The local anesthetic butamben inhibits total and L-type barium currents in PC12 cells.

BACKGROUND: Butamben or n-butyl-p-aminobenzoate is a long-acting experimental local anesthetic for the treatment of chronic pain when given as an epidural suspension. We have investigated whether Cav1.2/L-type calcium channels may be a target of this butamben action. METHODS: The effect of butamben on these channels was studied in undifferentiated rat PC12-cells with the whole-cell patch-clamp technique in voltage-clamp. Ba(2+) ions were used as the charge carriers in the calcium channel currents, whereas K(+) currents were removed using K(+) free solutions. RESULTS: Butamben 500 microM reversibly suppressed the total whole-cell barium current by 90% +/- 3% (n = 15), whereas 10 microM nifedipine suppressed this barium current by 75% +/- 7% (n = 6). Preexposure to butamben followed by washout decreased the inhibition by nifidepine to 47% +/- 5% (n = 10). These suppressive effects were not due to the measurement procedure and the drug vehicles in the solutions (<0.1% ethanol; n = 6). CONCLUSIONS: Butamben inhibits the total barium current through expressed calcium channel types in PC12 cells, including Cav1.2/L-type channels. Because Cav1.2 channels may also occur in human nociceptive C fibers, this result allows the possibility that these L-type channels are involved in the analgesic action of butamben.

The local anesthetic butamben inhibits and accelerates low-voltage activated T-type currents in small sensory neurons.

Butamben (BAB) is a local anesthetic that can be used in epidural suspensions for long-term selective suppression of dorsal root pain signal transmission and in ointments for the treatment of skin pain. Previously, high-voltage activated N-type calcium channel inhibition has been implicated in the analgesic effect of BAB. In the present study we show that low-voltage activated or T-type calcium channels may also contribute to this effect. Typical transient T-type barium currents, selectively evoked by low-voltage (-40 mV) clamp stimulation of small (approximately 20 microm diameter) dorsal root ganglion neurons from newborn mice, were inhibited by BAB with an IC50 value of approximately 200 microM. Furthermore, 200 microM BAB accelerated T-type current activation, deactivation, and inactivation kinetics, comparable to earlier observations for N-type calcium channels. Finally, 200 microM BAB had no effect on the midpoint potential and slope factor of the activation curve, although it caused a approximately 3 mV hyperpolarizing shift of the inactivation curve, without affecting the slope factor. We conclude that BAB inhibits T-type calcium channels with a mechanism associated with channel kinetics acceleration.

The block of total and N-type calcium conductance in mouse sensory neurons by the local anesthetic n-butyl-p-aminobenzoate.

To contribute to the understanding of the mechanism underlying selective analgesia by epidural application of suspensions of the local anesthetic butamben (n-butyl-p-aminobenzoate; BAB), we investigated the effect of dissolved BAB on calcium channels in sensory neurons. Small-diameter dorsal root ganglion neurons from newborn mice were used to measure whole-cell barium or calcium currents through calcium channels upon voltage-clamp stimulation. BAB suppressed the voltage-step-evoked barium current of these cells in a concentration-dependent manner with a 50% inhibitory concentration of 207 +/- 14 microM (n = 40). A similar concentration dependency was found for the pharmacologically isolated N-type component of the whole-cell barium current. The time constants of inactivation and deactivation of the N-type current became smaller in the presence of BAB, thus suggesting that kinetic changes are involved in the inhibition of this current. BAB caused a similar inhibition of the total calcium current and its N-type component when these currents were evoked by command potentials with the shape of an action potential. This inhibition of calcium currents by BAB should be considered in the search for the mechanism of selective analgesia by epidural suspensions of this local anesthetic.

Electrophysiology and morphometry of the Aalpha- and Abeta-fiber populations in the normal and regenerating rat sciatic nerve.

We studied electrophysiological and morphological properties of the Aalpha- and Abeta-fibers in the regenerating sciatic nerve to establish whether these fiber types regenerate in numerical proportion and whether and how the electrophysiological properties of these fiber types are adjusted during regeneration. Compound action potentials were evoked from isolated sciatic nerves 12 weeks after autografting. Nerve fibers were gradually recruited either by increasing the stimulus voltage from subthreshold to supramaximal levels or by increasing the interval between two supramaximal stimuli to obtain the cumulative distribution of the extracellular firing thresholds and refractory periods, respectively. Thus, the mean conduction velocity (MCV), the maximal charge displaced during the compound action potential (Q(max)), the mean firing threshold (V(50)), and the mean refractory period (t(50)) were determined. The number of myelinated nerve fibers and their fiber diameter frequency distributions were determined in the peroneal nerve. Mathematical modeling applied to fiber recruitment and diameter distributions allowed discrimination of the Aalpha- and Abeta-fiber populations. In regenerating nerves, the number of Aalpha-fibers increased fourfold while the number of Abeta-fibers did not change. In regenerating Aalpha- and Abeta-fibers, the fiber diameter decreased and V(50) and t(50) increased. The regenerating Aalpha-fibers' contribution to Q(max) decreased considerably while that of the Abeta-fibers remained the same. Correlation of the electrophysiological data to the morphological data provided indications that the ion channel composition of both the Aalpha- and Abeta-fibers are altered during regeneration. This demonstrates that combining morphometric and electrophysiological analysis provides better insight in the changes that occur during regeneration.