Pharmacological activation of plasma-membrane KATP channels reduces reoxygenation-induced Ca2+ overload in cardiac myocytes via modulation of the diastolic membrane potential

摘要

class="enumerated" style="list-style-type:decimal">The opening of cardiac plasma-membrane ATP-sensitive K⁺ channels (pmKATP) can protect the heart against ischaemia/reperfusion injury. We recently demonstrated that the resting membrane potential (Em) of ventricular myocytes strongly modulates reoxygenation-induced Ca²⁺ overload. This led to the hypothesis that activation of pmKATP can influence the extent of chemically induced hypoxia (CIH)/reoxygenation Ca²⁺ overload via hyperpolarization of the diastolic membrane potential of ventricular myocytes.The membrane potential (Em) of isolated rat myocytes was determined using the perforated patch-clamp technique and DiBac4(3) imaging. Intracellular Ca²⁺ ([Ca²⁺]i) was monitored using FURA-2 imaging.CIH/reoxygenation caused a significant depolarization of Em and a substantial increase in [Ca²⁺]i. The KATP opener pinacidil (100 μM) and the pmKATP opener P-1075 (100 μM) hyperpolarized the Em of normoxic myocytes. Pinacidil (100 μM) and P-1075 (10 and 100 μM), applied during reoxygenation, hyperpolarized Em and prevented reoxygenation-induced increases in [Ca²⁺]i.Myocyte hypercontracture and death increased in parallel with an Em depolarization of 10–15 mV and increases in [Ca²⁺]i. Under these conditions, the selective pmKATP channel inhibitor HMR 1098 further depolarized myocyte membrane potential and increased hypercontracture.In conclusion, activation of pmK_ATP channels can prevent CIH/reoxygenation-induced Ca²⁺ overload via a mechanism that is dependent on hyperpolarization of diastolic membrane potential. Hyperpolarization toward normal resting membrane potential favours the Ca²⁺ extrusion mode of Na⁺/Ca²⁺ exchange.