Triphenylmethylphosphonium cation distribution as a measure of hormone-induced alterations in white adipocyte membrane potential

Summary Triphenylmethylphosphonium (TPMP⁺) partitions into the mitochondrial and cytosolic compartments in the rat white adipocyte in a potential-dependent fashion. The relationship between ³H]TPMP⁺ distribution, intracellular cAMP generation and lipolysis in response to hormones and cAMP-mimetic compounds was examined. Half-maximal ³H]TPMP⁺ efflux and glycerol release were produced by 15 and 9nm adrenocorticotropin, 170 and 110nm 1-epinephrine, 70 and 27 m isobutylmethylxanthine and 800 and 750 m dibutyryl cAMP, respectively. Hormone-stimulated cAMP generation was also correlated with ³H]TPMP⁺ efflux and lipolysis in terms of concentration dependency. In kinetic experiments, glycerol release and ³H]TPMP⁺ efflux in response to adrenocorticotropin or cholera toxin proceeded over a similar time course, whereas an earlier rise in cAMP generation was detected.The depolarizing effect of lipolytic compounds was localized to the mitochondrial compartment. When cells were incubated in elevated-K⁺] _c buffer, the stimulatory effect of dibutyryl cAMP on ³H]TPMP⁺ efflux and lipolysis persisted, suggesting that maintenance of the plasma membrane potential is not critical for demonstration of these responses.When the extracellular concentration of serum albumin, which provides binding sites for free fatty acids, was increased from 1 to 3% an increase in glycerol release and a decrease in ³H]TPMP⁺ efflux was observed. We suggest that intracellular free fatty acid accumulation in response to lipolytic agents causes dissipation of the mitochondrial membrane potential and efflux of ³H]TPMP⁺ from the organelle and cell.