Figure 3. PP2 decreases and prevents ISO stimulation of I_f.

(A) I_f currents elicited by 1-second pulses from −50 mV to −120 mV in 10 mV increments. The holding potential was −30 mV. The inset shows that I_f current was not blocked by 2 mM Ba²⁺, but by 1 mM Cs⁺ or 2 μM ZD7288. (B) I_f activation curve constructed from tail currents averaged from 7 cells. (C) I_f activation kinetics averaged from 7 cells. (D) At −100 mV, I_f (dark line, control) was unaffected by PP3 (gray line) but significantly decreased by PP2 (gray line). Washout of PP2 increased I_f (dark line). (E) At −95 mV, I_f (control) was increased by ISO, but decreased in the presence of ISO and PP2 (gray line). (F) activation curves for I_f (Control), in response to ISO and ISO+PP2 (gray line), respectively.