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Facilitation by the β 2a subunit of pore openings in cardiac Ca 2+ channels
Author(s) -
Costantin James,
Noceti Francesca,
Qin Ning,
Wei Xiangyang,
Birnbaumer Lutz,
Stefani Enrico
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.093bu.x
Subject(s) - gating , protein subunit , xenopus , biophysics , depolarization , chemistry , r type calcium channel , physics , biology , calcium channel , biochemistry , calcium , t type calcium channel , gene , organic chemistry
1 Single channel recordings were performed on the cardiac calcium channel (α 1C ) in order to study the effect of coexpression of the accessory β 2a subunit. On‐cell patch clamp recordings were performed after expression of these channels in Xenopus oocytes. 2 The α 1C subunit, when expressed alone, had similar single channel properties to native cardiac channels. Slow transitions between low and high open probability ( P o ) gating modes were found as well as fast gating transitions between the open and closed states. 3 Coexpression of the β 2a subunit caused changes in the fast gating during high P o mode. In this mode, open time distributions reveal at least three open states and the β 2a subunit favours the occupancy of the longest, 10‐15 ms open state. No effect of the β 2a subunit was found when the channel was gating in the low P o mode. 4 Slow gating transitions were also affected by the β 2a subunit. The high P o mode was maintained for the duration of the depolarizing pulse in the presence of the β 2a subunit; while the α 1C channel when expressed alone, frequently switched into and out of the high P o mode during the course of a sweep. 5 The β 2a subunit also affected mode switching that occurred between sweeps. Runs analysis revealed that the α 1C subunit has a tendency toward non‐random mode switching. The β 2a subunit increased this tendency. A χ 2 analysis of contingency tables indicated that the β 2a subunit caused the α 1C channel to gain ‘intrinsic memory’, meaning that the mode of a given sweep can be non‐independent of the mode of the previous sweep. 6 We conclude that the β 2a subunit causes changes to the α 1C channel in both its fast and slow gating behaviour. The β 2a subunit alters fast gating by facilitating movement of the channel into an existing open state. Additionally, the β 2a subunit decreases the slow switching between low and high P o modes.