AMPA Receptor: Difference between revisions

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At this concentration we are exposing film for 30 days.
At this concentration we are exposing film for 30 days.


;Protocol B -- 42 nM [3H]AMPA
;Protocol B -- 42 nM [3H]AMPA
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Thus, I conclude that protocol B would be optimal given we order 250 uCi and protocol A will remain optimal given we order 25 uCi of [3H]AMPA.
;Thus, I conclude that protocol B would be optimal given we order 250 uCi and protocol A will remain optimal given we order 25 uCi of [3H]AMPA.
 
 
 
 
 
 


===Experimental determination of  receptor-ligand binding affinity for [3H]AMPA===
10 nM [<sup>3</sup>H]AMPA bound 32% of receptors in rat. Frozen-thawed tissue in buffer with KCl bound 36% of receptors. Specific binding curve extrapolation estimates the Kd of AMPA to be ~28 nM ([http://www.sciencedirect.com/science/article/pii/0006899387900308 Olsen et al 1987]).




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| 3H-AMPA <br>15 nM || 50 mM Tris-HCl <br> 100 mM KCl <br> pH 7.4 <br> 10 min || 15 nM 3H-AMPA <br> Pre-Incubation Buffer <br> 60 min || Pre-Incubation Buffer <br> 10 min x2 baths <br> 1 dip diH2O
| 3H-AMPA <br>15 nM || 50 mM Tris-HCl <br> 100 mM KCl <br> pH 7.4 <br> 10 min || 15 nM 3H-AMPA <br> Pre-Incubation Buffer <br> 60 min || Pre-Incubation Buffer <br> 10 min x2 baths <br> 1 dip diH2O
|}
|}
===Experimental determination of  receptor-ligand binding affinity for [3H]AMPA===
10 nM [<sup>3</sup>H]AMPA bound 32% of receptors in rat. Frozen-thawed tissue in buffer with KCl bound 36% of receptors. Specific binding curve extrapolation estimates the Kd of AMPA to be ~28 nM ([http://www.sciencedirect.com/science/article/pii/0006899387900308 Olsen et al 1987]).
[[File:AMPAR.png]]

Revision as of 19:37, 12 April 2012

Determining ad hoc experimental parameters for quantitative autoradiography of AMPAR using [3H]AMPA ligand

Defining the parameters for a quantitative autoradiography experiment can be done three ways: (1) determined experimentally (not necessary for us), (2) taken from an existing protocol (which we did for our first experiment), (3) defined ad hoc using binding affinity data (which I've done below). After surveying the literature and consulting several databases, I've concluded that the binding affinity (dissociation constant Kd) for [3H]AMPA in rodents is ~28 nM. This means that a buffer containing a 28 nM concentration of [3H]AMPA will result in 50% of the total expressed AMPAR being bound to the radioligand. In the first experiment we used a 15 nM concentration; under the law of mass action this should result in 35% of expressed AMPAR being bound to ligand. The calculations for converting radioactivity (specific activity in Curies) to molecular concentrations is theoretically concrete, but converting this to film exposure days is only estimable.


The [3H]AMPA from Sigma is manufactured with the given parameters

  • Total Amount
- 25 uCi or 250 uCi
  • Specific Activity
- 60 Ci/mmol
  • Concentration
- 1 mCi/mL
  • Molecular Weight
- 186.2 g/mol

Radioactivity to Molecular Concentration 1 mCi/ml * 1 mmol/60 Ci * 1 Ci/1000 mCi = 1.67e-5 mmol/mL = 16.7 uM


Sigma sends us a 16.7 uM concentration of [3H]AMPA and we can order either 25 uL ($300) or 250 uL ($1100). We want to determine how many mice brains can be analyzed if we order 25 uL or 250 uL [3H]AMPA. When the tissue is cut using the cryostat it is placed on glass slides. The number of slides in the experiment is key. Using the drop technique (the best way to conserve our precious radioligand) each slide requires 1 mL of incubation buffer (e.g. the Tris buffer containing the [3H]AMPA). All the brain regions of interest can be fit onto 3 slides; therefore there are 3 slides per subject.

Now to compare protocols...


Protocol A -- 15 nM [3H]AMPA
  • 15 nM / (15 nM + 28 nM) = 35% bound receptors
  • 16.7 uM * x mL = .015 uM * 1 mL
  • x = 0.898 uL [3H]AMPA / mL Tris
  • 25 uL / 0.898 uL = 28 slides or 10 subjects
  • 250 uL / 0.898 uL = 278 slides or 92 subjects

At this concentration we are exposing film for 30 days.


Protocol B -- 42 nM [3H]AMPA
  • 42 nM / (42 nM + 28 nM) = 60% bound receptors
  • 16.7 uM * x mL = .042 uM * 1 mL
  • x = 2.5 uL [3H]AMPA / mL Tris
  • 25 uL / 2.5 uL = 10 slides or 3 subjects
  • 250 uL / 2.5 uL = 100 slides or 33 subjects

At this concentration we can estimate a film exposure time of ~21 days


Protocol C -- 100 nM [3H]AMPA
  • 100 nM / (100 nM + 28 nM) = 78% bound receptors
  • 16.7 uM * x mL = .1 uM * 1 mL
  • x = 6.0 uL [3H]AMPA / mL Tris
  • 25 uL / 6.0 uL = 4 slides or 1 subjects
  • 250 uL / 6.0 uL = 41 slides or 14 subjects

At this concentration we can estimate a film exposure time of ~16 days


Thus, I conclude that protocol B would be optimal given we order 250 uCi and protocol A will remain optimal given we order 25 uCi of [3H]AMPA.


Binding Assay 2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl) propionic acid (AMPA) receptors
PROCEDURES
Radioligand Pre-Incubation Incubation Wash
3H-AMPA
15 nM
50 mM Tris-HCl
100 mM KCl
pH 7.4
10 min
15 nM 3H-AMPA
Pre-Incubation Buffer
60 min
Pre-Incubation Buffer
10 min x2 baths
1 dip diH2O



Experimental determination of receptor-ligand binding affinity for [3H]AMPA

10 nM [3H]AMPA bound 32% of receptors in rat. Frozen-thawed tissue in buffer with KCl bound 36% of receptors. Specific binding curve extrapolation estimates the Kd of AMPA to be ~28 nM (Olsen et al 1987).