scholarly journals Down-regulation of G-protein-mediated Ca2+ sensitization in smooth muscle.

1997 ◽  
Vol 8 (2) ◽  
pp. 279-286 ◽  
Author(s):  
M C Gong ◽  
H Fujihara ◽  
L A Walker ◽  
A V Somlyo ◽  
A P Somlyo
Keyword(s):  
Smooth Muscle ◽  
Protein Kinase C ◽  
Protein Kinase ◽  
G Protein ◽  
Total Content ◽  
Prolonged Treatment ◽  
Down Regulation ◽  
Kinase C ◽  
G Alpha Q ◽  
Gamma S

Prolonged treatment with guanosine 5'-[gamma-thio]triphosphate (GTP gamma S; 5-16 h, 50 microM) of smooth muscle permeabilized with Staphylococcus aureus alpha-toxin down-regulated (abolished) the acute Ca2+ sensitization of force by GTP gamma S, AIF-4, phenylephrine, and endothelin, but not the response to phorbol dibutyrate or a phosphatase inhibitor, tautomycin. Down-regulation also abolished the GTP gamma S-induced increase in myosin light chain phosphorylation at constant [Ca2+] and was associated with extensive translocation of p21rhoA to the particulate fraction, prevented its immunoprecipitation, and inhibited its ADP ribosylation without affecting the immunodetectable content of G-proteins (p21rhoA, p21ras, G alpha q/11, G alpha i3, and G beta) or protein kinase C (types alpha, beta 1, beta 2, delta, epsilon, eta, theta, and zeta). We conclude that the loss of GTP gamma S- and agonist-induced Ca2+ sensitization through prolonged treatment with GTP gamma S is not due to a decrease in the total content of either trimeric (G alpha q/11, G alpha i3, and G beta) or monomeric (p21rhoA and p21ras) G-protein or protein kinase C but may be related to a structural change of p21rhoA and/or to down-regulation of its (yet to be identified) effector.

scholarly journals Down-regulation of protein kinase C potentiates angiotensin II-stimulated polyphosphoinositide hydrolysis in vascular smooth-muscle cells

1989 ◽  
Vol 262 (1) ◽  
pp. 285-291 ◽  
Author(s):  
J Pfeilschifter ◽  
M Ochsner ◽  
S Whitebread ◽  
M De Gasparo
Keyword(s):  
Smooth Muscle ◽  
Protein Kinase C ◽  
Angiotensin Ii ◽  
Protein Kinase ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
Down Regulation ◽  
Subsequent Formation ◽  
Kinase C ◽  
Protein Kinase C Activity

In smooth-muscle cells (SMC) isolated from rat aorta, angiotensin II stimulates a phospholipase C with subsequent formation of inositol trisphosphate (InsP3). Short-term (10 min) pretreatment of SMC with 12-O-tetradecanoylphorbol 13-acetate (TPA; 100 nM) decreases the angiotensin II-induced InsP3 formation. However, this inhibition is not observed after incubating the cells for 2 h with TPA. Longer-term pretreatments even lead to an enhanced generation of InsP3. This increased response to angiotensin II occurs without a significant change in the receptor number or Kd value of angiotensin II binding to the cells. The biologically inactive phorbol ester 4 alpha-phorbol 12,13-didecanoate was without effect on angiotensin II-stimulated InsP3 generation, irrespective of the time of preincubation. In parallel with this potentiation of angiotensin II-induced generation of InsP3 by TPA, a down-regulation of protein kinase C activity is observed. A 24 h pretreatment of SMC with TPA decreases protein kinase C activity to less than 10% of that of control cells. Longer-term pretreatment also increases the angiotensin II-induced release of Ca2+ and delays the decay of the transient Ca2+ increase. All these data suggest that protein kinase C exerts a negative feedback control on angiotensin II-stimulated polyphosphoinositide turnover, and that protein kinase C is an important factor in limiting the production of InsP3 in stimulated cells.

scholarly journals Guanosine 5'-thiotriphosphate may stimulate phosphoinositide messenger production in sea urchin eggs by a different route than the fertilizing sperm.

1991 ◽  
Vol 2 (2) ◽  
pp. 121-133 ◽  
Author(s):  
I Crossley ◽  
T Whalley ◽  
M Whitaker
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
G Protein ◽  
Sea Urchin ◽  
Calcium Transient ◽  
Free Calcium ◽  
Sea Urchin Eggs ◽  
Kinase C ◽  
Gamma S ◽  
Stimulation Of

We show that microinjecting guanosine-5'-thiotriphosphate (GTP gamma S) into unfertilized sea urchin eggs generates an intracellular free calcium concentration [( Ca]i) transient apparently identical in magnitude and duration to the calcium transient that activates the egg at fertilization. The GTP gamma S-induced transient is blocked by prior microinjection of the inositol trisphosphate (InsP3) antagonist heparin. GTP gamma S injection also causes stimulation of the egg's Na+/H+ antiporter via protein kinase C, even in the absence of a [Ca]i increase. These data suggest that GTP gamma S acts by stimulating the calcium-independent production of the phosphoinositide messengers InsP3 and diacylglycerol (DAG). However, the fertilization [Ca]i transient is not affected by heparin, nor can the sperm cause calcium-independent stimulation of protein kinase C. It seems that the bulk of InsP3 and DAG production at fertilization is triggered by the [Ca]i transient, not by the sperm itself. GDP beta S, a G-protein antagonist, does not affect the fertilization [Ca]i transient. Our findings do not support the idea that signal transduction at fertilization operates via a G-protein linked directly to a plasma membrane sperm receptor.

A hypothesis for the mechanism of receptor and G-protein-dependent enhancement of vascular smooth muscle myofilament Ca2+ sensitivity

1994 ◽  
Vol 72 (11) ◽  
pp. 1420-1426 ◽  
Author(s):  
Anikó Rokolya ◽  
Hee Yul Ahn ◽  
Suzanne Moreland ◽  
Cornelis van Breemen ◽  
Robert S. Moreland
Keyword(s):  
Smooth Muscle ◽  
Protein Kinase C ◽  
Steady State ◽  
Protein Kinase ◽  
G Protein ◽  
Kinase C ◽  
Agonist Stimulation ◽  
Cross Bridges ◽  
Mlc Phosphorylation ◽  
Stimulation Of

Agonist activation enhances smooth muscle myofilament Ca2+ sensitivity. The increased force accompanying receptor stimulation (over Ca2+ alone) requires GTP and is reversed by GDPβS, demonstrating a G-protein dependence. Protein kinase C (PKC) activators, such as phorbol esters, mimic and PKC inhibitors block the agonist-induced increase in Ca2+ sensitivity, suggesting a role for PKC in the regulation of Ca2+ sensitivity. Myosin light chain (MLC) phosphorylation levels are transiently increased by agonist stimulation, but steady-state levels of MLC phosphorylation are similar to those in response to Ca2+ alone. Thus, G-protein-mediated inhibition of MLC phosphatase may account for the initial increase in force development but not the increase in steady-state force. In contrast to MLC, calponin phosphorylation levels are maintained during agonist stimulation of intact vascular smooth muscle. We propose that stimulation of smooth muscle by membrane depolarization increases MLC phosphorylation, but as a result of inhibition by unphosphorylated calponin only a portion of the phosphorylated cross bridges attach to actin. Agonist stimulation produces the same steady-state level of MLC phosphorylation but also leads to calponin phosphorylation via a PKC-dependent pathway. Thus, during agonist stimulation, all phosphorylated cross bridges can interact with actin, thereby generating significantly greater levels of force.Key words: β-toxin, permeabilized smooth muscle, calcium, calponin, phosphorylation, sensitization, protein kinase C, mesenteric artery, endothelin.

scholarly journals A novel mechanism for the Ca(2+)-sensitizing effect of protein kinase C on vascular smooth muscle: inhibition of myosin light chain phosphatase.

1994 ◽  
Vol 104 (2) ◽  
pp. 265-286 ◽  
Author(s):  
M Masuo ◽  
S Reardon ◽  
M Ikebe ◽  
T Kitazawa
Keyword(s):  
Smooth Muscle ◽  
Protein Kinase C ◽  
Protein Kinase ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Force Development ◽  
Kinase C ◽  
Sensitizing Effect ◽  
Mlc Phosphorylation ◽  
Gamma S

Mechanisms of Ca2+ sensitization of both myosin light chain (MLC) phosphorylation and force development by protein kinase C (PKC) were studied in permeabilized tonic smooth muscle obtained from the rabbit femoral artery. For comparison, the Ca2+ sensitizing effect of guanosine 5'-O-(gamma-thiotriphosphate) (GTP gamma S) was examined, which had been previously shown to inhibit MLC phosphatase in phasic vascular smooth muscle. We now report that PKC activators (phorbol esters, short chain synthetic diacylglycerols and a diacylglycerol kinase inhibitor) and GTP gamma S significantly increase both MLC phosphorylation and force development at constant [Ca2+]. Major phosphorylation site occurring in the presence of phorbol-12,13-dibutyrate (PDBu) or GTP gamma S at constant [Ca2+] is the same serine residue (Ser-19) as that phosphorylated by MLC kinase in response to increased Ca2+ concentrations. In an ATP- and Ca(2+)-free solution containing 1-(5-chloronaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine (ML-9), to avoid the kinase activity, both PDBu and GTP gamma S significantly decreased the rate of MLC dephosphorylation to half its control value. However, PDBu inhibited the relaxation rate more than did GTP gamma S. In the presence of microcystin-LR to inhibit the phosphatase activity, neither PDBu nor GTP gamma S affected MLC phosphorylation and force development. These results indicate that PKC, like activation of GTP binding protein, increases Ca2+ sensitivity of both MLC phosphorylation and force production through inhibition of MLC phosphatase.

Sign in / Sign up

Export Citation Format

Share Document