isotonic solutions

D.K. dk at
Wed Mar 27 00:09:27 EST 2002

wolfsc at ("Wolfgang Schechinger") wrote:
>Dear all, 
>isotonic NaCl of course is considered to be 0.9% m/v 
>thus (9g/l)/(58.44g/mol) = 154 mM.
>Since dissociation is close to 100% would ionic strength then be 308 mM ([Na+] 
>+ [Cl-]) = 2 * 154 mM or is it 154 mM by "definition"?

AFAIR, ionic strength is measured in ionic eq. and would be 1/2*(1+1)*M=0.154
Tonicity deals with osmolarity, for which physiological range is 300-350 mOsm.
>I'd lik to apply some buffered solutions on cells for maybe 1 hour. They have 
>be physiological in order to not damage them too much. 
>So, do I just add NaCl to achieve accurate ionic strength or do I need to 
>consider other ions for balance (KCl, others, which?)

"Normal" cells have very efficient ways of maintaning proper osmotic
balance and are not very sensitive to moderate variations in osmolarity. 
Any of a zillion different PBS or Ringer solution formulations would do. 
Simplest is 10 mM Pi, 150 mM NaCl (or 147 mM NaCl + 5 mM KCl), 
pH 7.2-7.4. Glucose at 5-20 mM, Ca2+ and/or Mg2+ at 2-5 mM are 
optional. One hour is not very long and in any case your cells will be 


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