Abstract
An increase in fracture risk is well established in patients with epilepsy. However, the mechanism for this association is less well defined. Our aim was to isolate sodium channel currents in mouse primary calvarial osteoblasts using whole-cell patch-clamping and also to examine whether the anti-epileptic medication carbamazepine (CBZ) blocks these currents. Primary osteoblasts isolated from the calvariae of C57BL6 mice at postnatal day 2 (P2) were used to examine the impact of CBZ on sodium channel currents using automated whole-cell planar electrode voltage clamp recordings (Patchliner, Nanion, Germany). Currents were elicited from a holding potential of −80mV using a voltage protocol stepping from −100mV to +60mV in 10mV increments, for 20ms. CBZ (50μM) was applied to the cells in the continued presence of external tetraethylammonium (10mM) and internal Cs<sup>+</sup>. Following washout of CBZ, 10μM tetrodotoxin (TTX), a known voltage-gated sodium channel blocker, was applied. TTX sensitive (mean block of 89.96±2.14%; n=6; <i>p</i>< 0.0001) voltage-activated inward sodium currents were readily observed in P2 osteoblasts and bath application of CBZ (50μM) significantly inhibited these currents (mean block of 31.6±5.9%; n=7; <i>p</i><0.001). Mouse osteoblasts express native voltage-activated sodium channels, which are sensitive to CBZ and TTX. This novel demonstration of an inhibitory effect of CBZ on primary osteoblast sodium currents utilising Patchliner paves the way for semi-automated screening of anti-epileptic drugs, enabling further study to determine whether the effects on ion channel activity observed here translate to effects on signal transduction in osteoblasts, inhibition of osteoblast activity and clinically-relevant changes in bone quality.
Published Version
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