a, Single-channel currents of purified A3/B3 activated by 10 μM cGMP. A total of 29 patches were recorded. Of them, 17 showed no cGMP activity and 12 showed cGMP-activated activity. b, Continuous trace of A3/B3 single-channel current showing inhibition by L-cis-diltiazem (DTZ). c, Amplitude histogram of cGMP-induced currents at + 80 mV from one patch. d, Single-channel conductance of cGMP-induced currents. Data were presented as mean±SD. e, Continuous trace of the same patch as in (b) showing a preference of cGMP over cAMP. f, Single-channel open probability of currents evoked by 10 μM cGMP or 10 μM cAMP. Data were presented as mean±SD.