CALMODULIN MEDIATES CONTRACTION OF THE OVIDUCTS OF LOCUSTA-MIGRATORIA

Calmodulin (CaM) is a multifunctional calcium binding protein which is an essential mediator in the contraction of mammalian smooth muscle. In the present study, evidence is provided that CaM is important in me diating insect visceral muscle contraction. Calmodulin is present in t he oviducts of the locust, Locusta migratoria, at c. 55 ng/mg protein, 2.7 times that found in the external ventral protractor of the VIIth abdominal segment, a skeletal muscle. The calmodulin inhibitors triflu operazine (TFP) and N-(6-aminohexyl)-5-chloro-l-naphthalenesulfonamide (W7) inhibited proctolin-inuced contractions in a dose-dependent mann er. The effective dose for 50% inhibition (ED(50)) of contraction for TFP was 1.6 x 10(-4) M and for W7 was 3.0 x 10(-4) M. High potassium-i nduced contractions were also inhibited dose-dependently by TFP and W7 with ED(50)s of 1.8 x 10(-4) M and 5.1 x 10(-4) M, respectively. The protein kinase C (PKC) inhibitor chelerythrine had no effect on either proctolin- or high potassium-induced contractions of the locust ovidu ct indicating that TFP and W7 were not simply antagonizing PKC in prod ucing their inhibitory effects. At least 15 calmodulin binding protein s (CaMBPs) were visualized in the locust oviduct muscle after probing SDS polyacrylamide gels with S-35-VU-1 CaM. Futhermore the binding of CaM to proteins in the gel was inhibited in a dose-dependent manner in the presence of either TFP or W7 paralleling the physiological inhibi tion of contraction. These results indicate that the contraction of th e locust oviducal muscle is, at least in part, mediated by calmodulin, possibly through a CaMBP such as myosin light chain kinase, similar t o the process of contraction in smooth muscles of vertebrates.