Fig. 2.

Comparison of the effect of PMA to that of PKC. (A₁–A₆) GIRK1-GIRK4 currents were recorded from a cell-attached patch with 150 mM K⁺ applied to the extracellular solution at a membrane potential of –80 mV. Five active currents were seen at baseline with NP_o 0.671 (A₁). These currents were inhibited when the oocytes was exposed to 30 nM PMA for 10 min (NP_o 0.076, A₂). (A₃ and A₄) The single-channel currents are better seen with an expended time scale taken from A₁ and A₂ at places pointed by arrows, respectively. (A₅ and A₆) In contrast to the NP_o, single-channel conductance was inhibited only modestly by PMA. (B₁–B₆) Inhibition of the GIRK1-GIRK4 currents by purified catalytic subunit of PKC. (B₁) Single-channel currents were studied in an excised inside-out patch with 150 mM K⁺ applied to both sides of the patch membrane. Four active channels are seen at baseline with NP_o 1.143. (B₂) The channel activity was strongly inhibited (NP_o 0.144) 10 min after an exposure of the internal surface of the patch member to PKC (0.1 units/ml). (B₅ and B₆) PKC had very little effect on single-channel conductance in another inside-out patch. Note that substate conductances are seen in all records.