Figure 4.

G-Proteins are involved in MiI of nAChRs currents in adrenal chromaffin cells. (a) Intracellular GTP-γ-S inhibited nAChRs currents. Left panel, rundown of whole-cell currents induced by Nic (100 μM). Middle panel, intracellular whole-cell dialysis (Rs = 11 MΩ, Cm = 14 pF) of GTP-γ-S (100 µM) for 8 min inhibited 72% of nAChRs (cell 2). Right panel, statistics of GTP-γ-S experiments. The GTP-γ-S inhibition of nAChRs is significant (p < 0.01). (b) GDP-ß-S removed MiI of nAChRs. Left panel shows that 5 µM MCh inhibited 35% of nAChRs under perforated whole-cell mode at –70 mV (cell 3). Middle panel, intracellular whole-cell dialysis (average Rs = 12, Cm = 12 pF) of GDP-ß-S (1 mM) for 8 min removed 5 µM MCh-inhibition to 10% (cell 4). Right panel, statistics of GDP-ß-S experiments. The effect of GDP-β-S on the MiI was significant (p < 0.01). (c) Effects of pertussis toxin (PTX) on MiI. PTX removed partial MiI of nAChRs under perforated whole-cell mode at –70 mV. Left two panels show that, after PTX treatment (150 ng ml⁻¹ for overnight), MCh (5 µM) inhibition was reduced from 35% (left, cell 1) to 16% (middle, cell 2). Right panel, statistics of PTX experiments. On average, PTX removed MCh (5 µM) inhibition of nAChRs significantly from 34 ± 2% to 20 ± 3% (p < 0.01). (d) Effects of BAPTA on MiI. Left three panels show that, after intracellular dialysis of 20 mM BAPTA for 10 min, 5 µM MCh-inhibition was reduced from 34% (left first panel) to 21% (left second panel). The MiI was further reduced to 12% by combined PTX and intracellular dialysis of 20 mM BAPTA (left third pane). Right panel, statistics of BAPTA experiments. On average, BAPTA and BAPTA + PTX-treatment reduced 5 µM MCh-inhibition of nAChRs significantly from to 34 ± 2% to 21 ± 3% (p < 0.01) and 12 ± 2% (p < 0.01), respectively.