Current profiles of astrocytes from the corpus callosum of newborn and 28-day-old rats.

In astrocytes, ion currents are predominantly carried by K(+) ions, and their potassium channel expression changes during development. Here, we studied ion current generated by voltage-ramp protocols in cultured astrocytes from the corpus callosum of newborn (P0) and 28-day-old (P28) rats. Inward currents measured at -140 mV and chord conductances measured from -140 to -75 mV, were smaller in P0-astrocytes than in P28-astrocytes, and in P28-astrocytes were affected by 100 μM Ba(2+), indicating the presence of an inward rectifier K(+) (Kir) current. On the other hand, P0-astrocytes showed higher outward current measured at 80 mV and a higher chord conductance, between 0 and 80 mV, than P28-astrocytes. The outward current was more potently reduced by 2mM Ba(2+) in P0-astrocytes than in P28-astrocytes, and slightly reduced at both ages using low concentrations of Ba(2+). Moreover, outward current was partially blocked by iberiotoxin in P0-astrocytes, indicating the presence of big-conductance Ca(2+)-activated K(+) (BK) channels. In addition, 4-aminopyridine inhibited the outward current in P0- and P28-astrocytes. In summary, P0-astrocytes exhibited the BK current, a major density of delayed rectifier K(+) (K(DR)) current, and a low density of the Kir current, whereas P28-astrocytes presented a major density of Kir current, a low density of the K(DR) current, and the absence of BK current. These results could contribute to a better understanding of the role of K(+) currents in the corpus callosum.