See: Inyushin et al, 2013, Elecrophysiological compartmentalization in perivascular astrocytes.
Abstract:Astrocytes have diverse functions in the brain that require heterogenic distribution of ion channels, transporters and other specific molecules in different cell compartments. It is known that astrocytes take up necessary substances from the blood stream using specialized transport molecules situated at their endfeet; where Kir4.1 potassium rectifier and aquaporin channels also are localized. That’s why we developed the approach to study astrocyte endfeet in brain slices electrophysiologycally. We found that astrocytes attached to blood vessels have elongated endfeet enwrapping blood vessel, suitable for patch-clamping with small-tip electrode. We used fluorescent injections and other imaging methods to confirm endfeet patch-clamping, and for comparison patched both endfeet of perivascular astrocytes on blood vessels as well as cell bodies of these astrocytes from rat hippocampal brain slices. The membrane potentials of different compartments after 5 minutes of dialysis with standard intracellular solution were different: -92 ± 2.1 mV in endfeet versus -85 ± 1.3 mV in soma. Barium-sensitive Kir currents recorded from endfeet of astrocytes were substantially larger than those recorded from astrocyte somata. We also studied signal propagation of de- and hyperpolarization from endfeet to the soma and back. We found that electrical signals are strongly reduced between these cell compartments regardless of the direction of signal propagation. We also have found that astrocyte endfeets are heavily interconnected by gap junctions.
Patch-clamping endfeet.
Electrode (with LY 1 mg/ml) pressed to the blood vessel thus became attached to the endfoot of astrocyte. A. Fluorescent image of the electrode and the attached astrocyte endfoot, the dye spreading from endfoot to the astrocyte process. B. The same picture using DIC optics. The blood vessel position shown by dash-line cylinder on both images.
While in (B) the access resistances were statistically similar in both compartments, the membrane potentials after 5 minutes of dialysis with standard intracellular solution were different: -92 ± 2.1 mV in endfeet versus -85 ± 1.3 mV in soma.