TABLE I.

Single Human Ca_V2.1 Channels Containing Different β Subunits Have Similar Open and Closed Time Distributions in Either the Fast or the Slow Mode of Gating

	τo1	τo2	τc1	τc2	τc3	po	i	n
Fast mode
β1b	0.63 ± 0.06	1.4 ± 0.1	0.39 ± 0.05	2.0 ± 0.3	6.7 ± 1.0	0.350 ± 0.020	0.76 ± 0.01	5
β2e	0.54 ± 0.03	1.2 ± 0.1	0.45 ± 0.02	2.4 ± 0.2	7.4 ± 0.5	0.284 ± 0.013a	0.75 ± 0.01	3
β3a	0.65 ± 0.12	1.5 ± 0.2	0.41 ± 0.04	2.1 ± 0.2	6.2 ± 0.3	0.330 ± 0.014	0.74 ± 0.01	6
β4a	0.47 ± 0.08	1.4 ± 0.04	0.33 ± 0.03	2.0 ± 0.3	6.4 ± 0.9	0.308 ± 0.040	0.73 ± 0.01	4
Slow mode
β1b	0.48 ± 0.08	1.3 ± 0.1	0.49 ± 0.08	3.8 ± 0.8	14 ± 1	0.188 ± 0.012	0.76 ± 0.01	5
β2e	0.48 ± 0.03	1.3 ± 0.1	0.56 ± 0.04	7.2 ± 2.0b	24 ± 4c	0.125 ± 0.021c	0.73 ± 0.03	4
β4a	0.56 ± 0.12	1.6 ± 0.2	0.38 ± 0.07	2.2 ± 0.8	18 ± 4	0.150 ± 0.024	0.73 ± 0.02	4

Single channel recordings as in Fig. 1 on HEK293 cells stably coexpressing human Ca_V2.1α1 (α_1A-2), α_2bδ-1, and β_1b, β_2e, β_3a, or β_4a subunits. Time constants of the exponential components best fitting the open (τ_o1 and τ_o2) and closed (τ_c1, τ_c2, and τ_c3) time distributions at +30 mV of single Ca_V2.1 channels containing different β subunits in slow and fast gating modes. Average values were obtained from single channel patches in which the channel showed only (or mainly) one gating mode or two clearly separated periods in the two modes. Average values of the open probability and the unitary current from the same patches are also shown. Most of the data for Ca_V2.1 channels containing the β_3a subunit were obtained from PB1-14 cells transfected with β_3a cDNA (given the low level of expression of β_3a subunit in this stable cell line).

^aβ_2e with respect to β_1b and β_3a, P < 0.05.

^bβ_2e with respect to β_1b and β_4a, P < 0.05.

^cβ_2e with respect to β_1b, P < 0.05.