Figure 3. The mouse β3a subunit produces... | Rockefeller University Press

Figure 3.

$Figure 3. The mouse β3a subunit produces a use-dependent tail current enhancement similar to hβ3a, but mβ3a inactivation is more rapid and more complete. (A) Currents arising from α+mβ3a subunits were activated by the indicated protocol. (B) Currents resulting from α+hβ3a subunits show slower and more incomplete inactivation. Currents in both A and B were activated by the indicated voltage protocols with 10 μM cytosolic Ca2+. (C) Inactivation time constants measured over a range of potentials are displayed for both hβ3a and mβ3a. (D) Currents arising from channels containing either mouse β3a subunits (top) or human β3a subunits (bottom) are displayed on a slower time base to emphasize the slow tail currents. Currents were activated by the indicated voltage protocol with 10 μM Ca2+. Control currents are in red, while currents following brief application of 0.1 mg/ml trypsin are in black. Trypsin removes inactivation and the slow tail currents. (E) Activation steps of differing duration to +180 mV were used to elicit α+mβ3a currents with 10 μM Ca2+. As the command step duration is increased, the tail current switches from exclusively fast deactivating to slow deactivating. Intermediate duration command steps elicit tail currents containing distinct slow and fast time constants. Below, a brief (black, τf) and more prolonged (red, τs) step are compared emphasizing the differences in tail currents in each case. (F) The fraction of slow time constant (τs: red circles) as a function of command step duration is plotted along with the time course of inactivation onset, showing the close correlation of the two. In G, the temporal development of the slow component of tail current is compared for mouse (red circles) and human (black circles) β3a subunits.$

The mouse β3a subunit produces a use-dependent tail current enhancement similar to hβ3a, but mβ3a inactivation is more rapid and more complete. (A) Currents arising from α+mβ3a subunits were activated by the indicated protocol. (B) Currents resulting from α+hβ3a subunits show slower and more incomplete inactivation. Currents in both A and B were activated by the indicated voltage protocols with 10 μM cytosolic Ca²⁺. (C) Inactivation time constants measured over a range of potentials are displayed for both hβ3a and mβ3a. (D) Currents arising from channels containing either mouse β3a subunits (top) or human β3a subunits (bottom) are displayed on a slower time base to emphasize the slow tail currents. Currents were activated by the indicated voltage protocol with 10 μM Ca²⁺. Control currents are in red, while currents following brief application of 0.1 mg/ml trypsin are in black. Trypsin removes inactivation and the slow tail currents. (E) Activation steps of differing duration to +180 mV were used to elicit α+mβ3a currents with 10 μM Ca²⁺. As the command step duration is increased, the tail current switches from exclusively fast deactivating to slow deactivating. Intermediate duration command steps elicit tail currents containing distinct slow and fast time constants. Below, a brief (black, τ_f) and more prolonged (red, τ_s) step are compared emphasizing the differences in tail currents in each case. (F) The fraction of slow time constant (τ_s: red circles) as a function of command step duration is plotted along with the time course of inactivation onset, showing the close correlation of the two. In G, the temporal development of the slow component of tail current is compared for mouse (red circles) and human (black circles) β3a subunits.