Octanol, a gap junction uncoupling agent, changes intracellular [H+] in rat astrocytes

Abstract

Octanol rapidly closes gap junction channels but its mechanism of action is not known. Because intracellular [H+], pHi, also affects the conductance of gap junctions, we studied octanol's effects on pHi in cultured rat astrocytes, which are highly coupled cells. Octanol (1 mM) caused an acid shift in the pHi of 90% of rat hippocampal astrocytes which averaged −0.19 ± 0.09 pH units in magnitude. In 58% of the cells tested, a biphasic change in pHi was seen; octanol produced an initial acidification lasting ∼10 min that was followed by a persistent alkalinization. The related gap junction uncoupling agent, heptanol, had similar effects on pHi. Octanol‐induced changes in pHi were similar in nominally HCO3−‐free and HCO3−‐containing solutions, although the rate of initial acidification was significantly greater in the presence of HCO3−. The initial acidification was inhibited in the presence of the stilbene DIDS, an inhibitor of Na+/HCO3− cotransport, indicating that octanol caused acidification by blocking this powerful acid extruder. The alkalinization was inhibited by amiloride which blocks the Na+/H+ exchanger (NHE), an acid extruder, suggesting that the alkaline shift induced by octanol was caused by stimulation of NHE. As expected, octanol's effects on astrocytic pHi were prevented by removal of external Na+, which blocks both Na+/HCO3− cotransport and NHE. Octanol had only small effects on intracellular Ca2+ (Ca2+i) in astrocytes. Hepatocytes which, like astrocytes, are strongly coupled to one another, showed no change in pHi with octanol application. Fluorescence recovery after photobleaching (FRAP) was used to study the effect of changes in astrocyte pHi on degree of coupling in hippocampal astrocytes. Coupling was decreased by intracellular acid shifts ∼−0.2 pH units in size. Octanol's effects on astrocyte pHi were complex but a prompt initial acidification was nearly always seen and could contribute to the uncoupling action of this drug in astrocytes. Because octanol uncouples hepatocytes without changing their pHi, this compound clearly can influence gap junctional conductance independent of changes in pHi. © 1996 Wiley‐Liss, Inc.

Blocking gap junctional intercellular communication in myoblasts inhibits myogenin and MRF4 expression

“…Spray and Burt [1990] have proposed a mechanism whereby the octanol molecules, being lipophilic compounds, would be incorporated into the cell membrane structure and the resulting perturbations could induce conformational changes in nearby gap junctions resulting in their closure. In a recent study by Pappas et al [1996], small variations in intracellular pH were observed in cells treated with octanol or heptanol. Such disturbances in pH are known to affect channel permeability, Fig.…”

Seasonal changes in astrocytes parallel neuronal plasticity in the song control area HVc of the canary

“…In the first control experiment, we added 200 µM octanol to the superfusate directly after penetration of a cell, prior to the start of the dye injection. Octanol is known to reduce or fully eliminate gap-junctional communication in a variety of cell types (Pappas et al, 1996;Rose and Ransom, 1997;Sontheimer et al, 1991). Analysis of the number of dye labeled cells revealed a significant reduction of transcellular dye labeling in the presence of octanol (Fig.…”

Glia-related circadian plasticity in the visual system of Diptera

“…Most of the gap junctions in the lamina are formed between glial cells (Saint Marie et al, 1984). Therefore, the uncoupling effect of the application of gap junction closing agent, such as octanol (Pappas et al, 1996), is observed predominantly on the “glial part” of the lamina. The contribution of gap junctions formed between neurons, however, cannot be entirely ruled out.…”