Inhibition of the contraction of the isolated longitudinal muscle of the guinea-pig ileum by botulinum C2 toxin: Evidence for a role of G/F-actin transition in smooth muscle contraction

Abstract

The effect of botulinum C2 toxin was studied on the contractions of the guinea pig ileum myenteric plexus longitudinal muscle preparation. Botulinum C2 toxin inhibited the muscle contraction induced by electrical stimulation (60 V; 0.5 ms; 0.33 Hz) in a time and concentration dependent manner. The inhibitory effect occurred with a time lag of about 1 h, and depended on the presence of both toxin components. After 4 h of incubation with 1.7 micrograms/ml of component I and 6.7 micrograms/ml of component II of botulinum C2 toxin, the smooth muscle contraction was inhibited by about 60%. At these toxin concentrations, about 55% of the modifiable smooth muscle actin was ADP-ribosylated. Smooth muscle contraction induced by bradykinin and bethanechol were similarly inhibited. Moreover, the C2 toxin inhibited muscle contraction induced by Ba2+, and by direct muscle membrane depolarization (60 V; 10 ms; 0.33 Hz) after suppression of acetylcholine release by normorphine. Also cytochalasin D inhibited the electrically evoked contraction of the ileum longitudinal muscle. In contrast to botulinum C2 toxin, inhibition of contractility by cytochalasin D occurred without a lag phase, and was reversed by washing off the toxin. In contrast of guinea pig ileum longitudinal muscle, botulinum C2 toxin did not reduce the contraction of the rabbit aortic smooth muscle stimulated by K+-depolarization or noradrenaline.

Cytoskeletal remodeling in differentiated vascular smooth muscle is actin isoform dependent and stimulus dependent

“…However, ␥-actin does show significant isoformdependent remodeling during PE contractions. Similarly, Mauss et al (39) have shown that ileal smooth muscle, but not VSM, contractility is inhibited by botulinum C2 toxin. This toxin ADP ribosylates G-actin of ␥-but not ␣-smooth muscle actin isoforms (38).…”

ADP-ribosylation of actin

“…Recently, it has been shown that botulinum C2 toxin inhibits the contraction of the isolated longitudinal muscle of the guinea pig ileum most probably by a direct interaction with the smooth muscle cells (Mauss et al, 1989). Since G-actin but not F-actin is a substrate of C2 toxin these findings indicate a role of G/F-actin transition in smooth contraction corroborating a similar observation with cytochalasin (Adler et aI., 1983).…”

Clostridial ADP-ribosyltransferases ? Modification of low molecular weight GTP-binding proteins and of actin by clostridial toxins

“…C2 toxin inhibited the contraction of the longitudinal smooth muscle of the guinea pig ileum (Mauss et al 1989). This effect was most probably caused by a direct action of the toxin on the smooth muscle cell.…”