A reference curve for axial bioelectric potentials in rabbit tibia

Bicarbonate dependence of ion current in damaged bone

The aim of this work was to characterize the ion current that enters mouse metatarsal bones following damage to the cortex. We assessed both the spatial distribution of this current and its dependence on the presence of bicarbonate in the medium. We used a voltage-sensitive probe system vibrating in two dimensions and recorded the signal as function of the position of the probe with respect to the site of damage and of ion substitutions in the medium. When the cortex was damaged (50 microm cylindrical hole penetrating into the marrow cavity), we recorded a steady state net inward electrical current directed toward the site of damage. In nonbicarbonate media, the density of the current was maximal near the center of the hole and ranged from 6 to 18 microA/cm2. As the probe was moved off the center of the hole, measured current density decreased in a manner consistent with the hypothesis that the source of the inward current is localized to the hole. After changing bicarbonate concentration in the medium from 0 to 42 mM, the current density nearly doubled, then decayed back to its original level exponentially over 35 minutes. When the diaphysis of living bone was left intact the current density was close to background level either in the presence or absence of bicarbonate in the medium. Damaged dead bone did not drive any current higher than background level. We conclude that the vibrating probe technique is a powerful tool to characterize ion currents in injured bone, helping to understand the physiology of bone-plasma interface and the bone healing processes. The current density transiently doubled upon addition of bicarbonate, indicating that this ion may carry the electrical current in damaged bone, probably by pump-leak mechanisms operating at the bone-plasma interface.

Changes in bioelectric potentials on bone associated with direct current stimulation of osteogenesis

This study was designed to determine whether changes occur in the bioelectric potentials on bone during and after bone stimulation with a 20-microA direct current (DC) and whether the variations in bioelectric potentials are related to the variations in bone formation. The bioelectric potentials were recorded at different times on the rabbit distal tibial surface, during (current-on state) and after (current-off state) DC stimulation with a cathode implanted within the medullary canal. The new bone formed at the end of the experiment was quantitated and related to the bioelectric potentials recorded at current-on and current-off states, respectively. Direct current stimulation resulted in electronegative potential spike centered on the cathode tip while current was applied. After electrical stimulation was turned off, the residual potentials at the end of the experiment did not significantly differ from the initial values. Conversely, the time sequence of the changes was significantly different from the control to the experimental group. The variations in the induced potentials at current-on state were significantly related to the variations in bone formation. This study suggests the existence of a relationship among bioelectric potentials, DC stimulation, and osteogenesis.