Adrenergic modulation of intracellular pH in isolated brown fat cells from hamster and rat

Abstract

The activity of the uncoupling protein in brown fat mitochondria is enhanced at alkaline pH, leading to the hypothesis that changes in intracellular pH (pHi) may modulate the thermogenic response to sympathetic stimulation. We employed ratio imaging of the fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein to measure pHi in acutely isolated single brown fat cells from hamster and neonatal rat and in cultured rat cells. Basal pHi averaged approximately 7.2 in HCO3- media and 0.1-0.15 pH units lower in nominally HCO3(-)-free media in all cell types. In both HCO3- and HCO3(-)-free media, stimulation with norepinephrine (NE) typically caused an alkalinization of approximately 0.05-0.1 pH units, which was followed by a smaller net acidification occurring primarily after NE was removed. Alkalinization seemed to be mediated predominantly by alpha-adrenergic stimulation, while acidification most often followed beta-adrenergic activation. Similar pHi changes were elicited by NE in rat and hamster cells, but responses were more frequent in hamster cells. Assays of recovery from ammonium prepulse-induced acid loads indicated that rat and hamster cells have both Na(+)-H+ and Na(+)- and HCO3(-)-dependent regulatory systems, while hamster cells have, in addition, a Na(+)-independent recovery mechanism activated at acid pHi. We conclude that alpha-adrenergic alkalinization of brown fat may contribute to the control of thermogenesis.

ZnO nanowires: chemical growth, electrodeposition, and application to intracellular nano‐sensors

“…A typical experiment measurement requires approximately five minutes. In this work, we find the measured pH value (6.81) to be close to reported values for intracellular pH (6.95-7.57) in rat brown adipocytes [84] or (6.85-7.05) in rat hepatocytes [85], using indirect determination of pH. The viability of the penetrated cells depends strongly on the size of the ZnO nanowires.…”

“…control of cellular function [80,81]. There is especially a hibiting more or less distinct pH optima.…”

MCT1 and MCT4 Expression and Lactate Flux Activity Increase During White and Brown Adipogenesis and Impact Adipocyte Metabolism

“…In accordance with this, adipocyte differentiation was associated with strongly increased expression of the Na + ,HCO 3 − cotransporter NBCe1. Several functional roles can be envisaged for the high expression of NBCe1 in differentiated adipocytes: Firstly, the above-mentioned major inhibitory effect of acidic pH i on PFK-1 24 and the inhibitory effect of acidic pH i on UCP1 function 37,38 suggest that adipocytes likely require increased capacity for net acid extrusion upon differentiation. Second, HCO 3 − is important for adipocyte function beyond its role in pH i regulation, because of its involvement as a substrate in de novo lipogenesis (in the mitochondrial production of oxaloacetate to form citrate, and in the cytosolic formation of malonyl-CoA from acetyl-CoA), in a process is dependent on CAII 39 .…”

Alpha-adrenergic stimulation activates a calcium-sensitive chloride current in brown fat cells.

“…Modulation by additional factors has been a frequently observed feature of calcium-activated chloride conductances. Candidate modulators elicited by adrenergic stimulation of brown fat include cytoplasmic alkalinization (Giovannini et al, 1988;Lee, Hamilton, Trammell, Horwitz, and Pappone, 1994) and activation of protein kinase C (Schimmel, Dzierzanowski, Elliott, and Honeyman, 1986). We have not determined whether intracellular pH modulates the conductance, but experiments switching between bath solutions with and without CO2 strongly affected the level of Ict,c~ activation in brown fat (not shown), suggesting that this may be the case.…”

“…The activation of [3-adrenergic pathways mobilizes fatty acids and uncouples mitochondria through activation of a brown fat-specific mitochondrial protein, leading to as much as 40fold increases in heat production within a few minutes of stimulation. Other immediate responses of sympathetic stimulation are mediated by the 0t-adrenergic receptors also present in the tissue, and include changes in the membrane electrical potential (Girardier and Schneider-Picard, 1983;Horwitz and Hamilton, 1984) and ion fluxes (SchneideroPicard, Coles, and Girardier, 1985;Dasso, ConnoUy, and Nedergaard, 1990) across the cell membrane, cytoplasmic alkalinization (Giovannini, Seydoux, and Girardier, 1988;Lee, Hamilton, Trammell, Horwitz, and Pappone, 1994), and increases in intracellular free calcium levels through release from intracellular stores and plasma membrane fluxes (Lee, Nuccitelli, and Pappone, 1993). Long-term stimulation of brown fat in vivo induces tissue growth, as a result of increases in both the number of brown fat cells and their size.…”