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.

Mechanisms of PTH-induced rise in cytosolic calcium in adult rat hepatocytes

1994 ◽  
Vol 267 (5) ◽  
pp. G754-G763 ◽  
Author(s):  
M. Klin ◽  
M. Smogorzewski ◽  
H. Khilnani ◽  
M. Michnowska ◽  
S. G. Massry
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Protein Kinase A ◽  
G Protein ◽  
Cytosolic Calcium ◽  
Amino Terminal ◽  
Kinase C ◽  
Dose Dependent ◽  
Kinase A ◽  
Stimulation Of

Available data indicate that the liver is a target organ for parathyroid hormone (PTH) and that this effect is most likely mediated by PTH-induced calcium entry into hepatocytes. The present study examined the effects of both PTH-(1-84) and its amino-terminal fragment [PTH-(1-34)] on cytosolic calcium concentration ([Ca2+]i) of hepatocytes and explored the cellular pathways that mediate this potential action of PTH. Both moieties of PTH produced a dose-dependent rise in [Ca2+]i, but the effect of PTH-(1-84) was greater (P < 0.01) than an equimolar amount of PTH-(1-34). This effect required calcium in the medium and was totally [PTH-(1-34)] or partially [PTH-(1-84)] blocked by PTH antagonist ([Nle8,18,Tyr34]bPTH-(7-34)-NH2] and by verapamil or nifedipine. Sodium or chloride channel blockers did not modify this effect. 12-O-tetradecanoylphorbol 13-acetate (TPA), an activator of protein kinase C, dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP), and G protein activator also produced a dose-dependent rise in [Ca2+]i. Staurosporine abolished the effect of TPA, and both staurosporine and calphostin C partially inhibited the effect of PTH. Staurosporine and verapamil together produced greater inhibition of PTH action than each alone. Rp-cAMP, a competitive inhibitor of cAMP binding to the R subunit of protein kinase A, and N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89), a protein kinase A inhibitor, blocked the effect of both DBcAMP and PTH, but the effect of these agents was greater (P < 0.01) on DBcAMP action. G protein inhibitor and pertussis toxin partially blocked the action of PTH. The data indicate that 1) PTH increases [Ca2+]i of hepatocytes; 2) this action of the hormone is receptor mediated; 3) the predominant pathway for this PTH action is the stimulation of a G protein-adenylate cyclase-cAMP system, which then leads to stimulation of a calcium transport system inhibitable by verapamil or nifedipine or activation of L-type calcium channels; 4) activation of protein kinase C is also involved; and 5) the PTH-induced rise in [Ca2+]i is due, in major parts, to movement of extracellular calcium into the cell.

scholarly journals G-protein βγ subunits antagonize protein kinase C-dependent phosphorylation and inhibition of phospholipase C-β1

1997 ◽  
Vol 326 (3) ◽  
pp. 701-707 ◽  
Author(s):  
Irene LITOSCH
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Phospholipase C ◽  
G Protein ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Negative Feedback Regulation ◽  
Kinase C ◽  
Stimulation Of

Protein kinase C (PKC) isoforms phosphorylated phospholipase C-β1 (PLC-β1) in vitro as follows: PKCα ≫ PKCϵ; not PKCζ. PLC-β3 was not phosphorylated by PKCα. G-protein βγ subunits inhibited the PKCα phosphorylation of PLC-β1 in a concentration-dependent manner. Half-maximal inhibition occurred with 500 nM βγ. G-protein βγ subunits also antagonized the PKCα-mediated inhibition of PLC-β1 enzymic activity. PKCα, in turn, inhibited the stimulation of PLC-β1 activity by βγ. There was little effect of PKCα on the stimulation of PLC-β1 by αq/11–guanosine 5′[γ-thio]triphosphate (GTP[S]). These findings demonstrate that G protein βγ subunits antagonize PKCα regulation of PLC-β1. Thus βγ subunits might have a role in modulating the negative feedback regulation of this signalling system by PKC.

scholarly journals Inhibitors of protein kinase C prolong the falling phase of each free-calcium transient in a hormone-stimulated hepatocyte

1990 ◽  
Vol 268 (3) ◽  
pp. 627-632 ◽  
Author(s):  
A Sanchez-Bueno ◽  
C J Dixon ◽  
N M Woods ◽  
K S R Cuthbertson ◽  
P H Cobbold
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Time Course ◽  
Phorbol Esters ◽  
Calcium Transient ◽  
Free Calcium ◽  
Hormone Concentration ◽  
Rat Hepatocyte ◽  
Pkc Inhibitor ◽  
Kinase C

Many cells generate oscillations in cytoplasmic free Ca2+ concentration (‘free Ca’) when stimulated with Ca-mobilizing hormones. The frequency of repetitive free-Ca transients in a rat hepatocyte is a function of hormone concentration and can be depressed by phorbol esters. We show here that the protein kinase C (PKC) inhibitors staurosporine and sphingosine can reverse the effects of phorbol dibutyrate on the frequency of free-Ca transients induced by phenylephrine or vasopressin. An important feature of the hepatocyte free-Ca oscillator is that the transient's time course, particularly the rate of fall of free Ca from peak to resting, depends on the species of agonist, and is measurably different for phenylephrine, vasopressin, angiotensin II or ATP. We show here that the rate of fall of free Ca in transients induced by phenylephrine or vasopressin is markedly decreased after treatment of the cells with a PKC inhibitor. A receptor-controlled oscillator model is discussed, in which PKC provides negative feedback during the falling phase of free-Ca transients.

ANP stimulates phospholipase C in cultured RIMCT cells: roles of protein kinases and G protein

1991 ◽  
Vol 260 (4) ◽  
pp. F590-F595 ◽  
Author(s):  
T. Berl ◽  
J. Mansour ◽  
I. Teitelbaum
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Protein Kinases ◽  
G Protein ◽  
Pertussis Toxin ◽  
Cyclic Nucleotide ◽  
Dependent Protein Kinase ◽  
Kinase C ◽  
Dependent Protein ◽  
Stimulation Of

We examined the possibility that, in addition to stimulation of guanylate cyclase (GC), atrial natriuretic peptide (ANP) also activates phospholipase C (PLC) in cultured rat inner medullary collecting tubule (RIMCT) cells. ANP (10(-12)M) causes marked release of inositol trisphosphate (IP3) at a concentration that does not stimulate GC. Concentrations of ANP that stimulate GC (greater than or equal to 10(-10) M) result in attenuated IP3 release. Similarly, exogenous dibutyryl guanosine 3',5'-cyclic monophosphate (10(-6) M) markedly inhibits the response to 10(-10) M ANP. Inhibition of cyclic nucleotide-dependent protein kinase by H 8, but not inhibition of protein kinase C by H 7, restores the response to 10(-8) and 10(-6) M ANP. Therefore, activation of cyclic nucleotide-dependent protein kinase inhibits ANP-stimulated PLC activity. Activation of protein kinase C by phorbol 12-myristate-13-acetate (PMA) decreases ANP-stimulated IP3 production. Pretreatment with H 7, but not H 8, prevents inhibition by PMA. To explore a potential role for G proteins, we examined the effect of guanine nucleotide analogues on ANP-stimulated IP3 production in saponin-permeabilized cells. ANP-stimulated IP3 production is enhanced by GTP gamma S and is inhibited by GDP beta S. Similarly, preincubation with pertussis toxin prevents ANP-stimulated IP3 release. We conclude that ANP stimulates PLC in RIMCT cells via a pertussis toxin-sensitive G protein. Stimulation of PLC is inhibited on activation of either cyclic nucleotide or Ca2+-phospholipid dependent protein kinases.

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 Effects of chemotactic factors and other agents on the amounts of actin and a 65,000-mol-wt protein associated with the cytoskeleton of rabbit and human neutrophils.

1985 ◽  
Vol 101 (1) ◽  
pp. 182-188 ◽  
Author(s):  
R Yassin ◽  
J Shefcyk ◽  
J R White ◽  
W Tao ◽  
M Volpi ◽  
...  
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Leukotriene B4 ◽  
Intracellular Concentration ◽  
Human Neutrophils ◽  
Free Calcium ◽  
High Osmolarity ◽  
Kinase C ◽  
Chemotactic Factors ◽  
Stimulation Of

Stimulation of rabbit neutrophils by the chemotactic factors fMet-Leu-Phe and leukotriene B4, by platelet activating factor, or by arachidonic acid produces a rapid and dose-dependent increase in the amounts of actin and of a 65,000-mol-wt protein associated with the cytoskeleton. Phorbol 12-myristate, 13-acetate, the calcium ionophore A23187 in the presence or absence of EGTA, and the fluorescent calcium chelator quin-2 also cause an increase in cytoskeletal actin. The stimulated increases in the cytoskeletal actin are not dependent on a rise in the intracellular concentration of free calcium and are not mediated by an increase in the intracellular pH or activation of protein kinase C. The increases in the cytoskeletal actin produced by fMet-Leu-Phe and leukotriene B4, but not by phorbol 12-myristate, 13-acetate, are inhibited by high osmolarity. The effect of hyperosmolarity requires a decrease in cell volume, is not mediated by an increase in basal intracellular concentration of free calcium, and is not prevented by pretreating the cells with amiloride. Preincubation of the cells with hyperosmotic solution also inhibits degranulation produced by all the stimuli tested. The inhibitory action of high osmolarity on the fMet-Leu-Phe and leukotriene B4 induced stimulation of cytoskeletal actin is discussed in terms of the possibility that the addition of high osmolarity, either directly or through activation of protein kinase C, causes receptor uncoupling.

scholarly journals Mastoparan promotes exocytosis and increases intracellular cyclic AMP in human platelets. Evidence for the existence of a Ge-like mechanism of secretion

1992 ◽  
Vol 281 (2) ◽  
pp. 465-472 ◽  
Author(s):  
C P D Wheeler-Jones ◽  
T Saermark ◽  
V V Kakkar ◽  
K S Authi
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Cyclic Amp ◽  
G Protein ◽  
Human Platelets ◽  
Dependent Manner ◽  
Kinase C ◽  
Reversible Electroporation ◽  
Dose Dependent ◽  
Stimulation Of

Recent studies have shown that mastoparan, an amphiphilic peptide derived from wasp venom, accelerates guanine nucleotide exchange and GTPase activity of purified GTP-binding proteins. In the present study we have examined the functional consequences of exposure of intact human platelets to mastoparan. Mastoparan promoted rapid (less than or equal to 1 min) dose-dependent increases in 5-hydroxy[14C]tryptamine and beta-thromboglobulin release from dense-granule and alpha-granule populations respectively. The exocytotic response did not result from a lytic effect of mastoparan and occurred in the complete absence of platelet shape change and aggregation. Liberation of [3H]arachidonate and increases in cytosolic [Ca2+] (detected with fura 2) were not observed in platelets stimulated with mastoparan. Similarly, in platelets preloaded with [3H]inositol during reversible electroporation, mastoparan did not cause the accumulation of [3H]inositol phosphates. Mastoparan-induced secretion was unaffected by preincubation with either the protein kinase C inhibitor staurosporine (10 nM-10 microM) or prostacyclin (PGI2; 100 ng/ml) and was not accompanied by phosphorylation of the 45 kDa protein kinase C substrate or the 20 kDa protein normally associated with platelet activation. The G-protein inhibitor guanosine 5′-[beta-thio]diphosphate (GDP[S]; 1 mM) attenuated the secretion induced by mastoparan in both intact and saponin-permeabilized platelets. Encapsulation of GDP[S] during reversible permeabilization inhibited mastoparan-induced secretion, providing evidence for an intracellular action of GDP[S]. In all these studies thrombin (0.05-0.2 unit/ml) elicited characteristic responses, and thrombin-induced secretion was inhibited by staurosporine, PGI2 and GDP[S]. Mastoparan also increased intra-platelet cyclic AMP in a dose-dependent manner. Mastoparan and PGI2 increased 32P incorporation into a protein of approx. 24 kDa, whereas phosphorylation of a 50 kDa substrate was only seen in PGI2-stimulated platelets. These results indicate that mastoparan promotes secretion by a mechanism which does not involve stimulation of phospholipase C and suggest that the secretory event may result either from a direct fusogenic action of mastoparan and/or from stimulation of the putative exocytosis-linked G-protein, Ge.

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.

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