Alternating hypoglycemia and hyperglycemia in a toddler with a homozygous p.R1419H ABCC8 mutation: an unusual clinical picture

Inheritance of two pathogenicSingle nucleotide polymorphism microarray and Sanger sequencing were performed. Western blot, rubidium efflux, and patch clamp recordings interrogated the expression and activity of the mutant protein.A 16-month-old girl of consanguineous descent manifested hypoglycemia. She had dysregulation of insulin secretion, with postprandial hyperglycemia followed by hypoglycemia. Microarray revealed homozygosity for the regions encompassingThis is the first description of a homozygous p.R1419H mutation. Our findings highlight that homozygous loss-of-function mutations of

Measurements of mitochondrial K+ fluxes in whole rat hearts using 87Rb-NMR

The rubidium efflux from hypothermic rat hearts perfused by the Langendorff method at 20°C was studied. At this temperature 87Rb-NMR efflux experiments showed the existence of two 87Rb pools: cytoplasmic and mitochondrial. Rat heart mitochondria showed a very slow exchange of mitochondrial Rb+ for cytoplasmic K+. After washout of cytosolic Rb+, mitochondria kept a stable Rb+level for >30 min. Rb+ efflux from mitochondria was stimulated with 0.1 mM 2,4-dinitrophenol (DNP), by sarcolemmal permeabilization and concomitant cellular energy depletion by saponin (0.01 mg/ml for 4 min) in the presence of a perfusate mimicking intracellular conditions, or by ATP-sensitive K (KATP) channel openers. DNP, a mitochondrial uncoupler, caused the onset of mitochondrial Rb+ exchange; however, the washout was not complete (80 vs. 56% in control). Energy deprivation by saponin, which permeabilizes the sarcolemma, resulted in a rapid and complete Rb+ efflux. The mitochondrial Rb+ efflux rate constant ( k) decreased in the presence of glibenclamide, a KATP channel inhibitor (5 μM; k = 0.204 ± 0.065 min−1; n = 8), or in the presence of ATP plus phosphocreatine (1.0 and 5.0 mM, respectively; k = 0.134 ± 0.021 min−1; n = 4) in the saponin experiments (saponin only; k = 0.321 ± 0.079 min−1; n = 3), indicating the inhibition of mitochondrial KATP channels. Thus hypothermia in combination with 87Rb-NMR allowed the probing of the mitochondrial K+ pool in whole hearts without mitochondrial isolation.