Serial Dilutions : Now that you have those down, you need to prepare for lab. Du

Question

Serial Dilutions: Now that you have those down, you need to prepare for lab. During lab you will be asked to use eserine and atropine to modulate the dose---response curve for ACh. For these experiments you will need ONE specific concentration of eserine or atropine to use in conjunction with your known concentrations of ACh. So in this case, you are not creating a set of 10x dilutions, but rather diluting eserine and atropine so that they are a particular concentration in the tissue bath.

Below, you will find the stock concentrations of the reagents. Your task, is to devise a set of dilutions that will ultimately yield the correct final concentration in the bath. You can assume that you are using Tyrodes buffer to dilute the drugs.

REMEMBER: the total bath volume is 20 mLs and you want to achieve the desired bath concentration by injecting 200 L into the bath. FYI, the smallest volume you can accurately pipette in the lab is 10 L and you will be using 1.5mL tubes for mixing.

Eserine

Stock concentration: 1 mM (or 1 X 10---3 M)

Final bath concentration required: 1 X 10---6 M

Atropine

Stock concentration: 3 mM (or 3 X 10---3 M)

Final bath concentration required: 3 X 10---7 M

Write a brief description of how you will dilute the drugs so that you obtain the required final concentration.

Explanation / Answer

Eserine :

Using formula, M1V1 = M2V2

where,

M1 = stock concentration = 1 x 10^-3 M

V1 = unknown

M2 = final bath concentration = 1 x 10^-6 M

V2 = total bath volume = 20 mL

Feed values,

1 x 10^-3 x V1 = 1 x 10^-6 x 20

V1 = 0.02 mL = 20 microliter

So we would need to take 20 microliter of stock to prepare this solution.

Atropine :

Again using M1V1 = M2V2

where,

M1 = 3 x 10^-3 M

V1 = unknown

M2 = 3 x 10^-7 M

V2 = 20 mL

Feed values,

3 x 10^-3 x V1 = 3 x 10^-7 x 20

V1 = 0.002 mL = 2 microliter

To make it accurate, take 10 microliter of stock solution and dilute it with 90 microliter of water and make the volume upto 20 mL

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