Relationship between structure of phenothiazine analogues and their activity on platelet calcium fluxes

Enouf, Jocelyne; Lévy-Toledano, S

doi:10.1111/j.1476-5381.1984.tb10104.x

Cited by 24 publications

(8 citation statements)

References 31 publications

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“…Human platelet membranes were prepared by a similar method, as described previously [33,42], and platelet membranes from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats were isolated as described by Papp et al [43].…”

Section: Membrane Preparationmentioning

confidence: 99%

Correlated expression of the 97 kDa sarcoendoplasmic reticulum Ca2+-ATPase and Rap1B in platelets and various cell lines

Magnier

Bredoux

Kovàcs

et al. 1994

Biochemical Journal

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Evidence has accumulated that cyclic AMP (cAMP)-induced phosphorylation of a Ras-related protein (Rap1) regulates platelet Ca2+ transport. As this transport was recently found to be controlled by two isoforms of sarcoendoplasmic reticulum Ca(2+)-ATPase (SERCA), the 100 kDa SERCA2b and the newly identified 97 kDa SERCA, we attempted to establish which isoform is involved in this regulation. For this purpose, we studied the expression and regulation of both the SERCA and Rap1 isoforms in platelets, haemopoietic cells and various cancer cell lines. SERCA2b was shown to be equally expressed in all the cell lines tested, as determined by detection of its phosphoenzyme formation and by Western blotting using an isoform-specific antibody. In contrast, the expression of the 97 kDa SERCA, studied by the same methods, varied from total absence in the cancer cells to high levels in the megakaryocytic cell lines. With regard to the potential regulatory Rap1 proteins, Western blotting showed different expression of total Rap1 isoforms among the cell lineages, thus ruling out any possible relationship between Rap1 and SERCA2b. However, the expression of Rap1 proteins correlated with that of the 97 kDa SERCA isoform. More refined analysis of the rap1A and rap1B isoforms by reverse transcription PCR and by determining cAMP-induced phosphorylation of Rap1B, i.e. its functional mechanism, confirmed the correlation between Rap1B and the 97 kDa SERCA expression. This relationship was also established by the concerted up-regulation of these two proteins demonstrated in the pathological model of platelets from hypertensive rats. It is concluded that the expressions of 97 KDa SERCA and Rap1B are related, suggesting that regulation of the platelet Ca(2+)-ATPase system by cAMP-induced phosphorylation of Rap1B specifically involves the 97 kDa SERCA.

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Section: Membrane Preparationmentioning

confidence: 99%

Correlated expression of the 97 kDa sarcoendoplasmic reticulum Ca2+-ATPase and Rap1B in platelets and various cell lines

Magnier

Bredoux

Kovàcs

et al. 1994

Biochemical Journal

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“…Ca2+-accumulating membrane vesicles were prepared as previously described [10,32]. Briefly, fresh platelets were isolated and washed in Tyrode's modified buffer.…”

Section: Preparation Of the Crude Platelet Membrane Fractionmentioning

confidence: 99%

The phosphoprotein that regulates platelet Ca2+ transport is located on the plasma membrane, controls membrane-associated Ca2+-ATPase and is not glycoprotein Ib β-subunit

Darnanville

Bredoux

Clemetson

et al. 1991

Biochemical Journal

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The localization and identity of the human platelet 24 kDa cyclic AMP (cAMP)-dependent phosphoprotein, previously reported to regulate Ca2+ transport, was investigated. It was found to be located on plasma membranes after isolation of these membranes from microsomes. Thus cAMP-dependent regulation of Ca2+ transport was associated with the plasma membrane fraction. Time course studies showed that the catalytic subunit of cAMP-dependent protein kinase (c-sub) induced a maximal 2-fold stimulation of Ca2+ uptake by the plasma membrane vesicles. This stimulation was dose-dependent up to 15 micrograms of c-sub/ml. The increase in Ca2+ uptake also depended upon the outside Ca2+ concentration, and was maximal at 1 microM. As regards the identity of the phosphoprotein, it was clearly distinct from the beta-subunit of glycoprotein Ib, as after electrophoresis under reduced conditions it appeared as a 24 kDa protein, but under non-reduced conditions it appeared as a 22 kDa and not as a 170 kDa protein. Nevertheless, glycoprotein Ib was certainly present, because it was detected with two polyclonal antibodies raised against its two subunits. Furthermore, the 24 kDa phosphoprotein was also present in membranes isolated from platelets obtained from patients with Bernard Soulier Syndrome; these membranes contain no glycoprotein Ib.

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“…vascular smooth muscle, although reported to promote Ca2+ sequestration within a microsomal fraction [22], the effects of cGMP on Ca2+ homeostasis are controversial [23]. Although phenothiazines inhibit Ca2+ uptake by the dense tubular system, such effects could not be attributed to an interaction with calmodulin [9]. However, phenothiazines are known to inhibit protein kinase C in platelets [lo].…”

Section: Methodsmentioning

confidence: 99%

“…The isolated dense tubular system actively accumulates Ca2+ and contains a (Ca'+ + Mg'+)-ATPase [7]. Sequestration of Ca2+ within this organelle is augmented by CAMP [8] and inhibited by phenothiazines [9], putative calmodulin 'antagonists' which exert numerous effects including inhibition of protein kinase C [lo]. The mechanisms underlying extrusion of platelet Ca2+ are less well characterised.…”

Section: Introductionmentioning

confidence: 99%

Regulation of platelet cytosolic free calcium by cyclic nucleotides and protein kinase C

1985

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PAF elicits a rapid, concentration-dependent elevation of platelet cytosolic free calcium ([Car]), measured by quin2. Elevation of [Car] is transient, and the rate of reversal increases with agonist concentration. Adenylate cyclase stimulants (PGI,, PGDJ and 8-bromo CAMP; a guanylate cyclase stimulant (sodium nitroprusside) and 8-bromo cGMP; and a protein kinase C stimulant (phorbol myristate acetate) block the elevation of [Car] induced by PAF, and accelerate its reversal. These results suggest that CAMP, cGMP and 1,2-diacylglycerol (DAG) could act as second messengers to regulate [Car] in platelets. As PAF is known to stimulate platelet phosphoinositide hydrolysis (ergo DAG formation) but fails to elevate platelet CAMP or cGMP. it is proposed that DAG, via activation of protein kinase C, may act as an endogenous modulator of platelet [Car]: an action that contributes to the role of DAG as a bi-directional regulator of platelet reactivity.

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Relationship between structure of phenothiazine analogues and their activity on platelet calcium fluxes

Cited by 24 publications

References 31 publications

Correlated expression of the 97 kDa sarcoendoplasmic reticulum Ca2+-ATPase and Rap1B in platelets and various cell lines

Correlated expression of the 97 kDa sarcoendoplasmic reticulum Ca2+-ATPase and Rap1B in platelets and various cell lines

The phosphoprotein that regulates platelet Ca2+ transport is located on the plasma membrane, controls membrane-associated Ca2+-ATPase and is not glycoprotein Ib β-subunit

Regulation of platelet cytosolic free calcium by cyclic nucleotides and protein kinase C

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