Ionic channels in mouse astrocytes in culture

Abstract

We observed Na, K, and Cl voltage-dependent currents in a patch-clamp study of mouse brain astrocytes. In whole-cell recordings, depolarizations activated inward currents that were identified as Na currents since they were blocked by TTX, although complete block required high concentrations (greater than 1 microM). The corresponding single-channel Na currents were observed in outside-out patches. The channels were opened by a depolarizing pulse applied from a holding potential identical to the resting potential (-70 to -80 mV). Therefore, they may be considered functional Na channels. After addition of veratridine and an alpha-scorpion toxin, the decay of Na currents in whole-cell recordings was slower than observed under control conditions. At the single-channel level, the channels appeared to open in bursts. Depolarization did not increase the duration of the bursts, but inside each burst, increased the time spent in the open state. The K currents observed in the whole-cell recording mode were separated into inactivating and noninactivating currents. The inactivating current resembled the A current in its kinetics, its insensitivity to tetraethylammonium, and its sensitivity to 4-aminopyridine. At the single-channel level, at least 3 classes of K channels were observed at steady depolarized potentials. They resembled the K channels found in chromaffin cells by Marty and Neher (1985). Large conductance channels (385 pS) activated around 0 mV were identified as Cl channels.

Two distinct inwardly rectifying conductances are expressed in long term dibutyryl‐cyclic‐AMP treated rat cultured cortical astrocytes

“…Outward sustained currents were never observed when the intracellular K + was substituted with the impermeable larger cation N-methyl-i>glucamine (NMDG ÷) (n = 8, data not shown). The findings suggest that these outward currents were due to the activation of a K ÷ channel and resemble the outward K ÷ conductance which has been described in rat and mouse cultured cortical astrocytes [23,24].…”

The maxi-anion channel: a classical channel playing novel roles through an unidentified molecular entity

“…Modified from Sabirov et al [8] 2 day old rats [18] and adult humans [47] as well as in freshly dissected rat spinal root Schwann cells [48]. These channels were similar to those observed in cultured cortical astrocytes from rats [4,49,50] and mice [5][6][7]51] as well as in a rat astrocytic RGCN cell line [52]. In epithelia, the urinary bladder [53], gastric [54], pancreatic [55][56][57], colonic [58][59][60], airway [61][62][63], choroid plexus [64], bile duct [65,66], ciliary [67][68][69], renal [9,19,[70][71][72][73][74][75][76][77][78], vestibular [79], placental [80][81][82][83][84][85][86], ruminal …”

Chloride/anion channels in glial cell membranes

“…Nowak et al (1987) first described a hyperpolarization-induced small unitary conductance channel (5 pS) in cultured astrocytes. This channel was not further studied in detail until Ferroni et al (1995) discovered that only cultured astrocytes treated for at least 1 week with dbcAMP expressed the current.…”

“…Another channel commonly found in cultured astrocytes is a large anion conductance, which has been known for quite some time (Bevan et al, 1985;Nowak et al, 1987;Sonnhof, 1987;Jalonen, 1993). It has a peculiar property of only being found in excised patches, as if an inhibitory factor prevents expression in intact cells.…”