Biomedical subjects

A Yatani

Publications and source records attributed to A Yatani.

At least 37 records · Page 2Linked to original sources

PubMed1999

ACE inhibition improves cardiac NE uptake and attenuates sympathetic nerve terminal abnormalities in heart failure.

Cardiac sympathetic nerve terminal dysfunction plays an important role in the downregulation of myocardial beta-adrenoceptors in heart failure. To determine whether chronic angiotensin-converting enzyme (ACE) inhibition improved cardiac sympathetic nerve terminal function and hence increased myocardial beta-adrenergic responsiveness, we administered ACE inhibitors to dogs with chronic right-sided heart failure (RHF) produced by tricuspid avulsion and pulmonary artery constriction. The RHF animals exhibited fluid retention, elevated right heart filling pressures, blunted inotropic response to isoproterenol, and reduced beta-adrenoceptor density. These changes were accompanied by decreases in right ventricular norepinephrine (NE) uptake and neuronal NE histofluorescence and tyrosine hydroxylase immunoreactive profiles. ACE inhibitors had no effect on the production of heart failure but greatly reduced the attenuation of cardiac NE uptake, neuronal NE histofluorescence, and tyrosine hydroxylase immunoreactive profiles. ACE inhibition also improved the inotropic response to isoproterenol and restored myocardial beta-adrenoceptor density. The changes probably are caused by reduction of cardiac NE release by ACE inhibition and may contribute to the beneficial effects of ACE inhibitor therapy in patients with chronic heart failure.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1999

Differential regulation of inotropy and lusitropy in overexpressed Gsalpha myocytes through cAMP and Ca2+ channel pathways.

We investigated the mechanisms responsible for altered contractile and relaxation function in overexpressed Gsalpha myocytes. Although baseline contractile function (percent contraction) in Gsalpha mice was similar to that of wild-type (WT) mice, left ventricular myocyte contraction, fura-2 Ca2+transients, and Ca2+ channel currents (ICa) were greater in Gsalpha mice in response to 10(-8) M isoproterenol (ISO) compared with WT mice. The late phase of relaxation of the isolated myocytes and fura-2 Ca2+ transients was accelerated at baseline in Gsalpha but did not increase further with ISO. In vivo measurements using echocardiography also demonstrated enhanced relaxation at baseline in Gsalpha mice. Forskolin and CaCl2 increased contraction similarly in WT and Gsalpha mice. Rp-cAMP, an inhibitor of protein kinase, blocked the increases in contractile response and Ca2+ currents to ISO in WT and to forskolin in both WT and Gsalpha. It also blocked the accelerated relaxation in Gsalpha at baseline but not the contractile response to ISO in Gsalpha myocytes. Baseline measurements of cAMP and phospholambation phosphorylation were enhanced in Gsalpha compared with WT. These data indicate that overexpression of Gsalpha accelerates relaxation at end diastolic but does not affect baseline systolic function in isolated myocytes. However, the enhanced responses to sympathetic stimulation partly reflect increased Ca2+ channel activity; i.e the cellular mechanisms mediating these effects appear to involve a cAMP-independent as well as a cAMP-dependent pathway.

Animals↗

PubMed1998

Cardiac-specific overexpression of mouse cardiac calsequestrin is associated with depressed cardiovascular function and hypertrophy in transgenic mice.

Calsequestrin is a high capacity Ca2+-binding protein in the sarcoplasmic reticulum (SR) lumen. To elucidate the functional role of calsequestrin in vivo, transgenic mice were generated that overexpressed mouse cardiac calsequestrin in the heart. Overexpression (20-fold) of calsequestrin was associated with cardiac hypertrophy and induction of a fetal gene expression program. Isolated transgenic cardiomyocytes exhibited diminished shortening fraction (46%), shortening rate (60%), and relengthening rate (60%). The Ca2+ transient amplitude was also depressed (45%), although the SR Ca2+ storage capacity was augmented, as suggested by caffeine application studies. These alterations were associated with a decrease in L-type Ca2+ current density and prolongation of this channel's inactivation kinetics without changes in Na+-Ca2+ exchanger current density. Furthermore, there were increases in protein levels of SR Ca2+-ATPase, phospholamban, and calreticulin and decreases in FKBP12, without alterations in ryanodine receptor, junctin, and triadin levels in transgenic hearts. Left ventricular function analysis in Langendorff perfused hearts and closed-chest anesthetized mice also indicated depressed rates of contraction and relaxation of transgenic hearts. These findings suggest that calsequestrin overexpression is associated with increases in SR Ca2+ capacity, but decreases in Ca2+-induced SR Ca2+ release, leading to depressed contractility in the mammalian heart.

Amino Acid Sequence↗

PubMed1998

Four conductance levels of cloned cardiac L-type Ca2+ channel alpha1 and alpha1/beta subunits.

Formation of single channel subconductance is one of the unique characteristics of the L-type Ca2+ channel. Although alpha1 subunit exhibits a primary function of the channel, it remains uncertain whether alpha1 subunit alone is able to produce subconductance. We tested this by studying single channel currents of cloned cardiac alpha1 subunit expressed in Chinese hamster fibroblast cells, with/without coexpression of cardiac beta subunit. The alpha1 subunit exhibited four distinct levels of conductance (22.7, 14.3, 6.2 and 3.2 pS). Coexpression of beta subunit significantly increased the number of openings in all four levels of conductance without changing the conductance values.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1998

Altered sarcoplasmic reticulum Ca2+ ATPase gene expression in congestive heart failure: effect of chronic norepinephrine infusion.

We have examined the ryanodine receptor, Ca(2+)-ATPase, calsequestrin and phospholamban mRNA levels in the left ventricles of pacing-induced heart failure and norepinephrine infusion dogs. The heart failure dogs showed a decrease in the levels of ryanodine receptor and Ca(2+)-ATPase mRNAs. Norepinephrine infusion caused a reduction of Ca(2+)-ATPase mRNA but no change in ryanodine receptor mRNA. There was a corresponding reduction of the immunoreactive Ca(2+)-ATPase protein levels in both heart failure and norepinephrine infusion animals compared to controls. In contrast, the mRNAs of calsequestrin and phospholamban were unchanged in dogs with either congestive heart failure or norepinephrine infusion. Thus, since norepinephrine infusion and congestive heart failure produced similar reductions of Ca(2+)-ATPase mRNA and protein, we postulate that the down-regulation of Ca(2+)-ATPase in congestive heart failure may be caused, at least in part, by sympathetic stimulation that occurs in heart failure.

Animals↗

PubMed1998

Overexpression of phospholamban alters inactivation kinetics of L-type Ca2+ channel currents in mouse atrial myocytes.

In mammalian ventricular myocytes, inactivation of L-type Ca2+ channels (CaCh) is controlled by voltage- and Ca2+-dependent mechanisms. The Ca2+-dependent component is regulated by the Ca2+ released from the sarcoplasmic reticulum (SR). However, little is known about the inactivation properties of CaCh in atrial myocytes, which lack spatial coupling between CaCh and SR Ca2+ release channels. The cardiac SR Ca2+ load is determined by the activity of SR Ca2+-ATPase, which is inversely regulated by the levels of phospholamban (PLB). To investigate the role of SR Ca2+ in atrial myocytes, Ca2+ currents (I Ca) were recorded in mouse atrial myocytes recorded from wild-type (WT) mice and the characteristics were compared to those obtained from atrial myocytes from the transgenic mice overexpressing PLB (PLB-OEX). ICa from WT exhibited fast and slow components of inactivation and the rate of inactivation was slowed when SR Ca2+ was depleted by caffeine, suggesting that the inactivation of atrial ICa is modulated by SR Ca2+ load. The current density and voltage-dependence of ICa were similar between the two groups. However, the fast component of inactivation was significantly reduced in PLB-OEX. When Ca2+ was replaced by Ba2+ or in the presence of caffeine, inactivation was slowed and the decay of the current was not significantly different between WT and PLB-OEX. These results suggest that the inactivation of ICa in mouse atrial myocytes involves Ca2+-dependent and voltage-dependent components. The decrease in the faster component of inactivation in PLB-OEX is consistent with the idea that CaCh and SR Ca2+ release channels are functionally coupled and Ca2+ released from the SR contributes the Ca2+-dependent inactivation component.

Animals↗

PubMed1998

Ca2+ entry through cardiac L-type Ca2+ channels modulates beta-adrenergic stimulation in mouse ventricular myocytes.

beta-adrenergic receptor (beta-AR) stimulation increases cardiac L-type Ca2+ channel (CaCh) currents via cAMP-dependent phosphorylation. We report here that the affinity and maximum response of CaCh to isoproterenol (Iso), in mouse ventricular myocytes were significantly higher when Ba2+ was used as the charge carrier (IBa) instead of Ca2+ (ICa). The EC50 and maximum increase of peak currents were 43.7 +/- 7.9 nM and 1.8 +/- 0.1-fold for ICa and 23.3 +/- 4.7 nM and 2.4 +/- 0.1-fold for IBa. When cells were dialyzed with the faster Ca2+ chelator, BAPTA, both sensitivity and maximum response of ICa to Iso were significantly augmented compared to cells with EGTA (EC50 of 23.1 +/- 5.2 nM and maximal increase of 2.2 +/- 0.1-fold). Response of ICa to forskolin was also significantly increased when cells were dialyzed with BAPTA or when currents were measured in Ba2+. In contrast, depletion of the sarcoplasmic reticulum (SR) Ca2+ stores by ryanodine did not alter sensitivity of ICa to Iso or forskolin. These results suggest that the Ca2+ entering through CaCh regulates cAMP-dependent phosphorylation, and such negative feedback may play a significant role in cellular Ca2+ homeostasis and contraction in cardiac cells during beta-AR stimulation.

Adrenergic beta-Agonists↗

PubMed1997

cAMP-dependent regulation of cardiac L-type Ca2+ channels requires membrane targeting of PKA and phosphorylation of channel subunits.

The cardiac L-type Ca2+ channel is a textbook example of an ion channel regulated by protein phosphorylation; however, the molecular events that underlie its regulation remain unknown. Here, we report that in transiently transfected HEK293 cells expressing L-type channels, elevations in cAMP resulted in phosphorylation of the alpha1C and beta2a channel subunits and increases in channel activity. Channel phosphorylation and regulation were facilitated by submembrane targeting of protein kinase A (PKA), through association with an A-kinase anchoring protein called AKAP79. In transfected cells expressing a mutant AKAP79 that is unable to bind PKA, phosphorylation of the alpha1C subunit and regulation of channel activity were not observed. Furthermore, we have demonstrated that the association of an AKAP with PKA was required for beta-adrenergic receptor-mediated regulation of L-type channels in native cardiac myocytes, illustrating that the events observed in the heterologous expression system reflect those occurring in the native system. Mutation of Ser1928 to alanine in the C-terminus of the alpha1C subunit resulted in a complete loss of cAMP-mediated phosphorylation and a loss of channel regulation. Thus, the PKA-mediated regulation of L-type Ca2+ channels is critically dependent on a functional AKAP and phosphorylation of the alpha1C subunit at Ser1928.

Animals↗

PubMed1997

Charged amino acids near the pore entrance influence ion-conduction of a human L-type cardiac calcium channel.

Voltage-dependent L-type Ca2+ channels form highly selective pores for Ca2+ ions in the membranes of excitable cells. We investigated the functional role of negatively charged residues, within or near the selectivity region, in ion permeation of a human cardiac L-type Ca2+ channel. Glutamates in each of the four repeats, and an aspartate in repeat IV, were substituted with positively charged lysine. Wild-type and mutant Ca2+ channels were expressed in Xenopus oocytes. Block by Ca2+ and Mg2 of inward Li+ currents through the channels was used to assess the effects of amino acid substitutions on high-affinity divalent cation binding. The rank order of IC50's for Ca2+ block of I(Li) was: E677K > E1086K > E334K > E1387K > D1391K > or approximately wild-type. The order of IC50's for Mg2+ block of I(Li) indicated differential involvement of the same residues in Mg2+ binding: E 1387K > E334K > E1086K > E677K > D 1391K = wild-type. Mutants E1387K and D1391K effectively permeated Ba2+, but exhibited a decreased single-channel conductance. The unitary current amplitude carried by Na+, in the absence of external divalent cations, was slightly decreased in the E1387K mutant but not in the D1391K mutant. The results confirm that each of the four glutamates participate unequally in high-affinity Ca2+ binding. Additionally, our results indicate that these glutamate residues participate in Mg2+ binding. The glutamate at position 1387 may be only peripherally involved in the formation of a high-affinity Ca2+ -binding site but is central to a Mg2+ binding site accessible from the external side of the pore. The aspartate at position 1391 is most likely located just external to the selectivity region.

Amino Acid Sequence↗

PubMed1997

Modulation of cardiac Ca2+ channels by isoproterenol studied in transgenic mice with altered SR Ca2+ content.

Phospholamban (PLB) ablation is associated with enhanced sarcoplasmic reticulum (SR) Ca2+ uptake and attenuation of the cardiac contractile responses to beta-adrenergic agonists. In the present study, we compared the effects of isoproterenol (Iso) on the Ca2+ currents (ICa) of ventricular myocytes isolated from wild-type (WT) and PLB knockout (PLB-KO) mice. Current density and voltage dependence of ICa were similar between WT and PLB-KO cells. However, ICa recorded from PLB-KO myocytes had significantly faster decay kinetics. Iso increased ICa amplitude in both groups in a dose-dependent manner (50% effective concentration, 57.1 nM). Iso did not alter the rate of ICa inactivation in WT cells but significantly prolonged the rate of inactivation in PLB-KO cells. When Ba2+ was used as the charge carrier, Iso slowed the decay of the current in both WT and PLB-KO cells. Depletion of SR Ca2+ by ryanodine also slowed the rate of inactivation of ICa, and subsequent application of Iso further reduced the inactivation rate of both groups. These results suggest that enhanced Ca2+ release from the SR offsets the slowing effects of beta-adrenergic receptor stimulation on the rate of inactivation of ICa.

Adenosine Triphosphatases↗

PubMed1997

Chronic opiate-receptor inhibition in experimental congestive heart failure in dogs.

Acute administration of opiate-receptor antagonists has previously been shown to improve cardiac output aortic blood pressure, systolic ventricular performance, and the baroreflex function in conscious dogs with right-sided congestive heart failure (RHF). However, whether similar changes occur after chronic opiate-receptor inhibition in congestive heart failure is not known. To determine the chronic effects of opiate-receptor antagonism on RHF, we administered naltrexone (200 mg/day), a long-acting, orally active opiate-receptor blocking agent, to RHF and sham-operated animals for 6 wk. Naltrexone had no effects on resting heart rate, right atrial pressure, aortic pressure, or cardiac output in RHF dogs but increased the first derivative of right and left ventricular pressure with respect to time (dP/dt) at rest and improved the dP/dt response to isoproterenol. The inotropic responses to isoproterenol and forskolin in isolated right ventricular trabeculate muscle also were improved by chronic naltrexone in RHF. Myocardial beta-receptor density was reduced in the failing right ventricle compared with the control (58 +/- 3 vs. 108 +/- 6 fmol/mg protein, P < 0.01) but was unaffected by addition of naltrexone. Finally, naltrexone prevented the decline in baroreflex sensitivity that occurred in RHF (-0.2 +/- 0.5 vs. -6.0 +/- 0.5 ms/mmHg, P < 0.01). These effects of naltrexone did not occur in the shamoperated animals. Chronic opiate-receptor blockade with naltrexone attenuates the development of reduced adrenergic inotropic responsiveness and baroreflex subsensitivity that occur in RHF. Because there was a similar improvement in the forskolin response in the absence of significant alterations in myocardial beta-adrenoceptor density after naltrexone treatment, the improvement in adrenergically mediated inotropic effects probably is mediated via a postreceptor mechanism.

Animals↗

PubMed1997

Phospholamban deficiency alters inactivation kinetics of L-type Ca2+ channels in mouse ventricular myocytes.

Entry of Ca2+ through voltage-dependent L-type Ca2+ channels is critical for contraction in cardiac cells. In recent studies, cells from phospholamban (PLB) knockout (PLB-KO) mouse hearts showed significantly increased basal contractility with enhanced sarcoplasmic reticulum (SR) Ca2+ uptake. To test whether these effects of PLB ablation were associated with alterations of L-type Ca2+ channel function, we compared the properties of Ca2+ channel currents (I(Ca)) in ventricular myocytes isolated from wild-type (WT) and PLB-KO mouse hearts. L-type Ca2+ channels from mouse myocytes exhibited voltage-dependent gating and sensitivity to dihydropyridine drugs, similar to other mammalian species, and these properties were not altered by PLB ablation. I(Ca) from both WT and PLB-KO cells revealed two (fast and slow) components of inactivation kinetics. However, the proportion of the faster component was significantly larger in PLB-KO cells. Ryanodine (10 microM) reduced the rate of inactivation of I(Ca) for both WT and PLB-KO cells, but the reduction was more prominent in PLB-KO cells compared with WT cells. In contrast, the inactivation in a Ba2+ solution could be fitted by a single exponential similar to the slower component in Ca2+, and this was not altered in PLB-KO cells. The increase in the fast Ca2+-dependent inactivation component in PLB-KO cells supports the hypothesis that Ca2+ released from the SR regulates Ca2+ channel inactivation by affecting the levels of Ca2+ near the channel and suggests that this may be an important compensatory mechanism in the hyperdynamic PLB-KO heart.

Animals↗

PubMed1996

Amino acid substitutions in the rat Na+, K(+)-ATPase alpha 2-subunit alter the cation regulation of pump current expressed in HeLa cells.

1. To study the functional role of negatively charged amino acids (E327 and D925) located in the transmembrane region of the rat alpha 2-isoform of the Na+, K(+)-ATPase (rat alpha 2*) in ion transport, the effects of mutations on external K+ dependence and internal Na+ dependence of pump currents were assessed by the patch-clamp technique in combination with a system for rapid solution changes. 2. Amino acid residues were replaced by glutamine (E327Q) or leucine (D925L) and were introduced into rat alpha 2* cDNA which encodes a ouabain-resistant isoform. These mutant enzymes were stably expressed in HeLa cells. The endogenous ouabain-sensitive HeLa cell Na+, K(+)-ATPase activity was selectively inhibited by 1 microM ouabain present in both the growing media and the assay solution. 3. External K(+)- and internal Na(+)-dependent pump activation was observed in all cells expressing rat alpha 2*, E327Q or D925L; however, the apparent affinities were significantly reduced by the mutations. 4. In E327Q, the activation of pump current was slightly slower than for rat alpha 2*, whereas the deactivation rate was faster. In contrast, D925L produced pump current having dramatically slower activation and deactivation kinetics. 5. These results indicate that these negatively charged amino acids (E327 and D925) are important in cation-induced conformational changes of the protein, which are intermediate steps in the pump mechanism.

Amino Acid Sequence↗

PubMed1996

Elevated myocardial interstitial norepinephrine concentration contributes to the regulation of Na+,K(+)-ATPase in heart failure.

Myocardial Na+,K(+)-ATPase is reduced in congestive heart failure. To study the regulation of Na+,K(+)-ATPase in congestive heart failure, we performed Western and Northern blot analyses of ventricular myocardium of dogs with pacing-induced congestive heart failure and chronic norepinephrine infusion, using isoform-specific antibodies and cDNA probes. Congestive heart failure and norepinephrine infusion caused similar increases in myocardial interstitial norepinephrine concentration and reductions of myocardial Na+,K(+)-ATPase alpha 3-subunit protein, but differed in their effects on myocardial Na+,K(+)-ATPase alpha 3-subunit gene expression. Chronic norepinephrine infusion produced no changes in the steady-state mRNA level for the alpha 3-subunit of Na+,K(+)-ATPase, suggesting that the changes in Na+,K(+)-ATPase protein were induced via a post-transcriptional mechanism. In contrast, down-regulation of the Na+,K(+)-ATPase alpha 3-subunit in the failing heart was accompanied by a decreased alpha 3-subunit mRNA level, indicating the presence of a transcriptional event. The alpha 1-subunit protein content and mRNA level were not affected by either norepinephrine infusion or rapid ventricular pacing. We conclude that, while elevated myocardial interstitial norepinephrine levels may contribute substantially to the down-regulation of the Na+,K(+)-ATPase alpha 3-subunit in the failing myocardium, additional regulatory factors are responsible for the decreased myocardial alpha 3-subunit mRNA expression in congestive heart failure.

Animals↗

PubMed1996

Comparative studies of thrombolysis with single-chain and two-chain recombinant tissue-type plasminogen activators in canine coronary thrombosis.

Tissue-type plasminogen activator (t-PA) can occur in two different forms, single- and two-chain t-PA. Such a difference in structure of the t-PA molecule may induce different biological functions. We compared the thrombolytic efficacy of single-chain t-PA with that of two-chain t-PA and urokinase in a canine thrombosis model. The thrombolytic properties of single- and two-chain recombinant t-PA and urokinase with equivalent activity in vitro after intravenous infusion were examined in 24 anesthetized, open-chest dogs with intracoronary thrombi. Repeated coronary angiography showed that the time to reperfusion was 29.0 +/- 4.8, 32.5 +/- 6.3, and 39.2 +/- 6.8 min, respectively. One dog in the single-chain t-PA group and all dogs in the vehicle group showed no recanalization. Plasma t-PA antigen reached similar plateau levels within 15. min in both the single- and two-chain t-PA groups. The infusion of single- and two-chain t-PA was not associated with systemic fibrinolytic activation, except for a decrease in alpha 2-plasmin inhibitor in single-chain t-PA. However, the infusion of urokinase was associated with significant depletion of fibrinogen. These findings suggest that single-chain t-PA has potent thrombolytic effect without systemic fibrinolytic activity similar to that of two-chain t-PA in a canine coronary artery thrombosis model.

Animals↗

PubMed1996

Modulation of pump function by mutations in the first transmembrane region of Na(+)-K(+)-ATPase alpha 1-subunit.

The Cys in the first transmembrane region of the Na(+)-K(+)-adenosinetriphosphatase (ATPase) alpha 1-subunit has been shown to be a critical determinant of cardiac glycoside binding. To study the role of this Cys on ion transport activity, we measured pump currents in HeLa cells expressing wild-type or mutant alpha 1-subunit cDNAs. The endogenous ouabainsensitive Na(+)-K(+)-ATPase was selectively inhibited by growing the cells in 0.1 microM ouabain. A Cys-to-Tyr substituted mutant exhibited decreased sensitivity to digitoxin but not digoxin compared with wild type. The decreased affinity for digitoxin was due to a faster dissociation rate. In contrast, the Cys-to-Ala substitution did not significantly alter the sensitivity to digitoxin or digoxin. Both wild-type and mutant cells displayed marked external K(+)-dependent pump currents; however, the affinity for K+ was reduced by the mutations. The decrease in K+ affinity was due to a slower association rate. The results show that the Cys that interacts with cardiac glycosides also participates in the sensitivity of the pump to external K+.

Amino Acid Sequence↗

PubMed1995

Block of P-type Ca2+ channels in freshly dissociated rat cerebellar Purkinje neurons by diltiazem and verapamil.

We investigated the effects of organic Ca2+ channel blockers, diltiazem and verapamil, on the high voltage-activated P-type Ca2+ channels in freshly isolated rat Purkinje neurons. Both diltiazem and verapamil blocked P-type Ca2+ channel current without any change in the current-voltage relation. The block was concentration-dependent. In the presence of these agents, the inactivation curve was shifted to hyperpolarizing potentials. The characteristics of block of P-type Ca2+ channels by diltiazem and verapamil are similar to that of L-type Ca2+ channels. These results indicate that both benzothiazepine and phenylalkylamine react with P-type Ca2+ channels and suggest that some structural features common to which operate in both L-type and P-type Ca2+ channels may be involved in drug binding to these channels.

Animals↗

PubMed1995

A novel enhancing effect of clofilium on transient outward-type cloned cardiac K+ channel currents.

1. The antiarrythmic drug, clofilium, has been shown to block several types of K+ channel currents. To investigate the effects of clofilium on the transient outward K+ current (Ito), a cloned Ito-type cardiac K+ channel (RHK1) was expressed in Xenopus oocytes and the drug effects were examined on whole cell currents. 2. Extracellular application of clofilium slightly inhibited the current at +60 mV from a holding potential of -80 mV. However, it unexpectedly enhanced the current from a holding potential of -60 mV in a dose-dependent manner (219 +/- 39% of control at 100 microM). 3. This enhancement is probably due to an increase in the ratio of channels in the resting state during steady depolarization, since clofilium shifted the inactivation curve in the depolarizing direction. 4. LY97119, a tertiary ammonium analogue of clofilium, did not exhibit this enhancing effect but only inhibited the current. 5. Clofilium may be useful for the study of channel inactivation because this type of phenomenon has not been reported for any other drug.

Animals↗