S(+)-ketamine, but not R(-)-ketamine, reduces postischemic adherence of neutrophils in the coronary system of isolated guinea pig hearts

Ketamine attenuates the Na+-dependent Ca2+ overload in rabbit ventricular myocytes in vitro by inhibiting late Na+ and L-type Ca2+ currents

AIM

Intracellular Ca(2+) ([Ca(2+)]i) overload occurs in myocardial ischemia. An increase in the late sodium current (INaL) causes intracellular Na(+) overload and subsequently [Ca(2+)]i overload via the reverse-mode sodium-calcium exchanger (NCX). Thus, inhibition of INaL is a potential therapeutic target for cardiac diseases associated with [Ca(2+)]i overload. The aim of this study was to investigate the effects of ketamine on Na(+)-dependent Ca(2+) overload in ventricular myocytes in vitro.

METHODS

Ventricular myocytes were enzymatically isolated from hearts of rabbits. INaL, NCX current (INCX) and L-type Ca(2+) current (ICaL) were recorded using whole-cell patch-clamp technique. Myocyte shortening and [Ca(2+)]i transients were measured simultaneously using a video-based edge detection and dual excitation fluorescence photomultiplier system.

RESULTS

Ketamine (20, 40, 80 μmol/L) inhibited INaL in a concentration-dependent manner. In the presence of sea anemone toxin II (ATX, 30 nmol/L), INaL was augmented by more than 3-fold, while ketamine concentration-dependently suppressed the ATX-augmented INaL. Ketamine (40 μmol/L) also significantly suppressed hypoxia or H2O2-induced enhancement of INaL. Furthermore, ketamine concentration-dependently attenuated ATX-induced enhancement of reverse-mode INCX. In addition, ketamine (40 μmol/L) inhibited ICaL by 33.4%. In the presence of ATX (3 nmol/L), the rate and amplitude of cell shortening and relaxation, the diastolic [Ca(2+)]i, and the rate and amplitude of [Ca(2+)]i rise and decay were significantly increased, which were reverted to control levels by tetrodotoxin (TTX, 2 μmol/L) or by ketamine (40 μmol/L).

CONCLUSION

Ketamine protects isolated rabbit ventricular myocytes against [Ca(2+)]i overload by inhibiting INaL and ICaL.

Ketamine reduces inducible superoxide generation in human neutrophils in vitro by modulating the p38 mitogen-activated protein kinase (MAPK)-mediated pathway

Many cellular stresses and inflammatory stimuli can activate p38 mitogen-activated protein kinase (MAPK), a serine/threonine kinase in the MAPK family. The different stimuli act via different receptors or signalling pathways to induce phosphorylation of the cytosolic protein p47(phox), one subunit of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Formyl-methionyl-leucyl-phenylalanine (fMLP) has been shown to induce the p38 MAPK phosphorylation during the respiratory burst in human neutrophils. Here, we show that treatment with S(+)-ketamine or R(-)-ketamine at different concentrations (50, 100, 200, 400 microM) reduced fMLP-induced superoxide anion generation and p47(phox) phosphorylation in neutrophils in a concentration-dependent manner (y = -0.093x + 93.35 for S(+)-ketamine and y = -0.0982x + 95.603 for R(-)-ketamine, respectively). While treatment with 50 microM ketamine inhibited fMLP-induced superoxide generation by 10%, treatment with 400 microM S(+)-ketamine and R(-)-ketamine reduced fMLP-induced superoxide generation to 60.5 +/- 8.3% and 60.0 +/- 8.5%, respectively, compared with that in neutrophils treated with fMLP alone. Furthermore, treatment with ketamine down-regulated both fMLP-induced p47(phox) and isoproterenol-induced p38 MAPK phosphorylation and superoxide production. Interestingly, treatment with SB203580, the p38 MAPK inhibitor, also mitigated fMLP-induced superoxide anion generation and p38 MAPK and p47(phox) phosphorylation as well as apoptosis in a concentration-dependent fashion in neutrophils. Therefore, ketamine racemes inhibited fMLP-induced superoxide anion generation and p47(phox) phosphorylation by modulating fMLP-mediated p38 MAPK activation in neutrophils.

Anaesthetics and immune function

Surgical trauma and anaesthetics may cause immune suppression, predisposing patients to postoperative infections. Furthermore, stress such as surgery and pain per se is associated with immune suppression which, in animal models, leads to an increased susceptibility to infection and tumour spread. Thus, by modulating the neurohumoral stress response, anaesthesia may indirectly affect the immune system of surgical patients. In particular, regional anaesthesia attenuates this stress response and the associated effects on cellular and humoral immunity. Additionally, anaesthetics may directly affect the functions of immune-competent cells. However, the reported effects of commercial preparations of, for example, propofol, etomidate and midazolam are highly dependent on the applied solvent. Immunosuppressive effects may be particularly relevant in the intensive care unit when anaesthetics are used as long-term sedatives. There is a striking body of evidence that long-term exposure to certain sedatives is paralleled by infectious complications. On the other hand, anti-inflammatory effects of anaesthetics may be therapeutically beneficial in distinct situations such as those involving ischaemia/reperfusion injury or the systemic inflammatory response syndrome. Consequently, sedatives should be administered with careful regard to their respective potential immunomodulatory properties, the clinical situation, and the immunity status of the critically ill patient.

Ketamine: a new look at an old drug

Ketamine is a major drug for induction of patients with hypovolemia and for general anaesthesia under primitive conditions, but also has excellent properties for more generalized use in children, adults and other fragile patients. Potential beneficial effects on cardiac ischaemia and cerebral injury is presently explored, as well as the effects of ketamine as an potent analgesic drug. Combination with propofol or midazolam for sedation provides analgesia, sleep and spontaneous ventilation. The S-isomer of ketamine has a lower incidence of psychomimetic side effects in equianalgesic doses compared with the racemate or the R-isomer alone.