Passive electrical properties of presumed astrocytes from hyperglycemic and ischemic brain. A: Membrane potential in “real time.” B: Bridge balance records made at specific times (Le., a, b, c in A). Records are interpreted as follows. First, bridge was balanced (record a in B) at time a in A using a 0.2 nA–40 ms pulse. Second, a cell was penetrated, as evidenced by negative deflection in DC tracing A to approximately −18 mV. This was followed by reassessing bridge balance at b in A. Resultant bridge imbalance of 24 mV is shown in record b in B and corresponds to an input resistance of 120 MΩ. Third, HRP was injected (dotted line in A) at a rate of 10 nA for 3 min, and when the DC potential returned to its full negative value, bridge balance was again reassessed (right-hand b in A). When the electrode was withdrawn slightly, DC potential returned to its interstitial value. Bridge balance was tested at time c in A and found (recording c in B) to be back in balance.