An ATP-sensitive K+ conductance in dissociated neurones from adult rat intracardiac ganglia
1. An ATP-sensitive K+ (KATP) conductance has been identified using the perforated patch recording configuration in a population (52%) of dissociated neurones from adult rat intracardiac ganglia. The presence of the sulphonylurea receptor in approximately half of the intracardiac neurones was confirmed by labelling with fluorescent glibenclamide-BODIPY. 2. Under current clamp conditions in physiological solutions, levcromakalim (10 μM) evoked a hyperpolarization, which was inhibited by the sulphonylurea drugs glibenclamide and tolbutamide. 3. Under voltage clamp conditions in symmetrical (140 mM) K+ solutions, bath application of levcromakalim evoked an inward current with a density of ∼8 pA pF-1 at -50 mV and a slope conductance of ∼9 nS, which reversed close to the potassium equilibrium potential (EK). Cell dialysis with an ATP-free intracellular solution also evoked an inward current, which was inhibited by tolbutamide. 4. Bath application of either glibenclamide (10 μM) or tolbutamide (100 μM) depolarized adult intracardiac neurones by 3-5 mV, suggesting that a KATP conductance is activated under resting conditions and contributes to the resting membrane potential. 5. Activation of a membrane current by levcromakalim was concentration dependent with an EC50 of 1.6 μM. Inhibition of the levcromakalim-activated current by glibenclamide was also concentration dependent with an IC50 of 55 nM. 6. Metabolic inhibition with 2,4-dinitrophenol and iodoacetic acid or superfusion with hypoxic solution (PO2 ∼16 mmHg) also activated a membrane current. These currents exhibited similar I-V characteristics to the levcromakalim-induced current and were inhibited by glibenclamide. 7. Activation of KATP channels in mammalian intracardiac neurones may contribute to changes in neural regulation of the mature heart and cardiac function during ischaemia-reperfusion.