Mechanisms of isoflurane-increased submaximum Ca2+-activated force in rabbit skinned femoral arterial strips

Isoflurane enhances contraction in isolated intact arterial rings by a protein kinase C (PKC) activator and also causes contracture in skinned arterial strips. This study investigated the mechanisms of this isoflurane activation of the contractile proteins of skinned strips.

The skinned strips, mounted on photodiode force transducers, were prepared from rabbit femoral arteries treated with saponin. The strips were activated by 1 microM Ca2+ (buffered with 7 mM EGTA) with or without inhibitors for PKC and calmodulin-dependent protein kinase II (CaM kinase II). When force reached steady state, isoflurane was administered and changes in force were observed. Another group of the strips was frozen to assay myosin light chain phosphorylation (MLC-p) using two-dimensional electrophoresis and immunoblotting. Analysis of variance was used to compare the results from test and control groups. Probability values <0.05 were significant.

Isoflurane (1-5%) dose dependently increased (24-81%) the Ca2+-activated force. At 1% and 5% isoflurane, MLC-p did not change either as the force increased or reached a new steady state level. However, with 3% isoflurane, MLC-p transiently decreased (29.1% and 17.1% of total MLC for 0% and 3% isoflurane, respectively). The 3% isoflurane-increased force was blocked by 10 microM bisindolymaleidmide, an inhibitor of PKC, but not by 10 microM Gö-6976, an inhibitor of Ca2+-dependent PKC, and was enhanced 50% by 0.1 mM KN-62, an inhibitor of CaM kinase II.

Isoflurane increased submaximum Ca2+-activated force in skinned femoral arterial strips by activating Ca2+-independent PKC, possibly epsilon isoezyme. The isoflurane-decreased MLC-p may be caused by activation of CaM kinase II.