Fig. 4. Block of Nav1.4-wild-type (Nav1.4-WT) and mutant constructs in HEK293t cells by buprenorphine. Representative current traces of Nav1.4-WT (A ) and Nav1.4–1579°K (B ) in presence of 30 μM buprenorphine. Currents were activated at 10 Hz with 25 ms-long pulses to 50 mV (V^h= 140 mV). (C ) Development of use-dependent block of Nav1.4-WT and mutant constructs by 30 μM buprenorphine at 10 Hz. Peak currents were normalized to the current of the first pulse and plotted against the pulse number. (D ) Concentration-dependent block of Na^v1.4-WT and the mutants −1280°K, −434°K, and −1579°K by buprenorphine. Currents were activated by 5 ms-long test pulses from −140 mV to 50 mV in intervals of 20 s. Peak amplitudes of Na⁺currents at different drug concentrations were normalized with respect to the peak amplitude in control solution and plotted against the concentration of buprenorphine. Solid lines  are fits of the data with the Hill equation.