; Electric Conductivity; Sheep; Potassium Chloride; Sarcoplasmic Reticulum; Cell Membrane Permeability; Ion Channel Gating; Potassium Channels; Muscle, Skeletal