The Rho-related protein Rnd1 inhibits Ca2+ sensitization of rat smooth muscle.
1. The small GTP-binding Rho proteins are involved in the agonist-induced Ca2+ sensitization of smooth muscle. The action and the expression of Rnd1, a new member of the Rho protein family constitutively bound to GTP, has been studied in rat smooth muscle. 2. Recombinant prenylated Rnd1 (0.01-0.1 mg ml-1) dose dependently inhibited carbachol- and GTPgammaS-induced Ca2+ sensitization in beta-escin-permeabilized ileal smooth muscle strips but had no effect on the tension at submaximal [Ca2+] (pCa 6.3). Rnd1 inhibited GTPgammaS-induced tension without shifting the dose-response curves to GTPgammaS. 3. pCa-tension relationships were not modified by Rnd1 and the rise in tension induced through the inhibition of myosin light chain phosphatase by calyculin A was not affected by Rnd1. 4. The Ca2+ sensitization induced by recombinant RhoA was completely abolished when RhoA and Rnd1 were applied together. 5. Rnd1 was expressed at a low level in membrane fractions prepared from intestinal or arterial smooth muscles. The expression of Rnd1 was strongly increased in ileal and aortic smooth muscle from rats treated with progesterone or oestrogen. Progesterone-treated ileal muscle strips showed a decrease in agonist-induced Ca2+ sensitization. 6. The present study shows that (i) Rnd1 inhibits agonist- and GTPgammaS-induced Ca2+ sensitization of smooth muscle by specifically interfering with a RhoA-dependent mechanism and (ii) an increase in Rnd1 expression may account, at least in part, for the steroid-induced decrease in agonist-induced Ca2+ sensitization.
Loirand
G
G
Institut de Pharmacologie Moleculaire et Cellulaire, CNRS UPR 411, 660 route des lucioles, Sophia Antipolis, 06560 Valbonne, France.
Cario-Toumaniantz
C
C
Chardin
P
P
Pacaud
P
P
D000818:Animals; D015153:Blotting, Western; D020013:Calcium Signaling / Q000187:drug effects*; D002217:Carbachol / Q000037:antagonists & inhibitors / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000096:biosynthesis / Q000494:pharmacology*; D012739:Gonadal Steroid Hormones / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000037:antagonists & inhibitors / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000378:metabolism; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D008387:Marine Toxins; D018721:Muscarinic Agonists / Q000494:pharmacology; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D010080:Oxazoles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D051381:Rats; D017208:Rats, Wistar; D011994:Recombinant Proteins / Q000494:pharmacology; D020741:rho GTP-Binding Proteins
D004791:Enzyme Inhibitors; D012739:Gonadal Steroid Hormones; D008387:Marine Toxins; D018721:Muscarinic Agonists; D010080:Oxazoles; D011994:Recombinant Proteins; C491771:Rnd1 protein, rat; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C059041:calyculin A; D006160:Guanosine Triphosphate; D002217:Carbachol; D010749:Phosphoprotein Phosphatases; D019204:GTP-Binding Proteins; D020741:rho GTP-Binding Proteins