The expression of membrane ionic currents in rat cortical astrocytes was investigated with the patch-clamp technique in control condition and after short term (4-24 hours) or long term (1-3 weeks) treatment of the cultures with 250 microM dibutyryl-cyclic-AMP. Outward sustained time- and voltage-dependent potassium (K+) currents were evoked by depolarizations above -40 mV in control astrocytes and in both short and long term treated cultures. They were partially blocked by extracellular application of 10 mM TEA and the current density remained unchanged in all the three experimental conditions. In contrast, time- and voltage- dependent inward currents elicited by hyperpolarizations from an holding potential of -60 mV and induced by the activation of two different conductances were recorded only in long term treatd astrocytes. The first one was associated to the activation of an inwardly rectifying K+ conductance because 1) it displayed a quasi instantaneous activation kinetic and for membrane potentials lower than -120 mV showed a time- and voltage-dependent inactivation; 2) it was reversibly blocked by extracellular 0.1 mM Ba2+; 3) the reversal potential of the currents changed in function of the extracellular K+ concentration and went along with an increase of the conductive property. The seconf had a slower activation time course and did not inactivate even for large hyperpolarizations. It was not affected by 0.1 mM Ba2+ and by the change of intra- and extracellular monovalent cations content but was sensible to the change of chloride ions and thus was identified as a chloride conductance. These two conductances might be involved in the process of the extracellular K+ buffe ring via the mechanism of the “local accumulation”.
Different expression of membrane conductances in cultured rat cortical astrocytes induced by intracellular cyclic-AMP elevation
MARCHINI, Cristina;
1995-01-01
Abstract
The expression of membrane ionic currents in rat cortical astrocytes was investigated with the patch-clamp technique in control condition and after short term (4-24 hours) or long term (1-3 weeks) treatment of the cultures with 250 microM dibutyryl-cyclic-AMP. Outward sustained time- and voltage-dependent potassium (K+) currents were evoked by depolarizations above -40 mV in control astrocytes and in both short and long term treated cultures. They were partially blocked by extracellular application of 10 mM TEA and the current density remained unchanged in all the three experimental conditions. In contrast, time- and voltage- dependent inward currents elicited by hyperpolarizations from an holding potential of -60 mV and induced by the activation of two different conductances were recorded only in long term treatd astrocytes. The first one was associated to the activation of an inwardly rectifying K+ conductance because 1) it displayed a quasi instantaneous activation kinetic and for membrane potentials lower than -120 mV showed a time- and voltage-dependent inactivation; 2) it was reversibly blocked by extracellular 0.1 mM Ba2+; 3) the reversal potential of the currents changed in function of the extracellular K+ concentration and went along with an increase of the conductive property. The seconf had a slower activation time course and did not inactivate even for large hyperpolarizations. It was not affected by 0.1 mM Ba2+ and by the change of intra- and extracellular monovalent cations content but was sensible to the change of chloride ions and thus was identified as a chloride conductance. These two conductances might be involved in the process of the extracellular K+ buffe ring via the mechanism of the “local accumulation”.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
