Macroscopic ionic currents within the human leg.

Recent research on developing and healing tissues suggests that small quasi-DC ionic currents (of magnitude 10-20 microA) may play a controlling role in the initiation and organisation of growing tissues, but the difficulties of measuring such small currents have led to confusing results. Sensitive magnetometry provides a method of demonstrating and, to some extent, locating such currents. A SQUID magnetometer system has been built and used to investigate the magnetic fields around the uninjured human leg. Analysis of the magnetic fields reveals the presence of slowly changing macroscopic current loops (of magnitude up to 12 microA) within the leg. These currents are broadly similar in all subjects, and show day-to-day reproducibility in individuals. They change predictably with time of muscle relaxation (over an hour), and revert to the original form on muscular exertion. These currents are of significance when considering the therapeutic use of injected current for the healing of non-union in bone.