Contractile dysfunction in K ATP channel deficient muscle during fatigue involves Ca 2+ influx and reactive oxygen species

Abstract

A previous study has shown that KATP channel deficient muscles have faster rate of fatigue than wild type muscles and that the apparent faster fatigue rate was probably because of several contractile dysfunctions that include large increases in resting [Ca2+]i and resting tension as well as poor force recovery after fatigue. The objective of this study was to test the hypothesis that the contractile dysfunctions are due to a Ca2+ influx thought L-type Ca2+ channels and increased production of reactive oxygen species (ROS). To test this hypothesis, FDB muscle bundles from wild type and Kir6.2−/− mice, which has no KATP channel activity in the cell membrane, were fatigued with one contraction per sec for 3 min. Lowering [Ca2+]e from 2.4 mM (control) to 0.6 mM or adding 20 μM verapamil, to partially blocked L-type Ca2+ channels, reduced the increased in resting tension in Kir6.2−/− FDB and improved force recovery, while it had no effects in wild type FDB. Exposing Kir6.2−/− FDB to 10 mM NAC or triron, two ROS scavengers, also reduced resting tension and improve force recovery in Kir6.2−/− FDB. Furthermore, exposing Kir6.2−/− FDB to either low [Ca2+]e, verapamil, NAC or triron had no effect on the pre-fatigue peak tetanic force, but significantly reduced the rate of fatigue whereas it had absolutely not effect in wild type FDB. It is therefore concluded that the contractile dysfunctions in Kir6.2−/− FDB involved a Ca2+ influx through L-type Ca2+channels and the production of ROS. Our data also suggest that the contractile dysfunctions are also responsible for the apparent faster rate of fatigue in KATP channel deficient muscle.