Biomedical subjects

F Wuytack

Publications and source records attributed to F Wuytack.

At least 91 records · Page 5Linked to original sources

PubMed1991

[The Ca(2+)-transport ATPases of smooth muscle].

The cytoplasmic Ca2+ concentration plays a central role in the contraction of smooth muscle cells. The concentration of cytoplasmic Ca2+ is determined for an important part by the operation of Ca(2+)-transport ATPases which extrude Ca2+ from the cell or accumulate the ion in the endoplasmic reticulum. The present work concerns the characterization of the Ca(2+)-transport ATPases of smooth muscle by biochemical, immunochemical and recombinant DNA techniques. This study also includes the investigation of the regulation of the Ca(2+)-transport ATPases and of the expression of associated Ca(2+)-binding proteins. Methods were developed for the purification of endoplasmic reticulum and plasma membranes from smooth-muscle cells. From the study of the phosphorylated transport intermediates and the proteolytic breakdown products, and by using polyclonal and monoclonal antibodies we could conclude that two different Ca(2+)-transport ATPases are expressed in smooth-muscle cells. Of each of these types of Ca(2+)-transport ATPases different isoforms exist. These isoforms were further characterized at the cDNA level and by generating isoform-specific antibodies. One isoform of the plasma-membrane Ca(2+)-pump and two different organellar-type Ca(2+)-pumps have been cloned and sequenced. In smooth-muscle cells, the primary RNA transcripts of the gene of the SERCA2 Ca(2+)-transport ATPase are alternatively processed in three different ways. In neural tissues even a fourth mode of splicing occurs. These different splice modes can be explained by the analysis of the exon/intron structure of the SERCA2 gene. The regulation of the alternative RNA splicing was studied on the stable muscle-cell line BC3H1 during induced myogenic differentiation. From this study we could conclude that the mechanisms responsible for active Ca(2+)-transport in smooth-muscle cells partially resemble those of non-muscle cells, and partially resemble the corresponding system in cardiac cells, but not those in skeletal muscle. A similar conclusion was reached concerning the regulation of the Ca(2+)-transport ATPase of the endoplasmic reticulum via the phosphorylation of phospholamban, and for the expression of the Ca(2+)-binding protein calsequestrin.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

A study of the organellar Ca2(+)-transport ATPase isozymes in pig cerebellar Purkinje neurons.

Pig cerebellar Purkinje neurons express a high level of Ca2(+)-transport ATPases in their intracellular Ca2+ stores. This was shown at the mRNA level by Northern blotting and in situ hybridization and at the protein level by Western blotting and immunocytochemistry. The majority of the Ca2(+)-transport ATPases in these neurons belongs to the SERCA2b type (i.e., the Ca2(+)-pump isoform found in most nonmuscle cells). The SERCA2a (cardiac/slow-twitch skeletal/smooth muscle) Ca2(+)-pump isoform is expressed only at very low levels. The main Ca2(+)-pump messenger is 6.0 kilobases long and belongs to a class 4-type processing of SERCA2, which is exclusively confined to the cerebrum and cerebellum. Phospholamban, a regulator of the SERCA2 Ca2(+)-transport ATPase in cardiac/slow-twitch skeletal/smooth muscle, could not be detected in Purkinje neurons.

Animals↗

PubMed1990

Expression of endoplasmic-reticulum Ca2(+)-pump isoforms and of phospholamban in pig smooth-muscle tissues.

The expression of the gene 2 sarcoplasmic/endoplasmic-reticulum Ca2(+)-pump isoforms (SERCA2a and SERCA2b) and of phospholamban was studied in pig smooth muscle of the stomach, longitudinal ileum, pulmonary artery and aorta. mRNA levels were determined using an RNAase protection assay. The SERCA2 isoforms and phospholamban were tested on Western blots with a panel of antibodies, some of which were isoform-specific. The pig smooth-muscle tissues all contained comparable SERCA2 mRNA levels, but these levels were 10-20-fold lower than SERCA2 mRNA levels in cardiac muscle. Of the SERCA2 mRNAs in smooth muscle, 72-81% encoded the non-muscle isoform (SERCA2b), and Western blot analysis with isoform-specific antibodies confirmed that the SERCA2b isoform is the predominant endoplasmic-reticulum Ca2(+)-pump in smooth muscle. In contrast with SERCA2 mRNA levels, phospholamban mRNA levels varied by 12-fold between the different pig smooth-muscle tissues, with low and very low levels in the pig pulmonary artery and the pig aorta respectively. The differential expression of phospholamban was also confirmed on Western blots. The finding that the phospholamban content varied between the different smooth-muscle tissues whereas the SERCA2 expression remained rather constant indicates that, in pig smooth muscle, the expression of phospholamban is not coupled with that of SERCA2.

Animals↗

PubMed1990

Molecular cloning and sequencing of the plasma-membrane Ca2+ pump of pig smooth muscle.

cDNAs coding for the plasma-membrane Ca2+ pump have been isolated from a pig smooth-muscle cDNA library and sequenced. The open reading frame encodes a protein of 1220 amino acids, which corresponds to the one already described in a human teratoma cell line. We demonstrate here that this cDNA probably represents the only isoform of the plasma-membrane Ca2(+)-transport ATPase expressed in this smooth muscle. There is no evidence for the expression of any other plasma-membrane Ca2(+)-pump gene, or for the presence of other alternatively spliced isoforms. These results are in apparent contradiction to those obtained on protein levels which demonstrate the reaction of at least two different polypeptides with a panel of antibodies against the plasma-membrane ATPase. It is suggested that these two polypeptides could result from a post-translational modification of one single enzyme.

Amino Acid Sequence↗

PubMed1990

Ruthenium red and compound 48/80 inhibit the smooth-muscle plasma-membrane Ca2+ pump via interaction with associated polyphosphoinositides.

We will demonstrate the compound 48/80 and ruthenium red inhibit the smooth-muscle plasma-membrane Ca2+ pump by counteracting the stimulant effect of negatively charged phospholipids. Both substances did not affect the purified enzyme re-activated by pure phosphatidylcholine or phosphatidylinositol and measured in the absence of calmodulin, indicating that under these conditions they did not have a direct effect on the ATPase protein. Ruthenium red and compound 48/80 however inhibited the (Ca2(+) + Mg2+)-ATPase in the presence of phosphatidylinositol 4-phosphate and especially phosphatidylinositol 4,5-bisphosphate. The K0.5 for inhibition was 25 microM ruthenium red and 9 micrograms/ml of compound 48/80. The inhibition by ruthenium red developed slowly with half maximal inhibition occurring after about 75 s while that by compound 48/80 developed immediately within the time required for mixing. The efficacy of ruthenium red increased as the concentration of the acidic phospholipid increased, while no such cooperativity was observed for compound 48/80. Ruthenium red reduced the Vmax for Ca2+ without affecting the affinity for Ca2+, while compound 48/80 decreased both parameters. In conclusion, although ruthenium red and compound 48/80 affect the ATPase differently, both substances most likely inhibit the plasma-membrane Ca2+ pumping by counteracting the stimulation by negatively charged phospholipids.

Animals↗

PubMed1990

Characterization of the mRNAs encoding the gene 2 sarcoplasmic/endoplasmic-reticulum Ca2+ pump in pig smooth muscle.

The gene 2 sarcoplasmic/endoplasmic-reticulum (SR/ER) Ca2+ pump is expressed in slow skeletal and cardiac muscle, smooth muscle and non-muscle tissues. We have analysed the gene 2 Ca2+ pump mRNAs using a panel of anti-sense RNA probes which recognize either the muscle (class 1) or the non-muscle (class 2) transcript, or both. In pig smooth muscle, we confirmed the presence of the class 1 and class 2 mRNAs of 4.4 kb length and we also detected a third mRNA of 8.0 kb which reacted with both the class 1 and class 2 riboprobes. A 4.2 kb cDNA corresponding to the 3' part of the 8.0 kb mRNA was cloned from a pig gastric smooth muscle cDNA library. Nucleotide sequence analysis of this clone revealed that the 8.0 kb mRNA (class 3 transcript) contained both the non-muscle-specific and the muscle-specific exons separated by a 2.4 kb intron which has not been removed. The class 3-mRNA-encoded SR/ER Ca2+ pump is identical to the class 2-encoded non-muscle isoform. Northern blot analysis demonstrated that, in cardiac muscle, the class 1 mRNA (encoding the muscle isoform) is the predominant messenger, whereas in non-muscle tissues the class 2 and 3 mRNAs (encoding the non-muscle isoform) predominate. In smooth muscle all three mRNA types are present. The tissue distribution of the mRNA types suggests a tissue-dependent processing of the primary transcript of the sarcoplasmic/endoplasmic reticulum Ca2+ pump gene 2.

Animals↗

PubMed1990

Effects of cyclic nucleotide dependent protein kinases on the endoplasmic reticulum Ca2+ pump of bovine pulmonary artery.

This paper describes the stimulation by cyclic nucleotide dependent protein kinases on the Ca2+ uptake by isolated endoplasmic reticulum (ER) vesicles from the bovine main pulmonary artery. This ER fraction has previously been shown to be highly enriched in phospholamban, a protein kinase substrate that has been well characterized in cardiac sarcoplasmic reticulum (SR), where its phosphorylation is accompanied by an increased rate of Ca2+ uptake. As previously observed for the phosphorylation of phospholamban, the stimulation of the rate of Ca uptake was as high with cGMP dependent protein kinase as with cAMP dependent protein kinase. The effect of phosphorylation of the ER membranes from smooth muscle on the Ca2+ uptake was smaller than that seen in cardiac SR, and it was only observed if albumin was included during the isolation of the membranes. This relatively small effect is probably not due to a lower ratio of phospholamban to Ca2(+)-transport enzyme in the ER membranes as compared to cardiac SR. Several alternative explanations are discussed.

Albumins↗

PubMed1989

Antibodies against the non-muscle isoform of the endoplasmic reticulum Ca2(+)-transport ATPase.

We report here the production of a polyclonal antiserum which specifically recognizes an epitope confined to the ultimate 12-residue-long C-terminus of an alternatively spliced transcript of gene 2 encoding the sarcoplasmic reticulum Ca2+ pump in slow skeletal and cardiac muscle. This alternatively spliced transcript was shown to be mainly represented in non-muscle tissues. These antibodies have enabled us to show the presence of the unique C-terminus of this type of Ca2+ pump, as predicted from the cDNA sequence, in the endoplasmic reticulum of vascular and gastric smooth muscle, liver and kidney.

Amino Acid Sequence↗

PubMed1989

Role of arginine residues in the stimulation of the smooth-muscle plasma-membrane Ca2+ pump by negatively charged phospholipids.

Negatively charged phospholipids strongly stimulate the purified plasma membrane Ca2+ pump of erythrocytes [Enyedi, Flura, Sarkadi, Gardos & Carafoli (1987) J. Biol. Chem. 262, 6425-6430] and of smooth muscle [Missiaen, Raeymaekers, Wuytack, Vrolix, De Smedt & Casteels, (1989) Biochem. J. 263, 687-694]. We have investigated the role of arginine residues in the interaction of these acidic phospholipids with the smooth-muscle Ca2+ transport ATPase. The arginine-modifying reagent phenylglyoxal inhiibited the ATPase activity in a time-dependent fashion by decreasing the Vmax. of the Ca2(+)-activation curve. Low concentrations of PtdIns, PtdIns4P, PtdIns(4,5) P2, phosphatidylserine and phosphatidic acid partially prevented this inactivation. This protective effect was however not apparent at higher concentrations of PtdIns4P, PtdIns(4,5) P2 and phosphatidic acid, which may be related to the previously observed inhibition of the enzyme at higher concentrations of these phospholipids. These findings indicate that the functionally important interaction of the acidic lipids with the protein occurs at least partially via arginine residue(s).

Aldehydes↗

PubMed1989

Phospholipid-protein interactions of the plasma-membrane Ca2+-transporting ATPase. Evidence for a tissue-dependent functional difference.

The aim of the present work was to investigate the stimulation of the plasma-membrane Ca2+-transporting ATPase by negatively charged phospholipids. The Ca2+-transporting ATPase was purified from pig stomach smooth muscle and from pig erythrocytes, and was reactivated with phosphatidylcholine (PC) in the presence and absence of negatively charged phospholipids. The substitution of phosphatidylinositol (PI), phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol 4,5-bisphosphate (PIP2), phosphatidic acid (PA) or phosphatidylserine (PS) for PC induced profound changes in the Vmax, the K0.5 and the Hill coefficient of the Ca2+-activation curves for both ATPases. Low concentrations of each of the negatively charged phospholipids increased the Vmax., but high ratios of PIP, PIP2 or PA to PC decreased this parameter. PI, PA and PS increased the Vmax. of the erythrocyte enzyme to a larger extent than that of the smooth-muscle enzyme. This difference was less pronounced for PIP and absent for PIP2. PI (greater than 20% PC substituted), PIP, PIP2, PA and PS all increased the affinity of the two Ca2+-transporting ATPases for Ca2+ in the following order of potency: PIP2 greater than PIP greater than PI approximately PS approximately PA. PI, PA and PS increased the Ca2+ affinity of the smooth-muscle enzyme more than that of the erythrocyte enzyme; this difference was less pronounced for PIP and absent for PIP2. Even in the presence of calmodulin, all of the negatively charged phospholipids were still able to increase the Vmax. of the erythrocyte enzyme, whereas only PIP and PIP2 increased the affinity for Ca2+. The effect of PI at low concentrations (less than 20%) on the erythrocyte enzyme was peculiar in that it caused a decrease in the Ca2+ affinity instead of an increase. This effect was not observed for the smooth-muscle enzyme. All of the negatively charged phospholipids slightly increased the Hill coefficient for Ca2+ of both ATPases, and this effect was additive to that of calmodulin. The stimulation of the erythrocyte enzyme exhibited positive co-operativity towards PI and PIP, whereas that of the smooth-muscle enzyme did not. It is concluded (1) that there is a correlation between the number of negative charges on the phospholipids (PIP2 greater than PIP greater than PA approximately PI approximately PS) and the magnitude of their effect on the Vmax. and the K0.5 for Ca2+, and (2) that the action of the lipids on the smooth-muscle enzyme differs from that on the erythrocyte enzyme, indicating that these two Ca2+-transporting ATPases are not the same.

Animals↗

PubMed1989

cDNA cloning and sequencing of phospholamban from pig stomach smooth muscle.

Phospholamban cDNA from pig stomach smooth muscle was cloned and sequenced. The 737-nucleotide-residue cDNA contained an open reading frame of 156 nucleotide residues encoding a peptide of 52 amino acid residues (Mr 6080). This peptide shares 100% sequence identity with dog cardiac-muscle phospholamban. It differs from rabbit cardiac-muscle and slow-twitch skeletal-muscle phospholamban only at position 2, which is a glutamic acid residue in rabbit phospholamban, but an aspartic acid residue in the pig smooth-muscle protein. Northern-blot analysis reveals the presence of several phospholamban mRNAs in smooth muscle, but a 900-nucleotide-residue and a 2800-nucleotide-residue transcript predominate.

Adenosine Triphosphatases↗

PubMed1989

Alkalinization stimulates the purified plasma-membrane Ca2+ pump by increasing its Ca2+ affinity.

The finding that negatively charged phospholipids activate the plasma-membrane (Ca2+ + Mg2+)-ATPase and that polycations counteract this stimulation suggest that negative charges in the environment of the ATPase protein could be important for its function. The aim of the present work was to investigate whether changing the charges on the ATPase protein itself by modifying the pH within the physiological range affects the activity of the purified plasma-membrane Ca2+ pump from stomach smooth muscle. Increasing the pH from 6.9 to 7.4 and using 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid (BAPTA) as a Ca2+ buffer, doubled the ATPase activity at 0.3 microM-Ca2+ in the presence of 100% phosphatidylcholine (PC) or after substituting 20% of the PC by negatively charged phospholipids PtdIns, PtdIns4P, phosphatidylserine and phosphatidic acid. This stimulatory effect was due to an increased affinity of the enzyme for Ca2+, while the Vmax. remained unaffected. In the case of PtdIns(4,5)P2, a stimulatory effect upon alkalinization was only observed at a PtdIns(4,5)P2 concentration of 10%. When a concentration of 20% was used, alkalinization decreased the Vmax. and no stimulatory effect on the ATPase at 0.3 microM-Ca2+ could be observed. Alkalinization not only stimulated the purified Ca2+ pump, but it also increased the activity of the enzyme in a plasma-membrane-enriched fraction from stomach smooth muscle by a factor of 2.06. The ionophore A23187-induced Ca2+ uptake in closed inside-out vesicles also increased by a factor of 2.54 if the pH was changed from 6.9 to 7.4. This finding indicates that the effect of pH is most likely to be exerted at the cytoplasmic site of the Ca2+ pump protein.

Animals↗

PubMed1989

Polyamines and neomycin inhibit the purified plasma-membrane Ca2+ pump by interacting with associated polyphosphoinositides.

We investigated the effect of spermine, spermidine, putrescine and neomycin on the activity of the plasma-membrane Ca2+ pump and on its stimulation by negatively charged phospholipids and calmodulin. Millimolar concentrations of spermine and to a lesser extent of spermidine decreased the ATPase activity in the presence of phosphatidylinositol 4,5-bisphosphate (PIP2), without affecting the stimulation by phosphatidylinositol 4-phosphate (PIP). Sub-millimolar concentrations of neomycin inhibited the stimulation of the ATPase by PIP and by PIP2. Neomycin was more effective at the higher concentrations of PIP and PIP2. We discuss that these findings are compatible with the hypothesis that PIP and PIP2 bind to the ATPase and that several of these molecules have to be available to stimulate the ATPase.

Animals↗

PubMed1989

AIF4-induced inhibition of the ATPase activity, the Ca2+-transport activity and the phosphoprotein-intermediate formation of plasma-membrane and endo(sarco)plasmic-reticulum Ca2+-transport ATPases in different tissues. Evidence for a tissue-dependent functional difference.

AIF4- inhibits the (Ca2+ + Mg2+)-ATPase activity of the plasma-membrane and the sarcoplasmic-reticulum Ca2+-transport ATPase [Missiaen, Wuytack, De Smedt, Vrolix & Casteels (1988) Biochem. J. 253, 827-833]. The aim of the present work was to investigate this inhibition further. We now report that AIF4- inhibits not only the (Ca2+ + Mg2+)-ATPase activity, but also the ATP-dependent 45Ca2+ transport, and the formation of the phosphoprotein intermediate by these pumps. Mg2+ potentiated the effect of AIF4-, whereas K+ had no such effect. The plasma-membrane Ca2+-transport ATPase from erythrocytes was 20 times less sensitive to inhibition by AIF4- as compared with the Ca2+-transport ATPase from smooth muscle. The endoplasmic-reticulum Ca2+-transport ATPase from smooth muscle was inhibited to a greater extent than the sarcoplasmic-reticulum Ca2+-transport ATPase of slow and fast skeletal muscle.

Adenosine Triphosphatases↗

PubMed1989

Evidence for two isoforms of the endoplasmic-reticulum Ca2+ pump in pig smooth muscle.

cDNA clones coding for the endoplasmic reticulum Ca2+-transport ATPase have been cloned from a pig smooth-muscle cDNA library. The transcripts can be divided into two classes which differ in their 3' ends due to alternative splicing of the primary gene transcript. The class 1 cDNA encodes a protein of 997 amino acids (Mr 110,000). The class 2 protein (1042 amino acids; Mr 115,000) is completely identical to the class 1 protein except that the four C-terminal amino acids of the class 1 protein are replaced in the class 2 protein with a tail of 49 amino acids. Comparison of these sequences with other Ca2+ pump sequences reveals that the class 1 isoform corresponds to the sarcoplasmic reticulum Ca2+ pump of slow-twitch skeletal/cardiac muscle, whereas the class 2 protein corresponds to a Ca2+ pump recently detected in non-muscle tissues.

Amino Acid Sequence↗

PubMed1989

Measurement of microsomal ATPase activities: a comparison between the inorganic phosphate-release assay and the NADH-coupled enzyme assay.

The specific activity of the Mg2+-ATPase and the (Ca2+ + Mg2+)-ATPase has been measured in a microsomal fraction from pig antral smooth muscle with the phosphate-release assay and the NADH-coupled enzyme assay, and the release of inorganic phosphate as a function of time is compared with the concomitant production of ADP. Both assays are found to overestimate the true Mg2+-ATPase activity. The adenylate kinase inhibitor P1,P5-di(adenosine-5'-)pentaphosphate (Ap5A) reduces the specific activity of the Mg2+-ATPase measured in the NADH-coupled enzyme assay to about half of its original value; however, it does not affect the specific activity of the Mg2+-ATPase in the Pi-release assay. The considerable overestimation of the Mg2+-ATPase activity in the NADH-coupled enzyme assay results from a combined action of an ATP pyrophosphatase (ATP in equilibrium AMP + PPi) and adenylate kinase activity contaminating the microsomes. The adenylate kinase activity in the microsomes catalyses the conversion of AMP formed by the ATP pyrophosphatase together with ATP into two ADP's. Also the phosphate-release assay is prone to an overestimation artefact because an inorganic pyrophosphatase will degrade the pyrophosphate and thus lead to additional Pi-production. Measurements of AMP and NAD+ production by HPLC confirmed our proposed reaction scheme. The same (Ca2+ + Mg2+)-ATPase activity is found in both assays, because the (Ca2+ + Mg2+)-ATPase activity is calculated from the difference in ATPase activity in the presence and absence of Ca2+, so that as a consequence the interfering activities are automatically subtracted.

Adenosine Diphosphate↗

PubMed1989

Smooth muscle expresses a cardiac/slow muscle isoform of the Ca2+-transport ATPase in its endoplasmic reticulum.

Smooth muscle expresses in its endoplasmic reticulum an isoform of the Ca2+-transport ATPase that is very similar to or identical with that of the cardiac-muscle/slow-twitch skeletal-muscle form. However, this enzyme differs from that found in fast-twitch skeletal muscle. This conclusion is based on two independent sets of observations, namely immunological observations and phosphorylation experiments. Immunoblot experiments show that two different antibody preparations against the Ca2+-transport ATPase of cardiac-muscle sarcoplasmic reticulum also recognize the endoplasmic-reticulum/sarcoplasmic-reticulum enzyme of the smooth muscle and the slow-twitch skeletal muscle whereas they bind very weakly or not at all to the sarcoplasmic-reticulum Ca2+-transport ATPase of the fast-twitch skeletal muscle. Conversely antibodies directed against the fast-twitch skeletal-muscle isoform of the sarcoplasmic-reticulum Ca2+-transport ATPase do not bind to the cardiac-muscle, smooth-muscle or slow-twitch skeletal-muscle enzymes. The phosphorylated tryptic fragments A and A1 of the sarcoplasmic-reticulum Ca2+-transport ATPases have the same apparent Mr values in cardiac muscle, slow-twitch skeletal muscle and smooth muscle, whereas the corresponding fragments in fast-twitch skeletal muscle have lower apparent Mr values. This analytical procedure is a new and easy technique for discrimination between the isoforms of endoplasmic-reticulum/sarcoplasmic-reticulum Ca2+-transport ATPases.

Animals↗

PubMed1989

AlF-4 inhibits the accumulation of Ca in the endoplasmic reticulum in intact myometrial strips, but not in the rabbit ear artery.

AlF-4, known to be a potent modulator of G-proteins, also inhibits purified "P"-type cation-transport ATPases (Missiaen et al. 1988). The aim of the present work is to find out whether AlF-4 also inhibits these ATPases in intact cells. We therefore have studied the effect of AlF-4 on the force development and on 45Ca2+ -fluxes of muscle strips from rat myometrium and rabbit ear artery. 1 mM-NaF plus 10 microM-AlCl3 induces in both tissues a tonic contraction that is completely blocked by 0.5 mM-deferoxamine. The contractile response in myometrium exceeds that of the ear artery. These contractions are independent of an activation of G-proteins but their amplitude depends on [Ca2+]o. Application of AlF-4 during the loading of the endoplasmic reticulum of myometrium with Ca2+ dramatically reduces the amount of stored Ca2+ as estimated from its release induced by 1 mM-carbachol during incubation in Ca-free solution. This effect could be due to a predominant inhibitory effect of AlF-4 on the (Ca2+ + Mg2+)-ATPase of the endoplasmic reticulum. Such effect could not be established in rabbit ear artery. The increase of the fractional loss of 45Ca2+ induced by 10 microM-norepinephrine in rabbit ear artery is not inhibited by AlF-4. It is concluded that the inhibition of the endoplasmic-reticulum (Ca2+ + Mg2+)-ATPase in intact myometrial cells warns us against explaining all effects of AlF-4 on intact cells only by an activation of G-proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum↗