Molecular mechanisms underlying ketamine-mediated inhibition of sarcolemmal adenosine triphosphate-sensitive potassium channels

Ketamine plus Alcohol: What We Know and What We Can Expect about This

Drug abuse has become a public health concern. The misuse of ketamine, a psychedelic substance, has increased worldwide. In addition, the co-abuse with alcohol is frequently identified among misusers. Considering that ketamine and alcohol share several pharmacological targets, we hypothesize that the consumption of both psychoactive substances may synergically intensify the toxicological consequences, both under the effect of drugs available in body systems and during withdrawal. The aim of this review is to examine the toxicological mechanisms related to ketamine plus ethanol co-abuse, as well the consequences on cardiorespiratory, digestive, urinary, and central nervous systems. Furthermore, we provide a comprehensive discussion about the probable sites of shared molecular mechanisms that may elicit additional hazardous effects. Finally, we highlight the gaps of knowledge in this area, which deserves further research.

Cardiac Preconditioning Effect of Ketamine-Dexmedetomidine versus Fentanyl-Propofol during Arrested Heart Revascularization

Background

Myocardial damage due to ischemia and reperfusion is still unavoidable during coronary surgery. Anesthetic agents have myocardial preconditioning effect. Ketamine has sympathomimetic effect, while dexmedetomidine has a sympatholytic effect in addition to anesthetic, analgesic, and anti-inflammatory properties of both the drugs. This study was carried out to compare ketamine-dexmedetomidine (KD) combination with fentanyl-propofol (FP) combination on the release of cardiac troponin T (cTnT) and outcome after coronary artery bypass graft.

Patients and Methods

Ninety adult patients who underwent coronary artery bypass grafting (CABG) were assigned to receive either KD base anesthesia (KD group) or FP anesthesia (FP group). Trends of high-sensitive cTnT, CK-MB, and serum cortisol were followed in the first postoperative 24 h. Other outcomes were vital signs, weaning from cardiopulmonary bypass, tracheal extubation time, and echocardiographic findings.

Results

There was a significant lower release of cTnT in KD group than FP group during its peak values at 6 h after aortic unclamping (92.01 ± 7.332 in KD versus 96.73 ± 12.532 ng.L^-1 P = 0.032). significant lower levels of serum cortisol levels were noted KD group than in FP group at 6 and 12 h after aortic unclamping P < 0.001. As regard tracheal extubation time, patients assigned to KD group extubated earlier than whom in FP group 202.22 ± 28.674 versus 304.67 ± 40.598 min respectively P < 0.001.

Conclusion

The use of KD during on-pump CABG confers better myocardial protective and anti-inflammatory effect than fentanyl propofol.

A Non-Comparative Prospective Pilot Study of Ketamine for Sedation in Adult Septic Shock

Introduction

Sedation and analgesia in the intensive care unit (ICU) for patients with sepsis can be challenging. Opioids and benzodiazepines can lower blood pressure and decrease respiratory drive. Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist that provides both amnesia and analgesia without depressing respiratory drive or blood pressure. The purpose of this pilot study was to assess the effect of ketamine on the vasopressor requirement in adult patients with septic shock requiring mechanical ventilation.

Materials and Methods

We conducted a two-phase study in a multi-disciplinary adult ICU at a tertiary medical center. The first phase was a retrospective chart review of patients admitted with septic shock between July 2010 and July 2011; 29 patients were identified for a historical control group. The second phase was a prospective, non-randomized, open-label pilot study. Patients were eligible for inclusion if they were 18-89 yr of age with a diagnosis of septic shock, who also required mechanical ventilation for at least 24 h, concomitant sedation, and vasopressor therapy. Pregnant patients, patients in the peri-operative timeframe, and patients with acute coronary syndrome were excluded. Patients enrolled in the phase two pilot study received ketamine as the primary sedative. Ketamine was administered as a 1-2 mg/kg IV bolus, then as a continuous infusion starting at 5 mcg/kg/min, titrated 2 mcg/kg/min every 30 min as needed to obtain a Richmond Agitation Sedation Scale (RASS) goal of -1 to -2. If continuous sedation was still required after 48 h, patients were transitioned off ketamine and sedative strategy reverted to usual ICU sedation protocol. The primary outcome was the dose of vasopressor required at 24, 48, 72 and 96 h after enrollment. Secondary outcomes included cumulative ketamine dose, additional sedative and analgesics used, cumulative sedative and analgesic dosing at all time periods, corticosteroid use, days of mechanical ventilation, ICU LOS, hospital LOS, and mortality. Contiguous data were analyzed with unpaired t-tests and categorical data were analyzed with two-tailed, Fisher's exact test. This study was approved by our Institutional Review Board.

Results

From January 2012 to April 2015, a total of 17 patients were enrolled. Patient characteristics were similar in the control and study group. Ketamine was discontinued in one patient due to agitation at 36 h. There was a trend towards decreased norepinephrine and vasopressin use in the study group at all time periods. Regarding secondary outcomes, the study group received less additional analgesia with fentanyl at 24 and 48 h (p < 0.001), and less additional sedation with lorazepam, midazolam or dexmedetomidine at 24 h (p = 0.015).

Conclusion

This pilot study demonstrated a trend towards decreased vasopressor dose, and decreased benzodiazepine and opiate use when ketamine is used as the sole sedative. The limitations to our study include a small sample size and those inherent in using a retrospective control group. Our findings should be further explored in a large, randomized prospective study.

Anesthesia, microcirculation, and wound repair in aging

Age-related changes in skin contribute to impaired wound healing after surgical procedures. Changes in skin with age include decline in thickness and composition, a decrease in the number of most cell types, and diminished microcirculation. The microcirculation provides tissue perfusion, fluid homeostasis, and delivery of oxygen and other nutrients. It also controls temperature and the inflammatory response. Surgical incisions cause further disruption of the microvasculature of aged skin. Perioperative management can be modified to minimize insults to aged tissues. Judicious use of fluids, maintenance of normal body temperature, pain control, and increased tissue oxygen tension are examples of adjustable variables that support the microcirculation. Anesthetic agents influence the microcirculation of a combination of effects on cardiac output, arterial pressure, and local microvascular changes. The authors examined the role of anesthetic management in optimizing the microcirculation and potentially improving postoperative wound repair in older persons.

Inhibition of vascular adenosine triphosphate-sensitive potassium channels by sympathetic tone during sepsis

OBJECTIVE

Excessive opening of the adenosine triphosphate-sensitive potassium channel in vascular smooth muscle is implicated in the vasodilation and vascular hyporeactivity underlying septic shock. Therapeutic channel inhibition using sulfonylurea agents has proved disappointing, although agents acting on its pore appear more promising. We thus investigated the hemodynamic effects of adenosine triphosphate-sensitive potassium channel pore inhibition in awake, fluid-resuscitated septic rats, and the extent to which these responses are modulated by the high sympathetic tone present in sepsis. Temporal changes in ex-vivo channel activity and subunit gene expression were also investigated.

DESIGN

In vivo and ex vivo animal study.

SETTING

University research laboratory.

SUBJECTS

Male adult Wistar rats.

INTERVENTIONS AND MEASUREMENTS

Fecal peritonitis was induced in conscious, fluid-resuscitated rats. Pressor responses to norepinephrine and PNU-37883A (a vascular adenosine triphosphate-sensitive potassium channel inhibitor acting on the Kir6.1 pore-forming subunit) were measured at 6 or 24 hrs, in the absence or presence of the autonomic ganglion blocker, pentolinium. The aorta and mesenteric artery were examined ex vivo for rubidium efflux as a marker of adenosine triphosphate-sensitive potassium channel activity, and for adenosine triphosphate-sensitive potassium channel subunit gene expression using quantitative reverse transcription-polymerase chain reaction.

MAIN RESULTS

A total of 120 rats (50 sham-operated controls, 70 septic) were included. Septic rats became hypotensive after 12 hrs, with a 24-hr mortality of 51.7% (0% in controls). At 6 hrs, there was an attenuated pressor response to norepinephrine (p < .01) despite blood pressure being elevated (p < .01). PNU-37883A had no pressor effect, except in the presence of pentolinium (p < .01). Kir6.1 subunit mRNA increased significantly in the mesenteric artery while rubidium efflux was increased in both the aorta and mesenteric artery at 24 hrs.

CONCLUSIONS

Despite evidence of increased adenosine triphosphate-sensitive potassium channel activity in sepsis, it appears to be inhibited in vivo by high sympathetic tone. This may explain, at least in part, the reduced efficacy of adenosine triphosphate-sensitive potassium channel blockers in human septic shock.

Effects of aging on isoflurane-induced and protein kinase A-mediated activation of ATP-sensitive potassium channels in cultured rat aortic vascular smooth muscle cells

Isoflurane activates protein kinase A (PKA) in vascular smooth muscle cells (VSMCs), which in turn activates ATP-sensitive potassium (K(ATP)) channels and causes vasodilation. The present study was undertaken to examine whether advanced age influences the effect of isoflurane on K(ATP) channel activity in cultured VSMCs. We used VSMCs obtained from 12- to 15-week-old (adult) and 24- to 25-month-old (aged) male Wistar rats. Electrophysiological experiments were performed using cell-attached and inside-out patch-clamp techniques to monitor the K(ATP) channel activity. Application of isoflurane or forskolin to the bath solution in cell-attached recordings induced a significant increase in K(ATP) channel activity in the VSMCs from the adult group. However, K(ATP) channel opening induced by isoflurane, but not forskolin, was significantly suppressed by aging. On the other hand, cell-free recordings showed similar pharmacologic sensitivity to the K(ATP) channel opener pinacidil, inward rectification, and unitary conductance (40–45 pS) between groups. In addition, direct K(ATP) channel activation by c-PKA in the inside-out patches was similar in both groups. Furthermore, increasing PKA activation in cell-attached patches by CPT-cAMP restored isoflurane's effects in the aged group. These results suggest that aging decreases isoflurane-induced PKA activation, resulting in attenuation of K(ATP) channel opening.

Comparison of the Effects of Ketamine-Dexmedetomidine and Sevoflurane-Sufentanil Anesthesia on Cardiac Biomarkers After Cardiac Surgery: An Observational Study

Inhalational anesthetics have demonstrated cardioprotective effects against myocardial ischemia-reperfusion injury. Clinical studies in cardiac surgery have supported these findings, although not with the consistency demonstrated in experimental studies. Recent investigations have questioned the advantages of inhalational over intravenous anesthetics with respect to cardiac protection. Ketamine has been shown to be comparable with sufentanil, and has even demonstrated anti-inflammatory properties. Dexmedetomidine has been established as a sedative/anesthetic drug with analgesic properties, and has also demonstrated myocardial protective effects. In this retrospective observational study, the influence of ketamine-dexmedetomidine-based anesthesia (KET-DEX group; n=17) on the release of cardiac biomarkers was compared with that of sevoflurane-sufentanil-based anesthesia (SEVO group; n=21) in patients undergoing elective coronary artery bypass grafting. Compared with the SEVO group, the KET-DEX group exhibited significantly reduced cardiac troponin I (2.22±1.73 vs. 3.63±2.37 µg/l; P=0.02) and myocardial fraction of creatine kinase (CK-MB) levels (12.4±10.4 vs. 20.3±11.2 µg/l; P=0.01) on the morning of the first postoperative day. Furthermore, cardiac troponin I release, evaluated as the area under the curve, was significantly reduced in the KET-DEX group (32.1±20.1 vs. 50.6±23.2; P=0.01). These results demonstrate the cardioprotective effects of ketamine-dexmedetomidine anesthesia compared with those of sevoflurane-sufentanil anesthesia.

Dexmedetomidine directly inhibits vascular ATP-sensitive potassium channels

AIMS

Dexmedetomidine is reported to have an effect on peripheral vasoconstriction; however, the exact mechanisms underlying this process are unclear. In this study, we hypothesized that dexmedetomidine-induced inhibition of vascular ATP-sensitive K(+) (K(ATP)) channels may be associated with this vasoconstriction. To test this hypothesis, we investigated the effects of dexmedetomidine on vascular K(ATP)-channel activity at the single-channel level.

MAIN METHODS

We used cell-attached and inside-out patch-clamp configurations to examine the effects of dexmedetomidine on the activities of native rat vascular K(ATP) channels, recombinant K(ATP) channels with different combinations of various inwardly rectifying potassium channels (Kir6.0 family: Kir6.1, 6.2) and sulfonylurea receptor subunits (SUR1, 2A, 2B), and SUR-deficient channels derived from a truncated isoform of Kir6.2 subunit, namely, Kir6.2ΔC36 channels.

KEY FINDINGS

Dexmedetomidine was observed to inhibit the native rat vascular K(ATP) channels in both cell-attached and inside-out configurations. This drug also inhibited the activity of all types of recombinant SUR/Kir6.0 K(ATP) channels as well as Kir6.2ΔC36 channels with equivalent potency.

SIGNIFICANCE

These results indicate that dexmedetomidine directly inhibits K(ATP) channels through the Kir6.0 subunit.

Short-term effects of ketamine and isoflurane on left ventricular ejection fraction in an experimental Swine model

Background. General anesthesia is an essential element of experimental medical procedures. Ketamine and isoflurane are agents commonly used to induce and maintain anesthesia in animals. The cardiovascular effects of these anesthetic agents are diverse, and the response of global myocardial function is unknown. Methods. In a series of 15 swine, echocardiography measurements of left ventricular ejection fraction (LVEF) were obtained before the animals received anesthesia (baseline), after an intramuscular injection of ketamine (postketamine) and after inhaled isoflurane (postisoflurane). Results. The mean LVEF of an unanesthetized swine was 47 ± 3%. There was a significant decrease in the mean LVEF after administration of ketamine to 41 + 6.5% (P = 0.003). The addition of inhaled isoflurane did not result in further decrease in mean LVEF (mean LVEF 38 ± 7.2%, P = 0.22). Eight of the swine had an increase in their LVEF with sympathetic stimulation. Conclusions. In our experimental model the administration of ketamine was associated with decreased LV function. The decrease may be largely secondary to a blunting of sympathetic tone. The addition of isoflurane to ketamine did not significantly change LV function. A significant number of animals had returned to preanesthesia LV function with sympathetic stimulation.

Effects of ketamine on nicorandil induced ATP-sensitive potassium channel activity in cell line derived from rat aortic smooth muscle

PURPOSE

Nicorandil opens adenosine triphosphate-sensitive potassium (K(ATP)) channels in the cardiovascular system and is being increasingly used for the treatment of angina pectoris. In the present study, we tested whether intravenous anesthetic agent ketamine affected nicorandil-induced native vascular K(ATP) channel activation.

METHODS

We used excised inside-out patch clamp configurations to investigate the direct effects of ketamine racemate and S-(+)-ketamine on the activities of K(ATP) channels in cultured rat aortic smooth muscle cells. Furthermore, we also investigated whether intracellular MgADP could modulate ketamine inhibition.

RESULTS

Nicorandil significantly activated K(ATP) channel activity, whereas this channel activity was completely blocked by glibenclamide, a specific K(ATP) channel blocker. Ketamine racemate inhibited the nicorandil induced K(ATP) channel activity (IC(50)=34±1 µM, n=14), but S-(+)-ketamine was less potent than ketamine racemate in blocking nicorandil induced K(ATP) channel activities (IC(50)=226±7 µM, n=10). Application of MgADP to the intracellular side of the channel was able to decrease the inhibitory potency of ketamine racemate on nicorandil induced K(ATP) channel activities.

CONCLUSIONS

Our results indicate that ketamine inhibits nicorandil induced K(ATP) channel activities in a dose dependent and stereoselective manner. Furthermore, increase of intracellular MgADP attenuates the inhibitory potency of ketamine racemate. J. Med. Invest. 57: 237-244, August, 2010.

Differential effects of propofol and isoflurane on glucose utilization and insulin secretion

AIMS

Volatile anesthetics, such as isoflurane, reverse glucose-induced inhibition of pancreatic adenosine triphosphate-sensitive potassium (K(ATP)) channel activity, resulting in reduced insulin secretion and impaired glucose tolerance. No previous studies have investigated the effects of intravenous anesthetics, such as propofol, on pancreatic K(ATP) channels. We investigated the cellular mechanisms underlying the effects of isoflurane and propofol on pancreatic K(ATP) channels and insulin secretion.

MAIN METHODS

Intravenous glucose tolerance tests (IVGTT) were performed on male rabbits. Pancreatic islets were isolated from male rats and used for a perifusion study, measurement of intracellular ATP concentration ([ATP](i)), and patch clamp experiments.

KEY FINDINGS

Glucose stimulus significantly increased insulin secretion during propofol anesthesia, but not isoflurane anesthesia, in IVGTT study. In perifusion experiments, both islets exposed to propofol and control islets not exposed to anesthetic had a biphasic insulin secretory response to a high dose of glucose. However, isoflurane markedly inhibited glucose-induced insulin secretion. In a patch clamp study, the relationship between ATP concentration and channel activity could be fitted by the Hill equation with a half-maximal inhibition of 22.4, 15.8, and 218.8 μM in the absence of anesthetic, and with propofol, and isoflurane, respectively. [ATP](i) and single K(ATP) channel conductance did not differ in islets exposed to isoflurane or propofol.

SIGNIFICANCE

Our results indicate that isoflurane, but not propofol, decreases the ATP sensitivity of K(ATP) channels and impairs glucose-stimulated insulin release. These differential actions of isoflurane and propofol on ATP sensitivity may explain the differential effects of isoflurane and propofol on insulin release.

Mice are prone to kidney pathology after prolonged ketamine addiction

ICR mice were injected with ketamine for 1, 3 and 6 months and the kidneys and urinary bladders were excised and processed for histology. Starting from 1 month, all addicted mice showed invasion of mononuclear white cells, either surrounding the glomerulus or the other tubules in the kidney. The aggregation of these cells extended all the way to the pelvis and ureter. As well, in the urinary bladder, the epithelium became thin and there was submucosal infiltration of mononuclear inflammatory cells. Silver staining revealed a loss of nerve fibers amongst the muscles of the urinary bladder of the treated. Immunohistochemistry on choline acetyltransferase which is a marker for cholinergic neurons also demonstrated a decrease of those cells. We hypothesized that prolonged ketamine addiction resulted in the animals prone to urinary infection.

Effects of dopamine on ATP-sensitive potassium channels in porcine coronary artery smooth-muscle cells

BACKGROUND

Dopamine is reported to be a coronary vasodilator; however, the exact mechanism of dopamine action in the coronary circulation remains unclear. In this study, we hypothesized that dopamine-induced activation of coronary ATP-sensitive potassium (KATP) channels may be associated with coronary vasodilation. We therefore investigated the direct effects of dopamine on coronary KATP-channel activity.

METHODS

We used patch-clamp configurations to investigate the effects of dopamine on coronary KATP-channel activity.

RESULTS

Application of dopamine (10 to 10 M) to the bath solution during cell-attached recordings induced a concentration-dependent increase in KATP-channel activity. In contrast, dopamine failed to activate KATP channels in inside-out patches. Dopamine-induced coronary KATP-channel currents in cell-attached patches were inhibited by pretreatment with the selective D1-like antagonist, Sch-23390, but they were not influenced by the selective D2-like antagonist, domperidone, or the beta-adrenergic receptor antagonist, propranolol. The selective D1-like agonist, SKF-38393, and the adenylyl cyclase activator, forskolin, mimicked the dopamine effects on coronary KATP channels. Furthermore, pretreatment with an inhibitor of protein kinase A, Rp-cAMPS, abolished the dopamine-induced KATP-channel activation.

CONCLUSIONS

This study demonstrates that dopamine activates coronary KATP channels via signal transduction involving the D1-like dopaminergic receptor-protein kinase A-signaling pathway.

Hyperglycemia impairs isoflurane-induced adenosine triphosphate-sensitive potassium channel activation in vascular smooth muscle cells

BACKGROUND

Isoflurane activates vascular adenosine triphosphate sensitive potassium (K(ATP)) channels, and may induce vasodilation. In the present study, we investigated whether hyperglycemia modifies isoflurane activation of vascular K(ATP) channel.

METHODS

We used a cell-attached patch-clamp configuration to test the effects of isoflurane on K(ATP) channel activity in vascular smooth muscle cells (VSMCs) after incubation for 24 h in medium containing normal glucose (NG, 5.5 mM D-glucose), L-glucose (LG, 5.5 mM D-glucose plus 17.5 mM L-glucose), or high glucose (HG, 23 mM D-glucose). Superoxide levels in aortas were measured by the lucigenin-enhanced chemiluminescence technique.

RESULTS

Isoflurane-induced open probabilities were significantly reduced in VSMCs from arteries incubated in HG (0.06 +/- 0.01) compared with NG (0.17 +/- 0.02; P < 0.05) and LG (0.15 +/- 0.02; P < 0.05). Pretreatment of VSMCs with protein kinase C (PKC) inhibitors, calphostin C and PKC inhibitor 20-28, greatly reduced HG inhibition of isoflurane-induced K(ATP) channel activity. In addition, a PKC activator, PMA, mimicked the effects of HG. Superoxide release was significantly increased in arteries incubated in HG (18.3 +/- 11.5 relative light units (RLU) x s(-1) x mg(-1); P < 0.05 versus NG). Coincubated with polyethylene glycol-superoxide dismutase (250 U/mL), a cell-permeable superoxide scavenger, greatly reduced the HG-induced increase of superoxide, but failed to reduce HG inhibition of isoflurane-induced K(ATP) channel activity.

CONCLUSIONS

Our results suggest that the metabolic stress of hyperglycemia can impair isoflurane-induced vascular K(ATP) channel activity mediated by excessive activation of PKC. This could impede the coronary vasodilation response to isoflurane, causing ischemia or hypoxia in patients with perioperative hyperglycemia.

The effects of extracellular pH on vasopressin inhibition of ATP-sensitive K+ channels in vascular smooth muscle cells

BACKGROUND

Arginine vasopressin (AVP) inhibits ATP-sensitive potassium (K(ATP)) channels and may help to restore vascular tone in patients with vasodilatory shock. In the present study, we investigated whether extracellular acidification modifies the inhibition of vascular K(ATP) channels by AVP.

METHODS

We used a cell-attached patch-clamp configuration to investigate the effects of extracellular pH (pH(o)) on AVP-K(ATP) channel interaction in rat aortic smooth muscle cells.

RESULTS

Bath application of AVP significantly inhibited extracellular acidification (pH(o) = 6.5)-induced K(ATP) channel activity in a concentration-dependent manner, with an half-maximal inhibitory concentration (IC50) value of 16.8 pM. Furthermore, bath application of AVP significantly inhibited pinacidil-induced K(ATP) channel activity at mild (pH(o) = 7.0) and severe (pH(o) = 6.5) extracellular acidification, with IC50 values of 266.7 and 21.4 pM, respectively, but failed to significantly inhibit at normal pH (pH(o) = 7.4) or under alkalosis (pH(o) = 9.0). Augmentation of AVP inhibition of vascular K(ATP) channels during extracellular acidification was eliminated by pretreatment with OPC-21268, a specific blocker of the V1 receptor, but not by a V2 blocker, OPC-31260. AVP-induced inhibition was also suppressed by pretreatment with a protein kinase C inhibitor, calphostin C.

CONCLUSIONS

Our results suggest that AVP inhibits extracellular acidification-induced vascular K(ATP) channel activity, and that the inhibitory effects of AVP on vascular K(ATP) channels are enhanced by extracellular acidification via the V1 receptor-protein kinase C cell-signaling pathway. The potent inhibition of vascular K(ATP) channels by AVP under acidic conditions may make it suitable for management of vasodilatory shock.

Effects of intracellular MgADP and acidification on the inhibition of cardiac sarcolemmal ATP-sensitive potassium channels by propofol

PURPOSE

Propofol inhibits adenosine triphosphate-sensitive potassium (K(ATP)) channels, which may result in the blocking of ischemic preconditioning in the heart. During cardiac ischemia, sarcolemmal K(ATP) channel activity is regulated by the increased levels of cytosolic metabolites, such as adenosine diphosphate (ADP) and protons. However, it remains unclear whether these cytosolic metabolites modulate the inhibitory action of propofol. The aim of this study was to investigate the effects of intracellular MgADP and acidification on K(ATP) channel inhibition by propofol.

METHODS

We used inside-out patch-clamp configurations to investigate the effects of propofol on the activities of recombinant cardiac sarcolemmal K(ATP) channels, which are reassociated by expressed subunits, sulfonylurea receptor (SUR) 2A, and inwardly rectifying potassium channels (Kir6.2).

RESULTS

In the absence of MgADP, propofol inhibited the SUR2A/Kir6.2 channel currents in a concentration-dependent manner, and an IC(50) of 78 microM. Increasing the intracellular MgADP concentrations to 0.1 and 0.3 mM markedly attenuated the inhibitory potency of propofol, and shifted the IC(50) to 183 and 265 microM, respectively. Moreover, decreasing the intracellular pH from 7.4 to 6.5 attenuated the inhibitory potency of propofol, and shifted the IC(50) to 277 microM. In addition, propofol-induced inhibition of truncated Kir6.2DeltaC36 currents, which form a functional channel without SUR2A, was not affected by an increase in intracellular MgADP. However, intracellular acidification (pH 6.5) significantly reduced the propofol sensitivity of Kir6.2DeltaC36 channels.

CONCLUSION

Our results demonstrated that the existence of intracellular MgADP and protons attenuated the direct inhibitory potency of propofol on recombinant cardiac sarcolemmal K(ATP) channels, via SUR2A and Kir6.2 subunits, respectively.

[Role of ketamine in sepsis and systemic inflammatory response syndrome]

Ketamine is the only intravenous anesthetic that causes an increase in mean arterial pressure without compromising cardiac output. These beneficial effects are basically linked to stimulation of the sympathetic nervous system, inhibition of adenosine triphosphate-sensitive potassium channels and interactions with the nitric oxide pathway. Experimental and clinical studies have shown that ketamine exerts antiinflammatory properties by inhibiting the release of proinflammatory cytokines, such as tumor necrosis factor-alpha and interleukin-6. In addition, there is increasing evidence that early ketamine administration reduces mortality in experimental sepsis models. In view of the current literature ketamine appears to represent a beneficial therapeutic option for long-term sedation of patients with arterial hypotension resulting from sepsis and systemic inflammatory response syndrome (SIRS). However, it has to be taken into account that ketamine inhibits endothelial nitric oxide synthase, thereby potentially aggravating impaired (micro) regional blood flow in sepsis. Future studies are required to investigate the role of ketamine in the treatment of patients with sepsis and SIRS.

Augmented activity of adenosine triphosphate-sensitive K+ channels induced by droperidol in the rat aorta

Droperidol produces the inhibition of K+ channels in cardiac myocytes. However, the effects of droperidol on K+ channels have not been studied in blood vessels. Therefore, we designed the present study to determine whether droperidol modulates the activity of adenosine triphosphate (ATP)-sensitive K+ channels in vascular smooth muscle cells. Rat aortic rings without endothelium were suspended or used for isometric force and membrane potential recordings, respectively. Vasorelaxation and hyperpolarization induced by levcromakalim (10(-8) to 10(-5) M or 10(-5) M, respectively) were completely abolished by the ATP-sensitive K+ channel antagonist glibenclamide (10(-5) M). Droperidol (10(-7) M) and an alpha-adrenergic receptor antagonist phentolamine (3 x 10(-9) M) caused a similar vasodilator effect (approximately 20% of vasorelaxation compared with maximal vasorelaxation induced by papaverine [3 x 10(-4) M]), whereas glibenclamide did not alter vasorelaxation induced by droperidol. Droperidol (3 x 10(-8) M to 10(-7) M) augmented vasorelaxation and hyperpolarization produced by levcromakalim, whereas phentolamine (3 x 10(-9) M) did not alter this vasorelaxation. Glibenclamide (10(-5) M) abolished the vasodilating and hyperpolarizing effects of levcromakalim in the aorta treated with droperidol (10(-7) M). These results suggest that droperidol augments vasodilator activity via ATP-sensitive K+ channels. However, it is unlikely that this augmentation is mediated by the inhibition of alpha-adrenergic receptors in vascular smooth muscles.