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Casas M, Buvinic S, Jaimovich E.
Exerc Sport Sci Rev. 2014 Jul;42(3):110-6. doi: 10.1249/JES.0000000000000017. Review.
Abstract
Tetanic electrical stimulation releases adenosine triphosphate (ATP) from muscle fibers through pannexin-1 channels
in a frequency-dependent manner; extracellular ATP activates signals
that ultimately regulate gene expression and is able to increase glucose
transport through activation of P2Y receptors, phosphatidylinositol
3-kinase, Akt, and AS160. We hypothesize that this mechanism is an
important link between exercise and the regulation of muscle fiber
plasticity and metabolism.
Orellana
JA, Sáez PJ, Cortés-Campos C, Elizondo RJ, Shoji KF, Contreras-Duarte
S, Figueroa V, Velarde V, Jiang JX, Nualart F, Sáez JC, García MA.
Glia. 2012 Jan;60(1):53-68. doi: 10.1002/glia.21246.
Abstract
The
ventromedial hypothalamus is involved in regulating feeding and satiety
behavior, and its neurons interact with specialized ependymal-glial
cells, termed tanycytes. The latter express glucose-sensing proteins, including glucose transporter 2, glucokinase, and ATP-sensitive K(+) (K(ATP) ) channels, suggesting their involvement in hypothalamic glucosensing. Here, the transduction mechanism involved in the glucose-induced
rise of intracellular free Ca(2+) concentration ([Ca(2+) ](i) ) in
cultured β-tanycytes was examined. Fura-2AM time-lapse fluorescence
images revealed that glucose increases the intracellular Ca(2+) signal in a concentration-dependent manner. Glucose transportation, primarily via glucose transporters, and metabolism via anaerobic glycolysis increased connexin
43 (Cx43) hemichannel activity, evaluated by ethidium uptake and whole
cell patch clamp recordings, through a K(ATP) channel-dependent pathway.
Consequently, ATP export to the extracellular milieu was enhanced,
resulting in activation of purinergic P2Y(1) receptors followed by inositol
trisphosphate receptor activation and Ca(2+) release from intracellular
stores. The present study identifies the mechanism by which glucose
increases [Ca(2+) ](i) in tanycytes. It also establishes that Cx43
hemichannels can be rapidly activated under physiological conditions by
the sequential activation of glucosensing proteins in normal tanycytes.
Copyright © 2011 Wiley Periodicals, Inc.
Niessen H, Harz H, Bedner P, Krämer K, Willecke K.
J Cell Sci. 2000 Apr;113 ( Pt 8):1365-72.
Abstract
Intercellular
propagation of signals through connexin32-containing gap junctions is
of major importance in physiological processes like nerve
activity-dependent glucose
mobilization in liver parenchymal cells and enzyme secretion from
pancreatic acinar cells.
In these cells, as in other organs, more than one type of connexin is expressed.
We hypothesized that different permeabilities towards second messenger molecules could be one of the reasons for connexin diversity. In order to investigate this, we analyzed transmission of inositol 1,4,5-trisphosphate-mediated calcium waves in FURA-2-loaded monolayers of human HeLa cells expressing murine connexin26, -32 or -43. Gap junction-mediated cell coupling in different connexin-transfected HeLa cells was standardized by measuring the spreading of microinjected Mn(2+) that led to local quenching of FURA-2 fluorescence. Microinjection of inositol 1,4,5-trisphosphate into confluently growing HeLa connexin32 transfectants induced propagation of a Ca(2+) wave from the injected cell to neighboring cells that was at least three- to fourfold more efficient than in HeLa Cx26 cells and about 2.5-fold more efficient than in HeLa Cx43 transfectants. Our results support the notion that diffusion of inositol 1,4,5-trisphosphate through connexin32-containing gap junctions is essential for the optimal physiological response, for example by recruiting liver parenchymal cells that contain subthreshold levels of this short lived second messenger.
In these cells, as in other organs, more than one type of connexin is expressed.
We hypothesized that different permeabilities towards second messenger molecules could be one of the reasons for connexin diversity. In order to investigate this, we analyzed transmission of inositol 1,4,5-trisphosphate-mediated calcium waves in FURA-2-loaded monolayers of human HeLa cells expressing murine connexin26, -32 or -43. Gap junction-mediated cell coupling in different connexin-transfected HeLa cells was standardized by measuring the spreading of microinjected Mn(2+) that led to local quenching of FURA-2 fluorescence. Microinjection of inositol 1,4,5-trisphosphate into confluently growing HeLa connexin32 transfectants induced propagation of a Ca(2+) wave from the injected cell to neighboring cells that was at least three- to fourfold more efficient than in HeLa Cx26 cells and about 2.5-fold more efficient than in HeLa Cx43 transfectants. Our results support the notion that diffusion of inositol 1,4,5-trisphosphate through connexin32-containing gap junctions is essential for the optimal physiological response, for example by recruiting liver parenchymal cells that contain subthreshold levels of this short lived second messenger.
