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. 2008 Dec 23;18(24):1955–1960. doi: 10.1016/j.cub.2008.10.067

Figure 4.

Figure 4

ShakB(N+16) and ShakB(L) Form Heterotypic Channels that Are Asymmetrically Gated by Voltage, Whereas Homotypic Channels Exhibit Symmetrical Voltage Responses

Xenopus oocytes injected with shakB RNAs were paired and recorded by dual voltage clamp. Both cells of a pair were clamped at a holding potential of −80 mV. Transjunctional voltage steps (Vj, mV) were then applied to one cell while the current (Ij, nA) required to maintain the other cell at the holding potential was recorded. Junctional conductance (Gj, μS) is Ij/Vj.

(A–E) Heterotypic cell pairs.

(A–C) Representative traces from cell pairs injected with 0.25 ng RNA. Junctional currents (A and C) were elicited by application of Vj steps (B) to (A) the ShakB(N+16)-expressing cell or (C) the ShakB(L)-expressing cell. Gj is shown for depolarizing (below baseline) and hyperpolarizing (above baseline) 10 mV steps. Mean values are provided in Table S3.

(D–E) Gj/Vj plots. Initial (open symbols) and steady-state (closed symbols) Gjs recorded in response to application of Vj steps to (D) the ShakB(N+16)-expressing cell or (E) the ShakB(L)-expressing cell. Gjs, normalized to their values at −10 mV (D) and 10 mV (E), are mean ± SD for n = 4 pairs injected with 0.1–0.25 ng RNA. Steady-state data are fitted to a Boltzmann equation (parameters in Table S3). Heterotypic channels respond asymmetrically to applied voltage.

(F–J) Homotypic cell pairs.

(F–H) Typical recordings and Gj/Vj plots (I and J) for oocyte pairs in which both cells expressed (F and I) ShakB(N+16) (0.5–2 ng RNA) or (H and J) ShakB(L) (0.05–0.25 ng RNA). (F and H) Gj is shown for depolarizing and hyperpolarizing 10 mV steps. (I and J) Initial (open symbols) and steady-state (closed symbols) Gjs normalized to their values at Vj = ±10 mV are mean ± SD for n = 8 (I) and n = 3 (J) pairs. Curves in (J) are Boltzmann fits of the data. ShakB(N+16) channels show no significant voltage sensitivity. ShakB(L) channels exhibit a symmetrical response to applied voltage. Mean Gjs and Boltzmann parameters are in Table S3.