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

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 (I_Na), L-type calcium (I_Ca-L), and transient outward potassium (I_to) 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 I_Na, (P < 0.05). However, administration of bupivacaine 100 μmol/L in conjunction with epinephrine 0.15 μg/ml had no effect in restoring I_Na to its previous state. Similarly, a sharp decline of I_Ca-L and I_to was observed after administration of bupivacaine 100 μmol/L (P < 0.05). In contrast to I_Na, I_Ca-L and I_to 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 I_Ca-L and I_to, but not I_Na. Thus, epinephrine’s effectiveness in reversal of bupivacaine-induced cardiac toxicity secondary to sodium channel inhibition may be limited.

The challenge to verify ceramide's role of apoptosis induction in human cardiomyocytes--a pilot study

Background

Cardioplegia and reperfusion of the myocardium may be associated with cardiomyocyte apoptosis and subsequent myocardial injury. In order to establish a pharmacological strategy for the prevention of these events, this study aimed to verify the reliability of our human cardiac model and to evaluate the pro-apoptotic properties of the sphingolipid second messenger ceramide and the anti-apoptotic properties of the acid sphingomyelinase inhibitor amitryptiline during simulated cardioplegia and reperfusion ex vivo.

Methods

Cardiac biopsies were retrieved from the right auricle of patients undergoing elective CABG before induction of cardiopulmonary bypass. Biopsies were exposed to ex vivo conditions of varying periods of cp/rep (30/10, 60/20, 120/40 min). Groups: I (untreated control, n = 10), II (treated control cp/rep, n = 10), III (cp/rep + ceramide, n = 10), IV (cp/rep + amitryptiline, n = 10) and V (cp/rep + ceramide + amitryptiline, n = 10). For detection of apoptosis anti-activated-caspase-3 and PARP-1 cleavage immunostaining were employed.

Results

In group I the percentage of apoptotic cardiomyocytes was significantly (p < 0.05) low if compared to group II revealing a time-dependent increase. In group III ceramid increased and in group IV amitryptiline inhibited apoptosis significantly (p < 0.05). In contrast in group V, under the influence of ceramide and amitryptiline the induction of apoptosis was partially suppressed.

Conclusion

Ceramid induces and amitryptiline suppresses apoptosis significantly in our ex vivo setting. This finding warrants further studies aiming to evaluate potential beneficial effects of selective inhibition of apoptosis inducing mediators on the suppression of ischemia/reperfusion injury in clinical settings.

The effect of levosimendan on bupivacaine-induced severe myocardial depression in anesthetized pigs

BACKGROUND AND OBJECTIVES

Levosimendan, an inodilator without proarrhythmogenic properties, has been shown to reverse ropivacaine-induced negative inotropy in isolated heart preparations. In this randomized and blinded study, we investigated whether levosimendan is able to reverse rapidly bupivacaine-induced myocardial depression in pigs.

METHODS

Twenty invasively monitored pigs anesthetized with isoflurane 1% received bupivacaine 2 mg/kg per minute into a central vein until mean arterial pressure decreased to 55% of baseline. Thereafter, levosimendan 80 microg/kg for 10 mins, followed by 0.7 microg/kg per minute during the next 50 mins (L-SIM) or corresponding amounts of placebo were administered intravenously. Simultaneously, Ringer's acetate was infused intravenously, 20 mL/kg for 10 mins, followed by 20 mL/kg for 50 mins.

RESULTS

Two pigs in each group developed cardiac arrest immediately after bupivacaine and could not be resuscitated. Bupivacaine induced widening of the QRS complex in the electrocardiogram and bradycardia.In the remaining 16 pigs, 3 (2 in L-SIM group and 1 in placebo group) needed short-lasting manual cardiac compression and 1 dose of epinephrine. Cardiac output, ejection fraction, and stroke power/end-diastolic volume recovered initially very rapidly in the L-SIM group.However, there was no time x group effect difference in the overall recovery in the various parameters between the 2 groups, except in heart rate which was higher (P G 0.05) when levosimendan was administered.During the 50-min levosimendan infusion, mean arterial pressure and systemic vascular resistance stayed slightly lower in comparison with placebo infusion, but the difference was not statistically significant.

CONCLUSIONS

Levosimendan together with the infusion of Ringer's solution rapidly reversed the cardiac depression, but there was no difference in overall cardiovascular recovery in comparison to treatment with Ringer's solution alone. Levosimendan-induced increase in heart rate possibly facilitated the recovery from bupivacaine intoxication.

Human cardiac tissue in a microperfusion chamber simulating extracorporeal circulation--ischemia and apoptosis studies

BACKGROUND

After coronary artery bypass grafting ischemia/reperfusion injury inducing cardiomyocyte apoptosis may occur. This surgery-related inflammatory reaction appears to be of extreme complexity with regard to its molecular, cellular and tissue mechanisms and many studies have been performed on animal models. However, finding retrieved from animal studies were only partially confirmed in humans. To investigate this phenomenon and to evaluate possible therapies in vitro, adequate human cardiomyocyte models are required. We established a tissue model of human cardiomyocytes preserving the complex tissue environment. To our knowledge human cardiac tissue has not been investigated in an experimental setup mimicking extracorporeal circulation just in accordance to clinical routine, yet.

METHODS

Cardiac biopsies were retrieved from the right auricle of patients undergoing elective coronary artery bypass grafting before cardiopulmonary bypass. The extracorporeal circulation was simulated by submitting the biopsies to varied conditions simulating cardioplegia (cp) and reperfusion (rep) in a microperfusion chamber. Cp/rep time sets were 20/7, 40/13 and 60/20 min. For analyses of the calcium homoeostasis the fluorescent calcium ion indicator FURA-2 and for apoptosis detection PARP-1 cleavage immunostaining were employed. Further the anti-apoptotic effect of carvedilol [10 microM] was investigated by adding into the perfusate.

RESULTS

Viable cardiomyocytes presented an intact calcium homoeostasis under physiologic conditions. Following cardioplegia and reperfusion a time-dependent elevation of cytosolic calcium as a sign of disarrangement of the calcium homoeostasis occurred. PARP-1 cleavage also showed a time-dependence whereas reperfusion had the highest impact on apoptosis. Cardioplegia and carvedilol could reduce apoptosis significantly, lowering it between 60-70% (p < 0.05).

CONCLUSIONS

Our human cardiac preparation served as a reliable cellular model tool to study apoptosis in vitro. Decisively cardiac tissue from the right auricle can be easily obtained at nearly every cardiac operation avoiding biopsying of the myocardium or even experiments on animals.The apoptotic damage induced by the ischemia/reperfusion stimulus could be significantly reduced by the cold crystalloid cardioplegia. The additional treatment of cardiomyocytes with a non-selective beta-blocker, carvedilol had even a significantly higher reduction of apoptotis.

The Effects of Levosimendan on Myocardial Function in Ropivacaine Toxicity in Isolated Guinea Pig Heart Preparations

BACKGROUND

Levosimendan is a novel drug used for inotropic support in heart failure, but its efficacy in local anesthetic-induced myocardial depression is not known. Therefore, we investigated the effects of levosimendan on the negative inotropic response to ropivacaine in isolated heart preparations of guinea pigs.

METHODS

Action potentials and force of contraction were studied with conventional techniques in guinea-pig papillary muscles. Heart rate, systolic pressure, the first derivative of left ventricular pressure (+dP/dt(max)), coronary flow, and PR and QRS intervals were measured in isolated constant-pressure perfused, nonrecirculating Langendorff heart preparations. Single or cumulatively increasing concentrations of levosimendan and ropivacaine were used either alone or in combination.

RESULTS

In isolated papillary muscle, ropivacaine reduced force of contraction in a concentration-dependent manner. Exposure to 10 microM levosimendan in the presence of 10 muM ropivacaine almost completely reversed the negative inotropic response. Sensitivity to the positive inotropic effect of levosimendan was not altered by 10 muM ropivacaine (-logEC50 [M] = 7.03 without versus 6.9 with ropivacaine, respectively). Action potential parameters were influenced only at the highest concentration. In the Langendorff heart, levosimendan significantly reversed the ropivacaine-induced reduction in heart rate, systolic pressure, coronary flow, and +dP/dt(max) to baseline values.

CONCLUSION

Levosimendan is an effective inotropic drug in ropivacaine-induced myocardial depression and levosimendan myocardial sensitivity, and efficacy was not affected by the local anesthetic. Our results suggest that the calcium-sensitizing action of levosimendan is effective in local anesthetic-induced cardiac depression.