Low-temperature modification of the inhibitory effects of volatile anesthetics on airway smooth muscle contraction in dogs

Guideline-oriented perioperative management of patients with bronchial asthma and chronic obstructive pulmonary disease

Increased airway hyperresponsiveness is a major concern in the perioperative management of patients with bronchial asthma and chronic obstructive pulmonary disease. Guidelines using evidence-based medicine are continually being updated and published regarding the diagnosis, treatment, and prevention of these respiratory disorders. Perioperative management in these patients involves: (1) adequate control of airway hyperresponsiveness, including detection of purulent sputum and infection before surgery; (2) evidence-based control of anesthesia; and (3) the aggressive use of beta-2 adrenergic stimulants and the systemic administration of steroids for the treatment of acute attacks. Good preoperative control, including the use of leukotriene antagonists, can reduce the incidence of life-threatening perioperative complications. Awareness of recent guidelines is thus important in the management of patients with airway hyperresponsiveness. This review covers the most recent guidelines for the perioperative management of patients with bronchial asthma and chronic obstructive pulmonary disease.

Inhibitory effects of volatile anesthetics on currents produced on heterologous expression of KvLQT1 and minK in Xenopus oocytes

The slowly activating component of delayed rectifier K+ current (IKs) in the heart modulates the repolarization of cardiac action potential. We investigated the effects of the volatile anesthetics isoflurane and sevoflurane on cloned IKs coexpressed by KvLQT1 and minK. Currents were induced following injection into oocytes of KvLQT1 mRNA (10 ng) with or without minK mRNA (1 ng), which were transcribed in vitro from cDNAs of normal rats hearts. A two-electrode voltage-clamp recording technique was used to investigate the effects of isoflurane (0-1.5 minimum alveolar concentration, MAC) and sevoflurane (0-1.5 MAC) on IKs (KvLQT1 with minK) and KvLQT1 alone currents. Currents were activated by step depolarizations to a series of potentials from a holding potential of -80 mV and measured as the deactivating tail current on repolarization to -60 mV. Following a 2-s depolarization to 40 mV, isoflurane and sevoflurane caused potency-dependent reductions in IKs and KvLQT1 currents. Both of the volatile anesthetics tested accelerated the deactivation of IKs and KvLQT1 currents. We conclude that the significant inhibitory effect of volatile anesthetics on the cloned IKs may partly contribute to the clinical observations of the prolongation of the ventricular repolarization (Q-T interval) by the anesthetics.

Sevoflurane inhibits contraction of uterine smooth muscle from pregnant rats similarly to halothane and isoflurane

PURPOSE

The present study was designed to clarify the direct effects of the volatile anesthetics halothane, isoflurane and sevoflurane on oxytocin-induced uterine smooth muscle contraction from pregnant rats.

METHODS

Longitudinal smooth muscle layers were obtained from pregnant rats. Intracellular concentration of free Ca++ ([Ca++](i)) was measured, using a fluorescence technique, simultaneously with muscle tension. Inward Ba++ current (I(Ba)) through voltage-dependent Ca++ channels (VDCCs) was measured using a whole cell patch clamp technique. After incubation with 20 nM oxytocin, halothane, isoflurane or sevoflurane (1, 2, and 3%) was introduced into the tissue bath.

RESULTS

All volatile anesthetics significantly inhibited muscle contraction concomitant with a decrease in [Ca++](i). Volatile anesthetics also inhibited the peak I(Ba). When the anesthetic concentrations were expressed as multiples of minimum alveolar concentrations, there were no differences in the inhibitory potencies of the three volatile agents tested for muscle tension and VDCC.

CONCLUSIONS

Volatile anesthetics halothane, isoflurane and sevoflurane reduce the oxytocin-induced contraction of pregnant uterine smooth muscle. Inhibition of the contraction by the volatile anesthetics is due, at least in part, to the decrease in [Ca++](i), and the decrease in [Ca++](i) may be mediated by inhibition of VDCC activity.

The repolarizing effects of volatile anesthetics on porcine tracheal and bronchial smooth muscle cells

This study was conducted to determine the effects of volatile anesthetics (potent bronchodilators) on membrane potentials in porcine tracheal and bronchial smooth muscle cells. We used a current-clamp technique to examine the effects of the volatile anesthetics isoflurane (1.5 minimum alveolar anesthetic concentration [MAC]) and sevoflurane (1.5 MAC) on membrane potentials of porcine tracheal and bronchial (third- to fifth-generation) smooth muscle cells depolarized by a muscarinic agonist, carbachol (1 microM). The effects of volatile anesthetics on muscarinic receptor binding affinity were also investigated by using a radiolabeled receptor assay technique. The volatile anesthetics isoflurane and sevoflurane induced significant repolarization of the depolarized cell membranes in the trachea (from -19.8 to -23.6 mV and to -24.8 mV, respectively) and bronchus (from -24.7 to -29.3 mV and -30.4 mV, respectively) without affecting carbachol binding affinity to the muscarinic receptor. The repolarizing effect was abolished by a Ca(2+)-activated Cl(-) channel blocker, niflumic acid. These results indicate that volatile anesthetic-induced repolarization of airway smooth muscle cell membranes might be caused by a change in Ca(2+)-activated Cl(-) channel activity and that the different repolarized effects of the volatile anesthetics could in part contribute to the different effects of volatile anesthetics on tracheal and bronchial smooth muscle contractions.

IMPLICATIONS

By use of a current-clamp technique, the volatile anesthetics isoflurane and sevoflurane repolarized porcine airway smooth muscle cell membranes depolarized by a muscarinic agonist. This effect might be caused mainly by change in Ca(2+)-activated Cl(-) channel activity, not in K(+) channel activity.