Search PubMed⌕ Search

Biomedical subjects

J Sadoshima

Publications and source records attributed to J Sadoshima.

At least 37 records · Page 2Linked to original sources
PubMed1996

The heterotrimeric G q protein-coupled angiotensin II receptor activates p21 ras via the tyrosine kinase-Shc-Grb2-Sos pathway in cardiac myocytes.

p21 ras plays as important role in cell proliferation, transformation and differentiation. Recently, the requirement of p21 ras has been suggested for cellular responses induced by stimulation of heterotrimeric G protein-coupled receptors. However, it remains to be determined how agonists for G protein-coupled receptors activate p21 ras in metazoans. We show here that stimulation of the G q protein-coupled angiotensin II (Ang II) receptor causes activation of p21 ras in cardiac myocytes. The p21 ras activation by Ang II is mediated by an increase in the guanine nucleotide exchange activity, but not by an inhibition of the GTPase-activating protein. Ang II causes rapid tyrosine phosphorylation of Shc and its association with Grb2 and mSos-1, a guanine nucleotide exchange factor of p21 ras. This leads to translocation of mSos-1 to the membrane fraction. Shc associates with the SH3 domain of Fyn whose tyrosine kinase activity is activated by Ang II with a similar time course as that of tyrosine phosphorylation of Shc. Ang II-induced increase in the guanine nucleotide exchange activity was inhibited by a peptide ligand specific to the SH3 domain of the Src family tyrosine kinases. These results suggest that an agonist for a pertussis toxin-insensitive G protein-coupled receptor may initiate the cross-talk with non-receptor-type tyrosine kinases, thereby activating p21 ras using a similar mechanism as receptor tyrosine kinase-induced p21 ras activation.

Adaptor Proteins, Signal Transducing↗
PubMed1996

Conditional differentiation of heart- and smooth muscle-derived cells transformed by a temperature-sensitive mutant of SV40 T antigen.

To create muscle cell lines that conditionally differentiate in vitro we introduced a temperature-sensitive SV40 T antigen by retroviral infection into rat aortic smooth muscle cells (SMCs) and neonatal heart-derived cells. After G418 selection cell lines isolated were characterized at permissive (33 degrees C) and non-permissive (39 degrees C) temperatures. [3H]Thymidine uptake showed tht progression through the cell cycle is greatly reduced at 39 degrees C. Cytoskeletal proteins, such as actins and vimentin did not change significantly after temperature shift, while the number of desmin-positive SMCs significantly increased when cells were switched to 39 degrees C. Heart-derived muscle cells showed sarcomeric myosin heavy chain reactivity only when grown at 39 degrees C. After thrombin stimulation intracellular calcium in both cell types increased severalfold in 39 degrees C-cells but not in 33 degrees C-cells. Whole cell patch-clamp recordings of SMCs and heart-derived cells revealed a strong increase in nicardipine-sensitive Ca2+ current when cells were switched to 39 degrees C. Nicardipine-insensitive Ca2+ current also increased in both cell types at the non-permissive temperature. Na+ current in SMCs was large at 33 degrees C and small or not detectable at 39 degrees C and absent in heart-derived cells. Using a cDNA probe specific for the alpha 1 subunit of the dihydropyridine-sensitive Ca2+ channel we demonstrate a temperature-sensitive expression of the dihydropyridine receptor mRNA in smooth muscle-derived cells but not in heart-derived H10 cells. Our results suggest that upon downregulation of SV40 T antigen these cells become quiescent and exhibit a more differentiated phenotype. These cell lines may provide a useful tool to investigate ion channel- and receptor signal transduction, as well as cell cycle control in smooth and possibly cardiac muscle cell differentiation.

Animals↗
PubMed1995

Angiotensin II and other hypertrophic stimuli mediated by G protein-coupled receptors activate tyrosine kinase, mitogen-activated protein kinase, and 90-kD S6 kinase in cardiac myocytes. The critical role of Ca(2+)-dependent signaling.

Many hypertrophic stimuli such as angiotensin II (Ang II) activate phospholipases through G protein-coupled receptors in cardiac myocytes. However, it is not known whether these stimuli also activate the tyrosine phosphorylation-dependent signaling pathway, which plays an essential role in growth factor-induced mitogenic responses in other cell types. Serine/threonine kinases such as mitogen-activated protein (MAP) kinases and 90-kD S6 kinase (RSK) are activated in response to many growth stimuli and are important downstream signaling pathways of tyrosine kinases. Therefore, we examined whether Ang II activates these protein kinases in primary cultures of cardiac myocytes and fibroblasts from neonatal rats. Ang II rapidly induced tyrosine phosphorylation of multiple proteins, including 42-, 44-, 75- to 80-, and 120- to 130-kD proteins, in both cardiac myocytes and fibroblasts. This was accompanied by an increase in tyrosine kinase activity. The 42- and 44-kD proteins were immunologically related to an extracellular signal-regulated kinase family (MAP kinases). Ang II rapidly increased kinase activity of MAP kinases and their downstream kinase, RSK. The Ang II-induced tyrosine phosphorylation and activation of MAP kinases and RSK were AT1 receptor-mediated. Activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate or an increase in intracellular Ca2+ by the Ca2+ ionophore A23187 was sufficient to cause tyrosine phosphorylation of multiple proteins and activation of MAP kinase and RSK. Although downregulation of PKC did not suppress Ang II-induced activation of MAP kinase and RSK, chelating intracellular Ca2+ by BAPTA-AM completely abolished Ang II-induced activation of these kinases. Activation of MAP kinases and RSK was also observed in myocytes stimulated with other agonists for Gq protein-coupled receptors, such as phenylephrine, norepinephrine, and endothelin 1, but not with agonists to Gs protein-coupled receptors, such as isoproterenol. These results suggest that Ang II and other hypertrophic stimuli, known to act through Gq protein-coupled receptors, rapidly cause tyrosine phosphorylation of several intracellular substrates through activation of tyrosine kinase and activate MAP kinases and RSK in cardiac myocytes as well as in cardiac fibroblasts. Furthermore, intracellular Ca2+, rather than PKC, seems to be critical for Ang II-induced activation of these protein kinases in cardiac myocytes.

Angiotensin II↗
PubMed1995

Angiotensin II-induced growth responses in isolated adult rat hearts. Evidence for load-independent induction of cardiac protein synthesis by angiotensin II.

Cardiac myocyte hypertrophy often occurs in response to both hemodynamic and neurohumoral factors. To study whether activation of the renin-angiotensin system by itself may induce a cardiac growth response, the acute effects of angiotensin II on cardiac protein synthesis were studied in isolated rat hearts. New protein synthesis in isolated buffer-perfused adult rat hearts was measured by incorporation of [3H]phenylalanine into cardiac proteins during a 3-hour perfusion protocol. Angiotensin II (1 x 10(-8) mol/L), administered alone or in combination with the alpha 1-blocker prazosin (1 x 10(-7) mol/L), stimulated protein synthesis in both ventricles. The rate of [3H]phenylalanine incorporation into cardiac proteins was 3.9-fold (P < .005) and 2.6-fold (P < .01) higher in angiotensin II-perfused (n = 6) than in vehicle-perfused (n = 6) left and right ventricles, respectively. The induction of new protein synthesis by angiotensin II was blocked by the angiotensin II type 1 (AT1) receptor antagonist losartan (1 x 10(-7) mol/L, n = 5). To study the pathways of angiotensin signal transduction, protein kinase C (PKC)-epsilon as well as cardiac c-fos and c-jun mRNA levels were analyzed. Angiotensin II (1 x 10(-8) mol/L, n = 20) resulted in a transient translocation of PKC-epsilon from the cytosol to the cellular membrane. However, compared with phorbol ester stimulation (phorbol 12-myristate 13-acetate [PMA], 1 x 10(-7) mol/L; n = 20), angiotensin II effects on PKC translocation were significantly less pronounced and required a more prolonged stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1995

Rapamycin selectively inhibits angiotensin II-induced increase in protein synthesis in cardiac myocytes in vitro. Potential role of 70-kD S6 kinase in angiotensin II-induced cardiac hypertrophy.

It has been suggested that phosphorylation of a 40S ribosomal protein, S6, regulates protein synthesis. Two distinct families of S6 kinase have been identified, the rsk-encoded 85- to 92-kD S6 kinase (RSK) and the 70- or 85-kD S6 kinase (p70S6K). We have previously shown that hypertrophic stimuli, such as angiotensin II (Ang II), rapidly activate RSK in cardiac myocytes. However, RSK and p70S6K are regulated by distinct mechanisms, and p70S6K, but not RSK, is the physiological S6 kinase in vivo in other cell types. Using cultured neonatal rat ventricular myocytes, we examined whether Ang II activates p70S6K and investigated the effect of rapamycin, a potent yet indirect inhibitor of p70S6K, on the Ang II-induced hypertrophic response. Immunoblot analyses indicate that cardiac myocytes express the 70- and 85-kD forms of p70s6K. Ang II caused a rapid and sustained activation of p70S6K through the type I Ang II receptor. Rapamycin inhibited Ang II-induced activation of p70S6K in a dose-dependent manner, with an IC50 of 0.14 ng/mL (0.15 nmol/L). Rapamycin did not inhibit Ang II-induced activation of tyrosine kinase, mitogen-activated protein kinase, RSK, and protein kinase C. The effect of rapamycin is unlikely to be mediated by its effect on p34cdc2 and p33cdk2 because Ang II did not activate these cell cycle-dependent kinases in cardiac myocytes. In contrast, a dose-dependent inhibition of p70S6K by rapamycin is very closely correlated with its inhibition of the Ang II-induced increase in protein synthesis. Interestingly, rapamycin did not affect the Ang II-induced activation of specific gene expression, including the immediate-early gene c-fos and fetal type genes, such as atrial natriuretic factor and skeletal alpha-actin. Moreover, rapamycin did not suppress Ang II-induced phenotypic changes at the protein level, such as increased atrial natriuretic factor secretion, expression of beta-myosin heavy chain, and organization of actin into sarcomeric units. These results indicate that p70S6K is activated by Ang II and that a rapamycin-sensitive signaling mechanism, most likely p70S6K, plays an essential role in the Ang II-induced increase in overall protein synthesis but not in Ang II-induced specific phenotypic changes in cardiac myocytes.

Analysis of Variance↗
PubMed1994

Cyclins and cyclin-dependent kinases are differentially regulated during terminal differentiation of C2C12 muscle cells.

Differentiation of skeletal myoblasts into contractile myotubes is associated with permanent withdrawal from the cell cycle. Little is known about the expression of cell cycle regulating genes during terminal differentiation of muscle cells. We investigated the expression pattern, biological activity, and cellular localization of cyclins and cyclin-dependent kinases during terminal differentiation of the mouse skeletal myogenic cell line C2C12. After induction of differentiation by serum deprivation, cdc2 mRNA levels transiently increased, followed by a down-regulation to undetectable levels within 42 h. In contrast, cdk2 mRNA stayed constant during this period. During differentiation cyclin A, B, and C were down-regulated within 24 h to undetectable levels. Interestingly, cyclin D1/CYL1 mRNA was up-regulated by twofold at 9-12 h after serum deprivation followed by a down-regulation to undetectable levels within 42 h, while cyclin D3/CYL3 mRNA levels remained constant. Restimulation of the differentiated myotube culture with serum reinduced cdc2 as well as cyclin D1/CYL1 mRNA close to the levels observed in dividing myoblasts. At the protein level p34cdc2 was detected in nuclei of proliferating myoblasts and nascent myotubes, but not in mature myotubes. Restimulation with serum-induced p34cdc2 protein in a small minority of unfused myoblasts, but never in myotubes. Histone H1 kinase activity of p34cdc2 decreased during differentiation while p33cdk2 activity did not change. These findings suggest that terminal differentiation of skeletal muscle cells is associated with a differential regulation of cyclins and their associated kinases. Inability to accumulate p34cdc2 protein in response to serum stimulation, despite the induction of its mRNA, in differentiated myotubes may play an important role in maintaining the postmitotic state of skeletal muscle in the presence of high concentrations of growth factors.

Animals↗
PubMed1994

Right-to-left shunt across atrial septal defect related to tricuspid regurgitation: assessment by transesophageal Doppler echocardiography.

The purpose of this study was to assess the factors involved in the development of the right-to-left (R-L) shunt in patients with atrial septal defect (ASD), especially the role of tricuspid regurgitation (TR). Thirty-one consecutive patients with ASD underwent transesophageal Doppler echocardiography to determine the size of ASD, the shunt flow, and the TR flow, and they were compared with hemodynamics examined by cardiac catheterization. Sixteen patients with the R-L shunt were older (53 +/- 11 vs 34 +/- 9 years; p < 0.001) and had higher pulmonary arterial pressure (36 +/- 17 vs 25 +/- 5 mmHg; p < 0.05) and a greater Qp/Qs (3.6 +/- 1.2 vs 2.4 +/- 0.9 L/min; p < 0.01) as compared with 15 patients with the pure left-to-right shunt. In six of 21 patients with TR, the regurgitant flow oriented toward ASD and blew into the left atrium through the defect. Besides the deviation of TR flow, the prevalences of the maximum diameter of ASD > 2.5 cm and the maximal TR flow area > 4 cm2 were significantly higher in the six patients as compared with patients with TR not related to the R-L shunt (p < 0.05 and p < 0.05), despite the pulmonary arterial pressure being similar in the two groups. Reversal of pressure gradient between the left and right atrium was not observed during the cardiac cycle in all patients. In conclusion, TR is a determinant of the R-L shunt in patients with ASD even in the absence of the reversal of pressure gradient between the left and right atrium.

Adolescent↗
PubMed1993

Autocrine release of angiotensin II mediates stretch-induced hypertrophy of cardiac myocytes in vitro.

Hypertrophy is a fundamental adaptive process employed by postmitotic cardiac and skeletal muscle in response to mechanical load. How muscle cells convert mechanical stimuli into growth signals has been a long-standing question. Using an in vitro model of load (stretch)-induced cardiac hypertrophy, we demonstrate that mechanical stretch causes release of angiotensin II (Ang II) from cardiac myocytes and that Ang II acts as an initial mediator of the stretch-induced hypertrophic response. The results not only provide direct evidence for the autocrine mechanism in load-induced growth of cardiac muscle cells, but also define the pathophysiological role of the local (cardiac) renin-angiotensin system.

Actins↗
PubMed1993

Mechanical stretch rapidly activates multiple signal transduction pathways in cardiac myocytes: potential involvement of an autocrine/paracrine mechanism.

It is well known that external load plays a critical role in determining cardiac muscle mass and its phenotype, but little is known as to how mechanical load is transduced into intracellular signals regulating gene expression. To address this question we analyzed the 'mechano-transcription' coupling process using an in vitro model of load-induced cardiac hypertrophy, in which a stretch of rat cardiac myocytes, grown on a deformable substrate, causes a rapid induction of immediate-early genes followed by growth (hypertrophic) response. We report here that cell stretch rapidly activates a plethora of second messenger pathways, including tyrosine kinases, p21ras, mitogen-activated protein (MAP) kinases, S6 kinases (pp90RSK), protein kinase C, phospholipase C, phospholipase D, and probably the phospholipase A2 and P450 pathways. In contrast, the cAMP pathway is not activated significantly by stretch. The signals generated by these second messengers appear to converge into activation of the p67SRF-p62TCF complex via the serum response element, causing induction of c-fos. The stretch response may involve an autocrine or paracrine mechanism, because stretch-conditioned medium, when transferred to non-stretched myocytes, mimicked the effect of stretch. These results indicate that mechanical load causes rapid activation of multiple second messenger systems, which may in turn initiate a cascade of hypertrophic response of cardiac myocytes.

Animals↗
PubMed1993

Molecular characterization of angiotensin II--induced hypertrophy of cardiac myocytes and hyperplasia of cardiac fibroblasts. Critical role of the AT1 receptor subtype.

Increasing evidence suggests that angiotensin II (Ang II) may act as a growth factor for the heart. However, direct effects of Ang II on mammalian cardiac cells (myocytes and nonmyocytes), independent of secondary hemodynamic and neurohumoral effects, have not been well characterized. Therefore, we analyzed the molecular phenotype of cultured cardiac cells from neonatal rats in response to Ang II. In addition, we examined the effects of selective Ang II receptor subtype antagonists in mediating the biological effects of Ang II. In myocyte culture, Ang II caused an increase in protein synthesis without changing the rate of DNA synthesis. In contrast, Ang II induced increases in protein synthesis, DNA synthesis, and cell number in nonmyocyte cultures (mostly cardiac fibroblasts). The Ang II-induced hypertrophic response of myocytes and mitogenic response of fibroblasts were mediated primarily by the AT1 receptor. Ang II caused a rapid induction of many immediate-early genes (c-fos, c-jun, jun B, Egr-1, and c-myc) in myocyte and nonmyocyte cultures. Ang II induced "late" markers for cardiac hypertrophy, skeletal alpha-actin and atrial natriuretic factor expression, within 6 hours in myocytes. Ang II also caused upregulation of the angiotensinogen gene and transforming growth factor-beta 1 gene within 6 hours. Induction of immediate-early genes, late genes, and growth factor genes by Ang II was fully blocked by an AT1 receptor antagonist but not by an AT2 receptor antagonist. These results indicate that: (1) Ang II causes hypertrophy of cardiac myocytes and mitogenesis of cardiac fibroblasts, (2) the phenotypic changes of cardiac cells in response to Ang II in vitro closely mimic those of growth factor response in vitro and of load-induced hypertrophy in vivo, (3) all biological effects of Ang II examined here are mediated primarily by the AT1 receptor subtype, and (4) Ang II may initiate a positive-feedback regulation of cardiac hypertrophic response by inducing the angiotensinogen gene and transforming growth factor-beta 1 gene.

Angiotensin II↗
PubMed1993

Signal transduction pathways of angiotensin II--induced c-fos gene expression in cardiac myocytes in vitro. Roles of phospholipid-derived second messengers.

Angiotensin II (Ang II) causes a rapid induction of immediate-early genes and hypertrophy in the cardiac myocyte. However, the signaling mechanism of Ang II-induced immediate-early gene expression in cardiac myocytes has not been characterized. Therefore, we examined signal transduction of Ang II in neonatal rat cardiac myocytes, using c-fos gene expression as a model system. Transient transfection of c-fos reporter gene constructs indicated that the serum response element is not only required but also sufficient for Ang II-induced activation of the c-fos promoter. Ang II is known to cause an increase in [Ca2+]i. We found that Ang II also causes a small increase in cAMP in cardiac myocytes. However, the Ca2+/cAMP response element of the c-fos gene was not sufficient to confer Ang II responsiveness to the c-fos promoter, and inhibitors of protein kinase A had no effects on Ang II-induced c-fos expression. On the other hand, chelating intracellular Ca2+ with BAPTA-AM inhibited Ang II-induced c-fos expression in a dose-dependent manner, suggesting that Ca2+ is required for Ang II-induced signaling. Measurements of phospholipid-derived second messengers revealed that Ang II increased production of inositol trisphosphate, diacylglycerol, phosphatidic acid, and arachidonic acids, resulting in a sustained increase in protein kinase C activity. This and other evidence suggest that Ang II activates phospholipase C, phospholipase D, and possibly phospholipase A2. All of these second-messenger systems are activated through the AT1 receptor. Pharmacological inhibition of phospholipase C or downregulation of protein kinase C significantly suppressed Ang II-induced c-fos expression. In conclusion, Ang II activates multiple phospholipid-derived second-messenger systems via the AT1 receptor in cardiac myocytes. Among these second-messenger systems, phospholipase C and protein kinase C seem essential for Ang II-induced c-fos gene expression, whereas Ca2+ may play a permissive role. Finally, the "Ang II response element" of the c-fos gene maps to the protein kinase C-dependent portion of the serum response element.

Adenylyl Cyclases↗
PubMed1993

Mechanotransduction in stretch-induced hypertrophy of cardiac myocytes.

Mechanical loading of cardiac muscles causes rapid activation of a number of immediate-early (IE) genes and hypertrophy. However, little is known as to how muscle cells sense mechanical load and regulate gene expression. We examined roles of several putative mechanotransducers in stretch-induced hypertrophy of cardiac myocytes grown on a deformable silicone sheet. Using the patch-clamp technique, we found a single class of stretch-activated cation channels which was completely and reversibly blocked by gadolinium. The inhibition of this channel by gadolinium did not affect either stretch-induced expression of the IE genes or hypertrophy. Neither disruption of microtubules with colchicine nor that of actin microfilaments by cytochalasin D prevented the stretch-induced IE gene expression. Arresting contractile activity by tetrodotoxin did not affect the stretch-induced IE gene expression or hypertrophy. These results suggest that stretch-activated cation channels, microtubules, microfilaments, and contractile activity are not the mechanotransducers. Preliminary results suggest that cell stretch may cause a release of a growth factor(s), which in turn initiates a cascade of hypertrophic response of cardiac myocytes.

Amino Acid Sequence↗
PubMed1992

Roles of mechano-sensitive ion channels, cytoskeleton, and contractile activity in stretch-induced immediate-early gene expression and hypertrophy of cardiac myocytes.

Mechanical loading of cardiac and skeletal muscles in vivo and in vitro causes rapid activation of a number of immediate-early (IE) genes and hypertrophy of muscle cells. However, little is known as to how muscle cells sense mechanical load and transduce it into intracellular signals of gene regulation. We examined roles of putative cellular mechanotransducers, mechanosensitive ion channels, the cytoskeleton, and contractile activity in stretch-induced hypertrophy of cardiac myocytes grown on a deformable silicone sheet. Using the patch-clamp technique, we found a single class of stretch-activated cation channel that was completely blocked by gadolinium (Gd3+). Inhibition of this channel by Gd3+ did not affect either the stretch-induced expression of IE genes or the increase in protein synthesis. Neither disruption of microtubules with colchicine nor that of actin microfilaments by cytochalasin D prevented the stretch-induced IE gene expression and increase in protein synthesis. Arresting contractile activity of myocytes by high K+, tetrodotoxin, or Ba2+ did not affect the stretch-induced IE gene expression. Tetrodotoxin-arrested myocytes could increase protein synthesis in response to stretch. These results suggest that Gd(3+)-sensitive ion channels, microtubules, microfilaments, and contractile activity may not be necessary for transduction of mechanical stretch into the IE gene expression and hypertrophy. The stimulus of membrane stretch may be transmitted to the cell nucleus through some mechanisms other than electrical or direct mechanical transduction in cardiac myocytes.

Amino Acid Sequence↗
PubMed1992

Molecular characterization of the stretch-induced adaptation of cultured cardiac cells. An in vitro model of load-induced cardiac hypertrophy.

Although it is a well-known fact that hemodynamic load is a major determinant of cardiac muscle mass and its phenotype, little is known as to how mechanical load is converted into intracellular signals of gene regulation. To address this question, we characterized the stretch-induced adaptation of cultured neonatal cardiocytes grown on a stretchable substrate in a serum-free medium. Static stretch (20%) of the cells was applied without cell injury. Stretch caused hypertrophy in myocytes and hyperplasia in non-myocytes. Stretch caused an induction of immediate-early genes such as c-fos, c-jun, c-myc, JE, and Egr-1, but not Hsp70. Immunostaining showed that the stretch-induced Fos protein localized in the nucleus of both myocytes and non-myocytes. Nuclear extracts from stretched myocytes contained DNA binding activity to the AP-1 and Egr-1 consensus sequences. In myocytes, the induction of immediate-early genes was followed by expression of "fetal" genes such as skeletal alpha-actin, atrial natriuretic factor, and beta-myosin heavy chain. DNA transfection experiments showed that the "stretch-response element" of the c-fos gene promoter is present within 356 base pairs of the 5'-flanking region, whereas that of the atrial natriuretic factor and the beta-myosin heavy chain genes is probably located outside of 3412 and 628 base pairs of the 5'-flanking region, respectively. These results demonstrate that the phenotype of stretched cardiocytes in this in vitro model closely mimics that of hemodynamic load-induced hypertrophy in vivo. This model seems to be a suitable system with which to dissect the molecular mechanisms of load-induced hypertrophy of cardiac muscle.

Adaptation, Physiological↗
PubMed1992

Evaluation of the severity of mitral regurgitation by transesophageal Doppler flow echocardiography.

The severity of mitral regurgitation (MR) was assessed by transesophageal Doppler flow echocardiography (TEE) using new criteria in 87 patients. The severity of MR assessed by TEE (TEE-MR) was compared with that obtained by left ventriculography (LVG-MR). Although the severity of TEE-MR has been evaluated by MR jet area, it is often difficult because the MR jet extends beyond a single frame image in severe MR. We found that (1) when the MR area was larger than 3 cm2, the severity of MR was more than second-degree by LVG; (2) there was systolic turning flow (STF) of the MR jet within the left atrial cavity in 27 of 30 patients with third- and fourth-degree LVG-MR; and (3) there was late systolic backward flow (SBF) in the pulmonary veins in 9 of 10 patients with fourth-degree LVG-MR. A new grading of the severity of MR by TEE was proposed, which combined the findings of STF, SBF, and the MR area. These new criteria of the severity of TEE-MR excellently correlated with that by LVG (y = 0.94x + 0.08; r = 0.95, p less than 0.01). The criteria for MR by TEE were also useful for assessment of MR in patients with prosthetic mitral valve dysfunction (y = 0.96x + 0.04; r = 0.97, p less than 0.01). We conclude from this study that the severity of MR can be accurately assessed with TEE by measuring the MR area and the specific flow patterns in the left atrium and pulmonary veins.

Adolescent↗
PubMed1991

Kinetic properties of the caffeine-induced transient outward current in bull-frog sympathetic neurones.

1. The kinetic properties of the caffeine-induced transient outward current (ICaff) of the bull-frog sympathetic neurone were investigated using the extremely rapid concentration-jump technique. By setting the holding potential at the equilibrium potential for Cl- (-50 mV), the involvement of the Ca(2+)-activated Cl- current was suppressed. Using a Na(+)-free (Tris) external solution, the involvement of the Na(+)-dependent sustained outward current was eliminated. The 'M' conductance was also occluded by pre-treatment with muscarine. Under these experimental conditions, ICaff consisted of a TEA-sensitive Ca(2+)-activated K+ current. 2. When the latent period from the application of caffeine until the onset of ICaff (termed the ICaff latency) was measured, 10 mM-caffeine gave a latency of 10.5 +/- 0.7 ms (n = 14, mean +/- S.E.M.) at 22 degrees C. The latency was independent of caffeine concentration between 3 and 30 mM. 3. The ICaff latency was temperature-dependent; it was shortened when the temperature was elevated. 4. Both the time to peak and half-decay time of ICaff were decreased with increasing caffeine concentration. In each cell, these parameters decreased by increasing the amplitude of ICaff. 5. At 22 degrees C, the time to peak and the half-decay time of ICaff elicited by 10 mM-caffeine showed a linear relationship, and this relationship was preserved on either elevating or lowering the temperature. On lowering the temperature (12 degrees C), the time to peak shortened whereas the half-decay time was prolonged. On elevating the temperature (32 degrees C), the time to peak was prolonged whereas the half-decay time was shortened. 6. When EGTA in the intracellular solution was replaced by equimolar BAPTA, the time to peak was prolonged while the half-decay time was shortened. 7. It is concluded that caffeine can activate ICaff, with a time course in the order of milliseconds, and that the kinetics of activation and inactivation of ICaff reflect the time-dependent change in the total amount of intracellular free Ca2+.

Acetylcholine↗