Taurine is a very important organic osmolyte in most adult cells. Beca
use of this property it has been proposed that large changes in the in
tracellular content of taurine can osmotically stress the cell, causin
g changes in its size and shape. This hypothesis was examined by measu
ring cell dimensions of taurine deficient cardiomyocytes using confoca
l microscopy. Incubation of isolated neonatal rat myocytes with medium
containing 5 mM beta-alanine led to a 55% decrease in intracellular t
aurine content. Associated with the loss of taurine was a reduction in
cell size. Two factors contributed to the change in cell size. First,
there was a shift in cell shape, favoring the smaller of the two cell
ular configurations commonly found in the myocyte cell culture. Second
, the size of the polyhedral configuration was reduced after beta-alan
ine treatment. These same two events also contributed to size reductio
n in cardiomyocytes incubated with medium containing 30 mM mannitol. N
onetheless, some qualitative differences exist between cells osmotical
ly stressed by increasing the osmolality of the incubation medium and
decreasing intracellular osmolality. The results support a role for ta
urine in the regulation of osmotic balance in the neonatal cardiomyocy
te.