Figure 9. Dose responses for ATP... | Rockefeller University Press

Figure 9.

$Figure 9. Dose responses for ATP inhibition of channels obtained by coexpression of free SUR1, SUR2A, and Kir6.2 suggest the coassembly of free SUR1 with free SUR2A. (A) Representative current traces obtained in inside-out patches from oocytes expressing SUR1+Kir6.2 (black trace), SUR2A+Kir6.2 (blue trace), or SUR1+SUR2A+Kir6.2 (SUR1:SUR2A=1:1; red trace). The membrane was held at −100 mV and ATP at various concentrations was applied to the bath solution as indicated. (B) Fractional currents remaining in the presence of various concentrations of cytosolic ATP in patches excised from oocytes expressing SUR1+Kir6.2 (black symbols), SUR2A+Kir6.2 (blue symbols), or SUR1+SUR2A+ Kir6.2 (red symbols). Black and blue solid lines show fits to the Hill equation of the data for SUR1+Kir6.2 and SUR2A+Kir6.2, respectively. Fit parameters are listed Fig. 1 A. Red dotted and solid lines illustrate predicted curves for SUR1+SUR2A+Kir6.2 assuming that SUR1 does not coassemble with SUR2A. The red dotted line is the simple arithmetic average of the two Hill functions obtained for SUR1+Kir6.2 (black line) and SUR2A+Kir6.2 (blue line), expected if SUR1 and SUR2A protein was expressed at an equal molar ratio but did not coassemble. The red solid line is the best fit to the SUR1+SUR2A+Kir6.2 data by a mixture of the two parent Hill functions, with the fractional amplitude of channels formed from SUR1+Kir6.2, a1, left as a free parameter. This fit returned a1 = 0.69 ± 0.06, but still failed to describe the data.$

Dose responses for ATP inhibition of channels obtained by coexpression of free SUR1, SUR2A, and Kir6.2 suggest the coassembly of free SUR1 with free SUR2A. (A) Representative current traces obtained in inside-out patches from oocytes expressing SUR1+Kir6.2 (black trace), SUR2A+Kir6.2 (blue trace), or SUR1+SUR2A+Kir6.2 (SUR1:SUR2A=1:1; red trace). The membrane was held at −100 mV and ATP at various concentrations was applied to the bath solution as indicated. (B) Fractional currents remaining in the presence of various concentrations of cytosolic ATP in patches excised from oocytes expressing SUR1+Kir6.2 (black symbols), SUR2A+Kir6.2 (blue symbols), or SUR1+SUR2A+ Kir6.2 (red symbols). Black and blue solid lines show fits to the Hill equation of the data for SUR1+Kir6.2 and SUR2A+Kir6.2, respectively. Fit parameters are listed Fig. 1 A. Red dotted and solid lines illustrate predicted curves for SUR1+SUR2A+Kir6.2 assuming that SUR1 does not coassemble with SUR2A. The red dotted line is the simple arithmetic average of the two Hill functions obtained for SUR1+Kir6.2 (black line) and SUR2A+Kir6.2 (blue line), expected if SUR1 and SUR2A protein was expressed at an equal molar ratio but did not coassemble. The red solid line is the best fit to the SUR1+SUR2A+Kir6.2 data by a mixture of the two parent Hill functions, with the fractional amplitude of channels formed from SUR1+Kir6.2, a₁, left as a free parameter. This fit returned a₁ = 0.69 ± 0.06, but still failed to describe the data.