Mechanisms of action of pregabalin on cultured sensory neurones
In this study, the whole-cell patch clamp technique and fura-2 calcium (Ca2+) imaging techniques were employed to investigate and compare the effects of the novel antiepileptic/ antihyperalgesic drugs pregabalin and gabapentin. Investigations were done on cultured dorsal root ganglion neurones as they form a neuronal system that is a potential target for gabapentin/pregabalin pain control. The effects of pregabalin on the action potential properties of hyperexcitable multiple-firing cells were similar to those previously found for gabapentin. The changes on action potential properties suggested that pregabalin and gabapentin inhibition of repetitive firing of action potential spikes in DRG neurones is due to inhibition of Ca2+ dependent K+ currents as a result of Ca2+ current attenuation. Pregabalin and gabapentin inhibited voltage-activated Ca2+ currents to a similar maximal level and no additive inhibition was seen during simultaneous application of both drugs, suggesting a common site of action. The current inhibited was not conducted by L-type voltage-activated Ca2+ channels and was not due to a shift in the voltage dependence of activation. The continual presence of GABA or the GABAB receptor antagonist CGP52432 or intracellular photorelease of GTP-g-S had no effect on pregabalin-induced inhibition of Ca2+ currents. Inhibition of voltage-dependent Ca2+ current by pregabalin did not involve the actions a G-protein coupled receptor sensitive to the selective modulator SCH-202676 and unlike previous findings for gabapentin, pertussis toxin pre-treatment did not effect inhibition of Ca2+ currents. Ca2+-imaging techniques supported the magnitude of inhibition produced by pregabalin but also indicated the possibility of pregabalin having other actions that could produce an apparent increase in intracellular Ca2+ flux. This research indicates that pregabalin reduces excitatory properties of cultured DRG neurones by modulating both voltage-activated Ca2+ and K+ channels and its pharmacological activity is similar to that of gabapentin.