The Effective Proton Conductance of the Inner Membrane of Mitochondria from Brown Adipose Tissue

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Abstract
The nucleotide-sensitive H+ (OH-) conducting pathway of mitochondria from the brown adipose tissue of cold-adapted guinea pigs passes an effective proton current which is directly proportional to the proton electrochemical gradient [.DELTA..hivin..mu.H+]. At 23.degree. C and pH 7.0 this conductance is 16 nmol H+ .cntdot. min-1 .cntdot. mg-1 .cntdot. mV-1. Addition of 0.2 mM GDP results in a conductance which is linear and low (0.7 nmol H+ .cntdot. min-1 .cntdot. mg-1 mV-1) until .DELTA..hivin..mu.H+ exceeds 220 mV. At higher values of of .DELTA..hivin..mu.H+, which can be attained by glycerol 3-phosphate oxidation but not palmitoyl-L-carnitine plus malate oxidation, the membrane conductance greatly increases, effectively limiting the maximal .DELTA..hivin..mu.H+ to 240 mV. High glycerol 3-phosphate concentrations which have the thermodynamic potential to exceed this value of .DELTA..hivin..mu.H+ instead create a greatly increased rate of controlled respiration. The generality and significance of this device to limit .DELTA..hivin..mu.H+ and its relation to the nucleotide-sensitive conductance are discussed.