title: Etiology of the membrane potential of rat white fat adipocytes.
abstract: The plasma membrane potential (Vm) is key to many physiological processes; however, its ionic etiology in white fat adipocytes is poorly characterized. To address this question, we employed the perforated patch current clamp and cell-attached patch clamp methods in isolated primary white fat adipocytes and their cellular model 3T3-L1. The resting Vm of primary and 3T3-L1 adipocytes were -32.1 ± 1.2 mV (n = 95) and -28.8 ± 1.2 mV (n = 87), respectively. Vm was independent of cell size and fat content. Elevation of extracellular K(+) to 50 mM by equimolar substitution of bath Na(+) did not affect Vm, whereas substitution of bath Na(+) with the membrane-impermeant cation N-methyl-D-glucamine(+)-hyperpolarized Vm by 16 mV, data indicative of a nonselective cation permeability. Substitution of 133 mM extracellular Cl(-) with gluconate-depolarized Vm by 25 mV, whereas Cl(-) substitution with I(-) caused a -9 mV hyperpolarization. Isoprenaline (10 μM), but not insulin (100 nM), significantly depolarized Vm. Single-channel ion activity was voltage independent; currents were indicative for Cl(-) with an inward slope conductance of 16 ± 1.3 pS (n = 11) and a reversal potential close to the Cl(-) equilibrium potential, -29 ± 1.6 mV. Although the reduction of extracellular Cl(-) elevated the intracellular Ca(2+) of adipocytes, this was not as large as that produced by elevation of extracellular K(+). In conclusion, the Vm of white fat adipocytes is well described by the Goldman-Hodgkin-Katz equation with a predominant permeability to Cl(-), where its biophysical and single-channel properties suggest a volume-sensitive anion channel identity. Consequently, changes in serum Cl(-) homeostasis or the adipocyte's permeability to this anion via drugs will affect its Vm, intracellular Ca(2+), and ultimately its function and its role in metabolic control.
authors.affiliation: School of Life Sciences, University of Nottingham, Nottingham, United Kingdom.
authors.forename: Donna C
authors.initials: DC
authors.lastname: Bentley
authors.affiliation: School of Life Sciences, University of Nottingham, Nottingham, United Kingdom.
authors.forename: Pawitra
authors.initials: P
authors.lastname: Pulbutr
authors.affiliation: School of Life Sciences, University of Nottingham, Nottingham, United Kingdom.
authors.forename: Sue
authors.initials: S
authors.lastname: Chan
authors.affiliation: School of Life Sciences, University of Nottingham, Nottingham, United Kingdom Paul.a.smith@nottingham.ac.uk.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Smith
mesh_terms: D041721:3T3-L1 Cells; D052438:Adipocytes, White / Q000166:cytology / Q000502:physiology*; D050156:Adipogenesis / Q000502:physiology; D000818:Animals; D002454:Cell Differentiation; D048429:Cell Size; D002478:Cells, Cultured; D008297:Male; D008564:Membrane Potentials; D051379:Mice; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar
keywords: 3T3-L1 cells; adipocyte; chloride; membrane potential; white fat