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

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.