Charade of the SR K+-Channel: Two Ion-Channels, TRIC-A and TRIC-B, Masquerade as a Single K+-Channel
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ID: 272949
2010
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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.
| Reference Key |
sitsapesan2010biophysicalcharade
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| Authors | Samantha J. Pitt,Ki-Ho Park,Miyuki Nishi,Toshiki Urashima,Sae Aoki,Daijyu Yamazaki,Jianjie Ma,Hiroshi Takeshima,Rebecca Sitsapesan;Samantha J. Pitt;Ki-Ho Park;Miyuki Nishi;Toshiki Urashima;Sae Aoki;Daijyu Yamazaki;Jianjie Ma;Hiroshi Takeshima;Rebecca Sitsapesan; |
| Journal | Biophysical journal |
| Year | 2010 |
| DOI |
10.1016/j.bpj.2010.04.051
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