Creatine Transport into Muscle Cells from the Blood Stream
(bringing it all together)
Legend: Creatine harnesses the potential energy of sodium (Na) wanting to enter the muscle cell. Therefore, any agent that increases the extrusion of sodium, should likewise increase the transport of creatine into the muscle cell. Physiological agensts that are well known to increase sodium efflux include insulin and adrenalin (epinephrine). Review Chapter 4 of my creatine guide for a more detailed discussion about the implications of this process to the athlete.
Two sodiums need to accompany each creatine molecule being transported inward. Therefore, doubling the driving force for sodium inwardly will effectively increase creatine transport by 50%.
Creatine transporter expression is also greatest on type II muscle fibers. Recall that these are the muscle fibers with the greatest requirement for creatine.
Finally, due to its electrical charge creatine becomes trapped within the muscle cell once transported within. PCr is even more highly charged and likewise is trapped once produced. Creatinine, on the other hand, lacks electrical charges at physiological pH and hence is able to escape across the muscle cell membrane. This is shown in greater detail here and establishes our daily creatine requirement.