Fig. 5.
The α2δ subunit affects current through the α1E-type calcium channel. Unless otherwise indicated, the voltage protocols used were the same as those described in the legend to Figure 4. ○ represents the α1Eβ3 channel; • the α1Eβ3α2δ-1 channel, and ▪ the α1Eβ3α2δ-3 channel. Boltzmann fits of voltage dependencies of current activation are summarized in Table 1. The inset in theright of a shows a typical family of currents measured during a series of depolarizing pulses from a holding potential of −100 mV to membrane potentials ranging from −30 mV to +60 mV with step of +10 mV. ○, α1Eβ3 channel, with a cell capacity of 19 pF and a maximal current density of approximately −34 pA/pF; ▪, α1Eβ3α2δ-3 channel, with a capacity of 43 pF and a maximal current density of approximately −74 pA/pF. b shows the steady-state inactivation curve measured from a holding potential of −100 mV using a 5-sec- long conditioning pulse to membrane potentials marked on the ordinate.Solid lines represent Boltzmann fits. Theinsert illustrates the inactivation ofIBa during a 300-msec-long depolarizing pulse from a holding potential of −100 mV to +20 mV scaled to the same amplitude. Eight to 10 measurements were averaged for each channel type. The α1Eβ3α2δ-1 and α1Eβ3α2δ-3 current traces are indistinguishable from each other. Individual time courses of current inactivation were fitted to a single exponential with a small proportion of noninactivating current. Results of all fits are summarized in Table 1. Symbols are as ina.