TABLE 1

Calculated Ki values for inhibition of choline-induced currents by TBuA and corticosterone. Choline-induced currents were measured in the presence of various concentrations of TBuA or corticosterone at the extracellular and intracellular sides of the membrane, and the apparent inhibitor constants (Ki values) were calculated as described under Materials and Methods and Results. The Ki values for extracellular inhibitors were determined either from the currents induced by extracellular choline (cis-inhibition) or from the currents induced by intracellular choline (trans-inhibition). The Ki values for intracellular inhibitors were calculated using the currents induced by intracellular choline (cis-inhibition). The choline concentrations employed are indicated in parenthesis (in millimolar).

Inhibitor and Application -50 mV 0 mV
cis-Inhibition trans-Inhibition cis-Inhibition trans-Inhibition
μM (mM) μM (mM) μM (mM) μM (mM)
TBuA
   Extracellular 2.5 ± 0.2 (0.2) 3.5 ± 0.5 (10) 12.5 ± 2.8 (0.2) 6.5 ± 0.4 (10)
3.3 ± 0.3 (10) 8.8 ± 0.6 (10)
   Intracellular N.D. N.D. 42 ± 13 (1) N.D.
48 ± 7.1 (10)
Corticosterone
   Extracellular 6-9 (0.2) 0.24 ± 0.06 (10) 19.5-25 (0.2) 1.08 ± 0.18 (10)
   Intracellular 0.48 ± 0.06 (1) N.D. 0.96 ± 0.33 (1) N.D.
  • N.D., not determined.