Facilitation by the β2a subunit of pore openings in cardiac Ca2+ channels

• Published in: The Journal of physiology 1998-02, Vol.507 (1), p.93
• Main Authors: James Costantin, Francesca Noceti, Ning Qin, Xiangyang Wei, Lutz Birnbaumer, Enrico Stefani
• Format: Article
• Language: English
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1111/j.1469-7793.1998.093bu.x

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. 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. 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. 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. 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. 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.