Creatine binding in white muscle of the rainbow trout

The subcellular distribution of creatine (Cr) in white muscle of the rainbow trout (Oncorhynchus mykiss) was examined. Rainbow trout were cannulated via the dorsal injected with [amidino-14C] Cr. Following a 2 hour incubation period, fish were either sampled in the resting state (resting group) or exercised according to one of two different exercise protocols prior to sampling (buffering and depleting groups). The specific activity of phosphocreatine (SA[sub]PCr) was over three times the SA[sub]Cr within resting white muscle, and the SA[sub]PCr/SA[sub]Cr, ratio did not decrease towards 1 in muscle sampled from fish following either exercise protocol. This indicates; i) that a significant part of the pool of total Cr (the 'bound' pool) does not have access to creatine kinase (CK) in resting white muscle and ii) that this fraction of the Cr pool does not gain access to CK and become metabolically active during bouts of intense exercise. The SA[sub]PCr/SA[sub]Cr ratio increased significantly with decreasing Cr charge and thus the pool of Cr which was interacting with CK was not mixing homogeneously in all parts of the cell. This suggests limited subcellular mobility of PCr and Cr. The finding that a significant part of the pool of total Cr is not active in energy metabolism affects calculations of free adenosine diphosphate (ADP) through the CK equilibrium. Calculations of free ADP which take the limited access of Cr to CK into consideration imply a significant role for ADP as a regulator of metabolism.Science, Faculty ofZoology, Department ofGraduat