Epinephrine reversed high-concentration bupivacaine-induced inhibition of calcium channels and transient outward potassium current channels, but not on sodium channel in ventricular myocytes of rats

Abstract

Background: Epinephrine is a first-line drug for cardiopulmonary resuscitation, but its efficacy in the treatment of bupivacaine-induced cardiac toxicity is still in question. We hypothesized that epinephrine can reverse cardiac inhibition of bupivacaine by modulating ion flows through the ventricular myocyte membrane channels of rats. The aim of this study was to observe and report the effects of epinephrine on high-concentration bupivacaine-induced inhibition of sodium (INa), L-type calcium (ICa-L), and transient outward potassium (Ito) currents in the ventricular myocytes of rats.

Methods: The ventricular myocytes were isolated from Sprague-Dawley rats (250-300 g) by acute enzymatic dissociation. The whole-cell patch clamp technique was used to record the ion channel currents in single ventricular myocytes both before and after administration of medications.

Result: Administration of bupivacaine 100 μmol/L significantly reduced INa, (P < 0.05). However, administration of bupivacaine 100 μmol/L in conjunction with epinephrine 0.15 μg/ml had no effect in restoring INa to its previous state. Similarly, a sharp decline of ICa-L and Ito was observed after administration of bupivacaine 100 μmol/L (P < 0.05). In contrast to INa, ICa-L and Ito were significantly improved after the administration of the aforementioned combination of bupivacaine and epinephrine (P < 0.05).

Conclusion: Epinephrine can reverse high-concentration bupivacaine induced inhibition of ICa-L and Ito, but not INa. Thus, epinephrine's effectiveness in reversal of bupivacaine-induced cardiac toxicity secondary to sodium channel inhibition may be limited.

Figure 1

Representative I_Na traces obtained from ventricular myocytes groups: control, bupivacaine 100 μmol/L alone, and bupivacaine with epinephrine 0.15 μg/ml. Family of current traces obtained by applying a series of 50 ms pulses ranging from -90 mV to 50 mV with a holding potential of -90 mV.

Figure 2

The I_Na current-voltage relationship in the absence of bupivacaine, with bupivacaine 100 μmol/L alone, and bupivacaine 100 μmol/L in combination with epinephrine 0.15 μg/ml. Bupivacaine 100 μmol/L present in the perfusate contributed to an upper shift of the current density-voltage curve. Administration of 100 μmol/L bupivacaine and epinephrine 0.15 μg/ml did not effect any change in the curve.

Figure 3

Representative I_Ca traces obtained from ventricular myocytes groups: control, bupivacaine 100 μmol/L alone, and bupivacaine 100 μmol/L in combination with epinephrine 0.15 μg/ml. Family of current traces obtained by applying a series of 250 ms pulses ranging from -40 mV to 50 mV with a holding potential of -40 mV.

Figure 4

The I_Ca-L current-voltage relationship in the absence of bupivacaine, with bupivacaine 100 μmol/L alone, and bupivacaine 100 μmol/L in combination with epinephrine 0.15 μg/ml. Bupivacaine 100 μmol/L present in the perfusate contributed to an upper shift of the current density - voltage curve without changing the activation potential and the curve shape. However, bupivacaine 100 μmol/L in combination with epinephrine 0.15 μg/ml increased the I_Ca-L current and moved the curve of I_Ca-L downward.

Figure 5

Representative I_to traces obtained from ventricular myocyte groups: control, bupivacaine 100 μmol/L alone, and bupivacaine 100 μmol/L in combination with epinephrine 0.15 μg/ml. Family of current traces obtained by applying a series of 20ms test pulses of -40 mV to eliminate current through Na channels, which was then evoked by a series of 400 ms pulses ranging from -40 mV to 50 mV with a holding potential of -90 mV.

Figure 6

The I_to current-voltage relationship in the absence of bupivacaine, with 100 μmol/L bupivacaine alone, and 100 μmol/L bupivacaine in combination with epinephrine 0.15 μg/ml. Bupivacaine 100 μmol/L without epinephrine decreased I_to. On the other hand, I_to increased in response to the bupivacaine 100 μmol/L in combination with epinephrine 0.15 μg/ml.