Ras proteins increase Ca²⁺‐responsiveness of smooth muscle contraction

Abstract

G‐proteins may be involved in receptor‐mediated Ca2+‐sensitization of smooth muscle contraction, but the responsible G‐proteins are not yet known. Here we show that in β‐escin skinned mesenteric microarteries, H‐ras p21 proteins, preactivated with GTP or GTP γ S, increase force at constant submaximal Ca2+ (pCa 6.3) concentration dependently. The GTP‐bound form of the wild‐type H‐ras p21 and the oncogenic mutant (p21[G12V]) were equally effective. The nucleotide‐free and the inactive GDP‐bound form of ras p21 had no effect on force. The tyrosine kinase inhibitor, tyrphostin, partially reversed the effect of the ras proteins in the GTP‐bound form on force. Thus, ras proteins mimic the Ca2+‐sensitizing effect of GTPγS and vasoconstrictors in mesenteric microarteries which may involve tyrosine phosphorylation.

Small G Proteins in the Cardiovascular System: Physiological and Pathological Aspects

“…(Figure 4) A) RAS. The first demonstration of a role of Ras in the regulation of smooth muscle contraction was provided by the observation that active H-Ras induces tension of permeabilized arteries by increasing the Ca 2ϩ responsiveness in a concentration-dependent manner (416). Downstream of Ras, ERK1/2 activation triggers MLCK phosphorylation, leading to an increase in its sensitivity to calmodulin and, consequently, its ability to phosphorylate MLC (227).…”

Role of guanine nucleotide-binding proteins--ras-family or trimeric proteins or both--in Ca2+ sensitization of smooth muscle.

“…We used a mutated vall4p2lrhoA that, because of its very low GTPase activity, is constitutively active in its GTP-bound form (36), eliminating effects due to release of free GTP[y-S] from wild-type p2lrhoA. Constitutively active vall4p2lrhoA caused contraction at constant [Ca2+] and, although such an effect can also be produced by H-ras p21 (12), by detergents (0.3% Na cholate) (M.C.G., S.K., A.V.S., and A.P.S., unpublished observations), and even by some batches of bovine serum albumin (M.C.G., S.K., A.V.S., and A.P.S., unpublished observations), the inhibition of the Ca2+-sensitizing effect of vall4p2lrho by ADP-ribosylation in vitro supports its specificity of action, as do the inhibitory effects of ADP-ribosylation of endogenous p2lrhoA on Ca2+ sensitization by GTP, carbachol, and endothelin (Fig. 3).…”

“…This process of Ca2+ sensitization can be inhibited by guanosine 5'-[,B-thioldiphosphate (GDP[/3-S]) (5)(6)(7)(8), but the G protein(s) involved and the transduction pathways between plasma membrane-bound receptors and the myosin filamentbound protein phosphatase (9)(10)(11) have not been definitively identified. Both a constitutively active ras (12) and p2lrhoA activated with guanosine 5'-[y-thio]triphosphate (GTP[-y-S]) (13,11) have been reported to Ca2+-sensitize smooth muscle,…”

Targeted Genomic Disruption of H-Ras Induces Hypotension Through a NO-cGMP-PKG Pathway–Dependent Mechanism

“…[7][8][9] Until recently, the relationships between Ras and the regulation of blood pressure have scarcely been studied. Previous reports suggested a role for Ras in the cellular response to angiotensin II, 10,11 but no definite relationship between this protein and blood pressure was established. However, genetic manipulation of the different isoforms of the Ras gene has underscored the relevance of this protein as a hemodynamic regulator.…”