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OBSTETRIC ANESTHESIA

The Role of K⁺ Channels on the Inhibitor Effect of Sevoflurane in Pregnant Rat Myometrium

Haluk Kafali, MD^*, Tijen Kaya, PhD, Sinan Gürsoy, MD^*, Ihsan Bagcivan, MD, Baris Karadas, MD, and Yusuf Sarioglu, PhD

Departments of *Anesthesiology and Pharmacology, Cumhuriyet University School of Medicine, Sivas, Turkey

Address correspondence and reprint requests to Dr. Haluk Kafali, Department of Anesthesiology, Cumhuriyet University School of Medicine, 58140 Sivas, Turkey. Address e-mail to haluk.kafali{at}isnet.net.tr

Volatile anesthetics and K⁺ channel openers inhibit spontaneous contractions in myometrial smooth muscle. Volatile anesthetics modulate K⁺ channel activity. We investigated the role of two K⁺ channel blockers on the effect of sevoflurane in pregnant rat myometrium. Term pregnant rat uteri were excised, and cross-sectional myometrial strips were mounted for isometric force recording. Sevoflurane inhibited the amplitude and frequency of spontaneous myometrial contractions in a concentration-dependent manner. The maximal inhibition measured in amplitude and frequency of spontaneous myometrial contractions with sevoflurane (at 3 minimum alveolar anesthetic concentration) was 44.32% and 33.32% of control contractions, respectively. Tetraethylammonium (TEA) and glibenclamide, K⁺ channel blockers, increased spontaneous myometrial contractions in a concentration-dependent manner. Sevoflurane responses were repeated at concentrations with no effect on spontaneous contractility of TEA, a Ca²⁺-activated K⁺ channel blocker, and glibenclamide, an adenosine triphosphate-sensitive K⁺ channel blocker, in myometrial strips. TEA (3.10^-4 M) caused a significant reduction in sevoflurane-induced inhibitor responses, but glibenclamide (10^-6 M) did not. Sevoflurane-induced maximal inhibition (at 3 minimum alveolar anesthetic concentration) on amplitude and frequency of spontaneous myometrial contractions in the presence of TEA (3.10^-4 M) was 31.85% and 22.33% of control contractions, respectively (P < 0.05). These results suggest that the in vitroapplication of sevoflurane inhibited the amplitude and frequency of spontaneous myometrial contractions in pregnant rats in a concentration-dependent manner. Such inhibition was reduced by TEA. The inhibition of myometrial smooth muscle induced by sevoflurane seems to be mediated, at least in part, via activation of Ca²⁺-activated K⁺ channels, because inhibition was reduced by TEA.

IMPLICATIONS: In this study, we found that sevoflurane causes significantly decreased myometrial contractile activity in pregnant rats. The inhibition of myometrial smooth muscle induced by sevoflurane seems to be mediated, at least in part, via activation of Ca²⁺-activated K⁺ channels, because inhibition was reduced by tetraethylammonium.

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