I am looking for calculations to convert the concentration of crude compounds fed to animals (in mg/kg) to a physiological concentration (in M) for brain slices whole cell patch clamp experiments. Does anyone know how this calculation works?
Thank you.
This would be highly dependent on a number of factors e.g. bioavailability, first pass and second pass kinetics, how well the compound crosses the BBB, how well the compound partitions into lipids, protein binding, etc. Often times we look at one chemical who's pharmacological properties are already well defined. If you are trying to look into a novel chemical, you may need to perform a physiological test to determine how much of that substance is staying in the brain of an animal at a particular time point post-feeding. That being said I am afraid there is not a simple formula to determine how much X to place on an organotypic slice to mimic feeding a certain amount of X to an animal.
If there are a lot of number of compounds it its not so easy to convert into M, you need to determine the abundance of each compound in mixture and to make there relation (e.g. 1:10:20:5:2 - I hope you understand) and then to make the mixture of them. That is quite complicate as i can see from here.
If it's single compound then u need to see it's molecular weight and to see how many mg of that compound you have applied to animal (not mg/kg!). Calculate number of M in that amount of mg that are given to the animal (putting aside pharmacokinetics and pharmacodynamic). After that apply several concentrations of compound on your brain slices (e.g. 1M, 0.1M, 0.01M, 0.001M - or you can take bigger difference between concentrations)
Selected physical units:
'kg/kg' .. mass fraction of substance (mass of substance per mass of total mixture)
'kg' .. mass of substance
'mol' .. amount of substance (about 6x10^23 number of particles)
'mol/kg' .. molality (amount of substance per mass of solvent), sometimes used also as amount of substance per total mass of mixture (which is almost the same for low concentrations)
'mol/L' .. molar concentration (amount of substance per volume of solution)
'L' .. volume of solution
'kg/L' .. density (volumetric mass density of total mixture)
'kg/mol' .. molecular weight (molar mass) of substance (can be estimated from weights of elements of periodic table, from which the molecules of substance are composed )
'M' is typically 'mol/L' the molar concentration (amount of substance per liter of solution). However some papers give it another meaning, so I recommend to use full notation as 'mol/L' to avoid missunderstandings.
It is a good practice to use these units as variables in equations. For example:
.. [kg/kg] / .. [kg/mol] = .. [mol/kg]
.. [mol/kg] * .. [kg/L] = .. [mol/L]
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