Effects of Bupivacaine and Ropivacaine on High-voltage-activated Calcium Currents of the Dorsal Horn Neurons in Newborn Rats

Background: Local anesthetics, such as bupivacaine, have been reported to block calcium currents in primary sensory neurons and to interfere with the release of neurotransmitters in central nervous system neurons. However, it is unknown whether local anesthetics affect the calcium current activity of central nervous system neurons.

Methods: Using a traditional whole cell voltage clamp technique, effects of bupivacaine and ropivacaine on high-voltage-activated calcium currents (HVA-Ica) were investigated in enzymatically dissociated dorsal horn neurons of neonatal rats. Calcium currents were evoked by testing pulses from a holding potential of -90 to 0 mV.

Results: Bupivacaine significantly reduced HVA-Ica in a dose-dependent manner. The peak HVA-Ica decreased by 24.5 +/- 2.5, 32.0 +/- 6.8, 59.4 +/- 6.2, 88.3 +/- 1.5, and 91.6 +/- 1.1% in response to 10, 30, 50, 100 and 200 mu]m bupivacaine, respectively. Unlike bupivacaine, ropivacaine markedly increased HVA-Ica at lower concentrations (< 50 mu]m) but decreased HVA-Ica at higher concentrations (>= 50 mu]m). The percent increases in peak HVA-Ica induced by 10 and 30 mu]m ropivacaine were 95 +/- 19.1 and 41.6 +/- 8.3%, respectively. The percent decreases in response to 50, 100, and 200 mu]m ropivacaine were 21.1 +/- 2.1, 63.2 +/- 6.0 and 79.1 +/- 7.6%, respectively. Results indicate that the inhibitory potency of ropivacaine on HVA-Ica was significantly lower than that of bupivacaine at the same concentrations.