The effect of polyamines on K ATP channels in guinea‐pig ventricular myocytes

1 The effect of natural polyamines on K ATP channels was studied using inside‐out patches from guinea‐pig ventricular myocytes. 2 At a holding potential of +40 mV, spermine at the intracellular membrane surface reduced the K ATP channel open probability ( P open ) in a dose‐dependent manner. Half‐maximal inhibition occurred at 29 μM with a Hill coefficient of 1.2. 3 The effect of spermine on P open was not greatly influenced by the membrane potential but there appeared to be a small reduction in unitary current amplitude during strong depolarizations. 4 Analysis of K ATP single channel kinetics showed that spermine inhibited the channel by decreasing the mean open time and introducing transitions to a long closed state. 5 Spermidine (0.1 mM) was found to have a similar effect to spermine. Putrescine (10 mM) was found to block more effectively at positive membrane potentials. Up to 20 mM arginine had no significant effect on K ATP channels. 6 Our results indicate that natural polyamines influence native K ATP channel gating in cardiac myocytes.