Possible involvement of a small G-protein sensitive to exoenzyme C3 of Clostridium botulinum in the regulation of myofilament Ca2+ sensitivity in beta-escin skinned smooth muscle of guinea pig ileum.
The effects of exoenzyme C3 of Clostridium botulinum on Ca(2+)- and drug-induced tension developments were investigated in beta-escin skinned smooth muscle of guinea pig ileum to test the involvement of a small G-protein in the regulation of myofilament Ca2+ sensitivity. C3 is known to ADP-ribosylate the rho p21 family of small G-proteins. Treatment with C3 (0.35 microgram/ml, for 30 min) shifted the pCa-tension curve rightward along the Ca2+ concentration axis, indicating a decrease in Ca2+ sensitivity of the contractile elements. The inhibitory effect of C3 was not preserved after treatment with GDP beta S (1 mM), an antagonist of GTP for the binding to G-proteins. Stimulation of muscarinic receptors with carbachol (CCh, 100 microM) shifted the pCa-tension curve leftward, indicating Ca2+ sensitization of tension development. The Ca(2+)-sensitizing effect of CCh was not observed after C3 treatment. When GTP gamma S (10 microM), an activator of G-proteins, was applied at a plateau of tension development produced by a moderate concentration of Ca2+, further increase in tension was elicited and the effect of GTP gamma S was inhibited by C3 treatment. The results suggest the possible involvement of a rho p21-like small G-protein in the regulation of Ca2+ sensitivity of smooth muscle myofilaments.
Itagaki
M
M
Department of Veterinary Science, Faculty of Agriculture, Gifu University, Japan.
Komori
S
S
Unno
T
T
Syuto
B
B
Ohashi
H
H
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol; D003176:Complement C3 / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000502:physiology*; D006160:Guanosine Triphosphate; D006168:Guinea Pigs; D007082:Ileum / Q000502:physiology; D008297:Male; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000502:physiology*
D003176:Complement C3; D006160:Guanosine Triphosphate; D002217:Carbachol; D019204:GTP-Binding Proteins; D002118:Calcium