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

S J Pitt, K-H Park, M Nishi, T Urashima, S Aoki, D Yamazaki, J Ma, H Takeshima, R Sitsapesan

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Abstract

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.
Translated title of the contributionCharade of the SR K+-channel: two ion-channels, TRIC-A and TRIC-B, masquerade as a single K+-channel
Original languageEnglish
Pages (from-to)417 - 426
Number of pages10
JournalBiophysical Journal
Volume99
DOIs
Publication statusPublished - Jul 2010

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    Pitt, S. J., Park, K-H., Nishi, M., Urashima, T., Aoki, S., Yamazaki, D., Ma, J., Takeshima, H., & Sitsapesan, R. (2010). Charade of the SR K+-channel: two ion-channels, TRIC-A and TRIC-B, masquerade as a single K+-channel. Biophysical Journal, 99, 417 - 426. https://doi.org/10.1016/j.bpj.2010.04.051