Figure 2.

Use-dependent inhibition of voltage-gated Na⁺ currents in β-cells from MIP-GFP dispersed islets. A, GFP-positive cells were identified by epifluorescence, and whole-cell patch clamp recording was performed. Cells were held at −100 mV and pulsed in 10-mV steps between −90 mV and +50 mV. Rapidly decaying inward Na⁺ currents were apparent, along with a sustained inward current. The rapidly decaying current component was well inhibited by carbamazepine (CBZ). B, Peak current-voltage relationships for Na⁺ currents in the presence and absence of carbamazepine. C, Current traces depict pulses 1 and 25 in a repetitive train of 20-ms depolarizations from −100 mV to +10 mV (10-Hz frequency). In the presence of carbamazepine, there is a significant tonic block of the current starting at pulse 1 and further current reduction over the course of the pulse train. The sustained current component was not sensitive to use-dependent inhibition. D, Dispersed MIP-GFP islet cells were FACS sorted, and the expression of voltage-gated Na⁺ channels (Na_v) and β-subunits (Na_vβ) was detected by quantitative RT-PCR (n = 3, mean ± SEM).