Potassium Channel Openers Are Uncoupling Protonophores: Implication in Cardioprotection

Excessive build-up of mitochondrial protonic potential is harmful to cellular homeostasis, and modulation of inner membrane permeability a proposed countermeasure. Here, we demonstrate that structurally distinct potassium channel openers, diazoxide and pinacidil, facilitated transmembrane proton translocation generating H(+)-selective current through planar phospholipid membrane. Both openers depolarized mitochondria, activated state 4 respiration and reduced oxidative phosphorylation, recapitulating the signature of mitochondrial uncoupling. This effect was maintained in K(+)-free conditions and shared with the prototypic protonophore 2,4-dinitrophenol. Diazoxide, pinacidil and 2,4-dinitrophenol, but not 2,4-dinitrotoluene lacking protonophoric properties, preserved functional recovery of ischemic heart. The identified protonophoric property of potassium channel openers, thus, implicates a previously unrecognized component in their mechanism of cardioprotection.