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Protein kinase C (PKC)-dependent signaling pathways may be involved in the "memory" effect of anesthetic and ischemic preconditioning, which facilitates activation of cardioprotective adenosine triphosphate (ATP)-sensitive potassium channels during later ischemic challenge and ATP depletion. Using patch-clamp techniques, we found that exposure of isolated guinea pig cardiomyocytes to 1 mM of isoflurane after phorbol ester stimulation of PKC facilitates the induction of larger (P < or = 0.05) sarcolemmal K(ATP) channel currents (IKATP) during cell dialysis with 0.5, compared to 1.0, mM of ATP in the pipette (10 +/- 5 versus 2 +/- 1 pA/pF in five and six cells, respectively). A PKC inhibitor, bisindolylmaleimide, abolished the induction of IKATP by a second brief isoflurane exposure under these conditions. A diacylglycerol PKC activator applied via the pipette elicited concentration-related activation of IKATP. The diacylglycerol alone (0.5 microM) elicited I(KATP), averaging 5 +/- 3 pA/pF in nine cells. Briefly treating myocytes on the microscope stage with isoflurane, followed by washout and patching with the same diacylglycerol solution, elicited larger (P < or = 0.01) IKATP, averaging 40 +/- 9 pA/pF (10 cells), with an onset 48 +/- 2 min after anesthetic pretreatment. Facilitation of IKATP by isoflurane during the reduction of intracellular ATP is dependent on PKC, whereas "preconditioning" myocytes with isoflurane causes persistent changes in sarcolemmal KATP channel function, which enhance the induction of IKATP by a diacylglycerol.

Background: Cardioprotection by volatile anesthetic-induced preconditioning is known to involve intracellular signaling pathways. Recent studies have shown that protein kinase C (PKC) plays an important role in anesthetic-induced preconditioning. In this study, the effects of the activation of specific isozymes of PKC, specifically PKC-epsilon and -delta, on the modulation of the sarcolemmal adenosine triphosphate-sensitive potassium (sarcKATP) channel by isoflurane were investigated., Methods: The sarcKATP current was measured in ventricular myocytes isolated from guinea pig hearts using the whole cell configuration of the patch clamp technique. Peptides that induced the translocation of specific PKC isozymes were used to activate PKC-epsilon and PKC-delta., Results: Under whole cell conditions, isoflurane alone was unable to elicit the opening of the sarcKATP channel. Pretreatment with the specific PKC-epsilon activator, PP106, primed the sarcKATP channel to open in the presence of isoflurane. The resulting sarcKATP current densities in the presence of 0.88 mm isoflurane were 6.5 +/- 6.0 pA/pF (n = 7) and 40.4 +/- 18.2 pA/pF (n = 7) after pretreatment with 100 and 200 nm PP106, respectively. The PKC-epsilon antagonist PP93 abolished this effect. A scrambled peptide of the PKC-epsilon activator PP105 did not prime the sarcKATP channel. The PKC-delta activator PP114 was significantly less effective in priming the sarcKATP channel. 5-Hydroxydecanoate significantly attenuated the effect of the PKC-epdsilon activator on the sarcKATP channel. In addition, immunohistochemical analysis showed that the PKC-epsilon isoform translocated to both the mitochondria and sarcolemma after anesthetic-induced preconditioning, whereas the PKC-delta isoform translocated to the mitochondria., Conclusion: The PKC-epsilon isozyme primed the sarcKATP channel to open in the presence of isoflurane. The PKC-delta isozyme was significantly less effective in modulating the isoflurane effect on this channel.

Background: Halothane is known to potentiate catecholamine-induced depression of conduction velocity in Purkinje fibers but not endocardial muscle fibers. The purpose of this study was to examine the interactions of halothane with epinephrine and isoproterenol on canine epicardial conduction velocity at moderately elevated extracellular potassium concentration ([K]0)., Methods: Epicardial muscle strips (10x10x2 mm) were superfused with Tyrode's solution containing 4 or 8 mM [K]0 in the presence of 5 microM epinephrine or 1 microM isoproterenol with or without 0.8 mM halothane. Conduction velocity in the longitudinal and transverse directions relative to epicardial fiber orientation was recorded during alternate stimulation in each direction., Results: In the presence of halothane, a change from 4 to 8 mM [K]0 decreased (P< or =0.05) longitudinal and transverse conduction velocities by 26% and 21%, respectively. Isoproterenol alone at 4 and 8 mM [K]0 depressed (P<0.05) both longitudinal and transverse conduction velocities. However, the depression of longitudinal conduction velocity by isoproterenol at 4 mM [K]0 was attenuated by halothane. Epinephrine with or without halothane depressed (P<0.05) both longitudinal and transverse conduction velocities at 8 but not at 4 mM [K]0., Conclusion: The results do not support a synergistic interaction between halothane and epinephrine on myocardial conduction but do demonstrate depression of conduction by epinephrine at 8 mM [K+]0, a potassium ion concentration comparable to those reported following epinephrine infusions.

Background: Alpha1-adrenoceptor stimulation is known to produce electrophysiologic changes in cardiac tissues, which may involve modulations of the fast inward Na+ current (I(Na)). A direct prodysrhythmic alpha1-mediated interaction between catecholamines and halothane has been demonstrated, supporting the hypothesis that generation of halothane-epinephrine dysrhythmias may involve slowed conduction, leading to reentry. In this study, we examined the effects of a selective alpha1-adrenergic receptor agonist, methoxamine, on cardiac I(Na) in the absence and presence of equianesthetic concentrations of halothane and isoflurane in single ventricular myocytes from adult guinea pig hearts., Methods: I(Na) was recorded using the standard whole-cell configuration of the patch-clamp technique. Voltage clamp protocols initiated from two different holding potentials (V(H)) were applied to examine state-dependent effects of methoxamine in the presence of anesthetics. Steady state activation and inactivation and recovery from inactivation were characterized using standard protocols., Results: Methoxamine decreased I(Na) in a concentration- and voltage-dependent manner, being more potent at the depolarized V(H). Halothane and isoflurane interacted synergistically with methoxamine to suppress I(Na) near the physiologic cardiac resting potential of -80 mV. The effect of methoxamine with anesthetics appeared to be additive when using a V(H) of -110 mV, a potential where no Na+ channels are in the inactivated state. Methoxamine in the absence and presence of anesthetics significantly shifted the half maximal inactivation voltage in the hyperpolarizing direction but had no effect on steady-state activation., Conclusion: The present results show that methoxamine (alpha1-adrenergic stimulation) decreases cardiac Na+ current in a concentration- and voltage-dependent manner. Further, a form of synergistic interaction between methoxamine and inhalational anesthetics, halothane and isoflurane, was observed. This interaction appears to depend on the fraction of Na+ channels in the inactivated state. (Key words: Anesthetics, volatile: halothane; isoflurane; methoxamine. Patch clamp: whole-cell configuration; sodium current; ventricular guinea pig myocytes.)

Cardiac dysrhythmias during inhaled anesthesia are well documented and may, in part, involve depression of the fast inward Na+ current (INa) during the action potential upstroke. In this study, we examined the effects of halothane, isoflurane, and sevoflurane at clinically relevant concentrations on INa in single ventricular myocytes isolated enzymatically from adult guinea pig hearts. INa was recorded using standard whole-cell configuration of the patch clamp technique. Halothane at 0.6 mM and 1.2 mM produced significant (P < 0.05) depressions of peak INa of 12.3% +/- 1.8% and 24.4% +/- 4.1% (mean +/- SEM, n = 12), respectively. Isoflurane (0.5 mM, n = 12; 1.0 mM, n = 15) and sevoflurane (0.6 mM, n = 14; 1.2 mM, n = 12) were less potent than halothane, decreasing peak INa by 4.8% +/- 1.1% and 11.4% +/- 1.4% (isoflurane) and 3.0% +/- 0.7% and 10.7% +/- 3.9% (sevoflurane). The depressant effects on INa were reversible in all cases. For all anesthetics tested, the degree of block increased at more depolarizing potentials. Anesthetics induced significant shifts in the steady-state inactivation and activation of the channel toward more hyperpolarizing potentials. The present findings indicate that volatile anesthetics at clinical concentrations decrease the cardiac INa in a dose- and voltage-dependent manner. At approximately equianesthetic concentrations, the decrease of INa caused by halothane was twice that observed with isoflurane or sevoflurane.