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

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Abstract
Long term incubation (1–3 weeks) with 250 μM dibutyryl‐cyclic‐AMP (dBcAMP) of pure cultured cortical astrocytes from newborn rats leads to the expression of voltage‐dependent, inward‐rectifying potassium (K+) and chloride (Cl−) currents which are lacking in shortly treated (4–24 h) and in control cultured astrocytes. Both conductances are already activated at the holding potential of −60 mV and are distinguishable for their gating kinetics and pharmacological sensitivity. K+ currents have a fast activation kinetic and show a time‐ and voltage‐dependent inactivation at potentials negative to −120 mV. The conductive property of the K+ currents increases upon elevation of the extracellular K+ concentration ([K+]0) and they are reversibly blocked by extracellular 0.1 mM barium ions (Ba2+). Cl− currents are activated only at negative membrane potentials; they display a slow activation kinetic, no time‐dependent inactivation and are not affected by 0.1 mM Ba2+. In individual astrocyte the K+ and Cl− conductances can be expressed singularly or in combination. The results indicate that the expression of these two conductances is controlled by a cAMP‐dependent molecular signalling, presumably by regulating a late gene activation. Thus, the strengthening of this signalling would contribute to promote the maturation of less differentiated astrocytes in culture, implicating the expression of K+ and Cl− membrane conductances which may operate together in the regulation of [K+]0 homeostasis via the mechanism of the local accumulation.