astrocytes

protein that gives astrocytes star-like shape

glial fibrillary acidic protein

astrocyte morphology (4)

• innumerable fine processes

• GFAP highly expressed → doesn’t exist in processes

• plasma membrane protein anchored green fluorescent (LCK-GFP) → enables visualization

• astrocytes don’t overlap w e/o

astrocytes form

gap junctions from cell to cell → have connect cytosols

excitability of an astrocyte (3)

• v. little when injected w current bc resting membrane potential ~85mV

• highly permeable to K+ → membrane potential close to K+ equilibrium potential

• v. leaky

astrocyte interaction w synapses (3)

• help support synaptic functioning

• make extensive contact w multiple dendrites/neurons

• 1 astrocyte can interact w 100,000 synapses

what are astrocytes doing in the brain (6)

• support + influence the synapse

• ionic homeostasis → ie. external K+ clearance

• feed synapses w glucose/lactate

• secrete growth factors for synaptogenesis

• neurotrans clearance + recycling

• modulate synaptic transmission

glutamate clearance via _______ generates an _______________

• excitatory amino acid transporters (EAAT1 + 2)

• inward Na+ current that can be recorded in voltage clamp

EAATs (4)

• use Na+ driving force to bring in glutamate

• 3 Na+ for 1 Glu- and 1 H+

• can work w/o ATP

• +2 ve

glutamine synthetase

converts glutamate into glutamine which is shuttled back into presynapse for reconversion + use in synaptic transmission

how can EAATs shape neuronal excitability

• ↑/↓ EAATs can produce longer lasting depolarization

Ca2+ signalling in astrocytes (3)

• poking astrocyte w pipette initiates wave of Ca2+ → propagates as a wave

• ATP/glutamate can start waves too

• intracellular propagation through IP3

what/how did paracrine ATP signalling show in astrocytes (3)

• gap jumping

• astrocytes releasing diffusible messenger (ATP)

• large gaps cannot be jumped → not enough ATP

Synaptically evoked astrocyte Ca2+ via metabotropic glutamate receptors (mGluR)

• strong synaptic activity ↑s astrocyte free intracellular Ca2+

• weak synaptic activity does not cause astrocyte signal

• needs lots of glutamate release to overcome uptake → spill out of the synapse + activate astrocyte mGluRs

bad experimental technique to stimulate astrocytes vs better technique

BAD

• injection of current → v. high current to ∆ MP of v. leaky astrocyte membrane

BETTER

• light-sensitive, caged Ca2+ molecules