Human 5-HT3B -- Ser 276

Species Original Mutated to Mutation
Human Ser 276  

 

Rat Equivalent Asn 272    
Mouse Equivalent Asn 272

Thr

Ser

N272T

N272S

 

mAsn272Thr

Mouse 5-HT3B receptor subunit was expressed in HEK-293 cells with the 5-HT3A subunit.

Homomeric 5-HT3A receptors have a higher sensitivity to block by picrotoxin than do 5-HT3A/B receptors. This study examined the determinants of picrotoxin sensitivity in 5-HT3 receptors. The mouse 5-HT3B N272 residue is a determinant of picrotoxin inhibition. When replaced by the equivalent residue in the 5-HT3A subunit the 5-HT3B N272T mutant enhanced picrotoxin sensitivity of heteromeric 5-HT3A/B receptors. However, the mutant receptors were not as sensitive to picrotoxin as were homomeric 5-HT3A receptors, suggesting that other residues within the 5-HT3B subunit contribute to the reduced picrotoxin sensitivity of heteromeric receptors. 5-HT3 sensitivity of the mutant heteromeric receptor was increased slightly compared to the wild type heteromeric receptor.

When this mutant was combined with V273T there was no additional increase in 5-HT potency, nor was there an increase in picrotoxin sensitivity.

 

mAsn272Ser

The equivalent residue in the human 5-HT3B subunit is serine. The mouse 5-HT3B N272S mutation increased picrotoxin sensitivity, suggesting that this residue may contribute to a higher picrotoxin sensitivity in human heteromeric receptors.

 

Receptor (mouse) 5-HT EC50 (mM) PTX IC50 (mM)
5-HT3A Wild-Type 1.2 +/- 0.07 41.2 +/- 5.6
5-HT3A: S268A (S2'A) 1.0 +/- 0.03* 45.6 +/- 5.2
5-HT3A: T272F (T6'F) 0.9 +/- 0.09* 1900 +/- 300**
5-HT3A: L273T ( L 7'T) 2.0 +/- 0.05** 4.0 +/- 0.5**
5-HT3A/B Wild-Type 1.0 +/- 0.1 1135 +/- 131
5-HT3B: N272T (N6'T) 0.5 +/- 0.03** 213 +/- 24**
5-HT3B: N272S(N6'S) 0.4 +/- 0.01** 173 +/- 28**
5-HT3B: V273T (V7'T) 0.6 +/- 0.09** 866 +/- 35
5-HT3B: N272T, V273T (N6'T,V7'T) 0.4 +/- 0.01** 343 +/- 45**

*Significantly different from the wild-type receptor (p<0.05)

**Significantly different from the wild-type receptor (p<0.01)

***Significantly different from the wild-type 5-HT3A receptor

Das P, Dillion GH. (2005) Molecular determinants of picrotoxin inhibition of 5-hydroxytryptamine type 3 receptors. The Journal of pharmacology and experimental therapeutics 314(1):320-8

 

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