Excitatory effect of Clostridium perfringens alpha toxin on the rat isolated aorta

Abstract

Clostridium perfringens alpha toxin caused contraction of the isolated aorta of the rat in a dose‐dependent manner. The contractile action caused by the toxin was inhibited or abolished by calcium antagonists such as nifedipine, verapamil and cinnarizine, or a Ca‐free medium, but was not affected by phentolamine, chlorpheniramine, atropine, tetrodotoxin or a low Na medium. The toxin stimulated Ca uptake into the aorta in a dose‐dependent manner. 8‐N,N'‐diethylaminooctyl‐3,4,5‐trimethoxybenzoate (TMB‐8) blocked significantly both the toxin‐ and noradrenaline (NA)‐induced contractions. Trifluoperazine (TFP) and N‐(6‐aminohexyl)‐5‐chloro‐l‐naphtharene sulphonamide (W‐7) did not affect the contractile activity of the toxin but blocked the NA‐induced contraction. The toxin also stimulated the 32P phosphate labelling of phosphatidylinositol (PI) and phosphatidic acid (PA) in the preparation. These results indicate that the toxin‐induced contraction, which is different from that induced by NA, is the result of a direct action of the toxin on the aorta and is due to an increased Ca2+ permeability across the smooth muscle membrane. It is suggested that the contractile response to the toxin is associated with activation of phospholipid metabolism and enhanced entry of Ca into the aorta.

Role of Phospholipid Metabolism and G Protein in the Action Induced by Clostridium Perfringens Alpha-Toxin

“…The response to the toxin therefore seems to be the result of a direct effect on the aorta. Alpha-toxin-induced contractions were inhibited by Ca channel blockers such as verapamil and nifedipine [16]. Furthermore, the toxin-induced contractionswere not observed in Ca-free medium.…”

“…Thus, the toxin-induced contractions of the isolated rat aorta associated with the production of TXA 2 required an intact endothelium. Furthermore, TMB-8 (intracellular Ca 2+ antagonist), trifluoperazine, W-7(calmodulin inhibitor) and H-7 (PKC inhibitor) significantly blocked the toxininduced contractions [16]. From these observations, in endothelial cells of the rat aorta, alpha-toxin stimulates phosphotidylinositol metabolism and arachidonic acid release, leading to the production of TXA 2 and the phosphorylation of myosin light chain which then elicits contractions of the adjacent aorta smooth muscle ( Figure 2).…”

“…The data indicate that the direct action of the toxin is mainly due to an increase in Ca permeability across the smooth muscle cell membranes [16]. Labelling by 32 P phosphate of phosphatidylinositol (PI) and phosphatidic acid (PA) in fragments of the aorta was enhanced by alpha-toxin [16]. Therefore, Ca influx caused by the toxin is thought to be associated with the stimulation of phospholipid metabolism.…”

“…The toxin caused contractions of the isolated rat aorta in a dose-dependent manner [16]. The response to repeated doses of the toxin was found to be tachyphylactic.…”

“…We have reported that the alpha-toxin-induced contraction of isolated rat aorta and ileum [16][17][18], and hemolysis of rabbit erythrocytes [19][20][21] are dependent on the activation of glycerophospholipid metabolism. We have also demonstrated that the alpha-toxin-induced hemolysis of sheep erythrocytes is dependent on the activation of the sphingomyelin metabolic system through GTP-binding proteins, especially the formation of sphingosine 1-phosphate [22,23].Therefore, the toxin-induced activation of phospholipid metabolism through G protein is closely involved in the biological activities.…”