CATION AND ANION UNITARY ION-CHANNEL CURRENTS IN CULTURED BOVINE MICROGLIA

The use of excised patches has led to the identification and character ization of two channels not previously reported in microglia. A calciu m-dependent K+ channel K(Ca) was activated in inside-out patches obtai ned from cultured bovine microglia and had a unitary conductance of 24 0 pS with symmetrical 140 mM K+ across patches. Mean open times of K(C a) were exponentially dependent on patch potential and were increased with patch depolarization. Channel open probability (Popen) was increa sed with patch depolarization with either 5 mM or 140 mM internal K+ a nd was attributable to potential dependent enhancement of both opening frequency and mean open time. Whole cell currents showed the presence of a slowly activating K+ conductance, blocked by external TEA (at 2 mM) and likely the macroscopic correlate of the unitary K(Ca); half-ma ximal activation of the current occurred at +25 mV. An anion channel ( unitary conductance of 325 pS with symmetrical Cl- across patches) was activated in inside-out patches with depolarizing and hyperpolarizing potential steps from 0 mV. Channel activation was not dependent on in ternal Ca2+. The anion currents inactivated during maintained potentia l steps with the time constant for inactivation faster with increased patch depolarization. The properties of the K(Ca) and anion channels i n microglia membrane may have relevance to cell function in response t o neuronal damage in the CNS.