Biomedical subjects

A Mattiazzi

Publications and source records attributed to A Mattiazzi.

13 recordsLinked to original sources

PubMed1992

Phosphorylation of phospholamban in the intact heart. A study on the physiological role of the Ca(2+)-calmodulin-dependent protein kinase system.

The aim of the present study was to further elucidate the physiological role of the calcium-calmodulin (Ca(2+)-Cm)-dependent protein kinase system on phospholamban phosphorylation in the intact functioning heart. The effect of increasing extracellular calcium concentration [Ca]o on phospholamban phosphorylation (PHPL) was studied under different experimental conditions: (a) regular twitches and ryanodine induced-tetani both in the presence and in the absence of 3 x 10(-8) M isoproterenol and (b) Post-stimulation potentiation (PSP), i.e. the potentiation of contractility that follows a period of rapid repetitive stimulation. In the regular twitch, the increase in [Ca]o enhanced contractility both, in the absence and in the presence of beta-stimulation without changing basal or isoproterenol stimulated cAMP levels respectively. This increase in contractility was accompanied by a significant enhancement of PHPL-from 90.6 +/- 16.4 to 216 +/- 35.2 pmols 32Pi/mg protein at 0.25 and 3.85 mM [Ca]o respectively-only when isoproterenol was present. The calmodulin antagonist W-7 significantly decreased the isoproterenol-induced phosphorylation of phospholamban at [Ca]o 1.35 mM. Similar results were obtained under tetanic conditions. When myocardial contractility was enhanced by PSP up to ten-times with respect to the regular twitch, no detectable effect in PHPL was observed. Indirect evidence obtained from skinned rat cardiac trabeculae suggested that the failure of the cAMP-independent mechanisms to phosphorylate phospholamban is not related to a deficient increase in intracellular calcium. The results support the notion that the increase in intracellular calcium induces an increase in PHPL only at high intracellular cAMP levels.

Animals↗

PubMed1991

Decrease in tetanic tension elicited by beta-adrenergic stimulation.

The effect of beta-adrenergic stimulation on tetanic tension (TT), maximal rate of rise of tension (+TT) and phospholamban (PHL) phosphorylation were studied in the perfused rat heart. 3 x 10(-8) M isoproterenol perfused at different [Ca2+]o 0.25, 1.35 and 3.85 mM, significantly decreased TT while increased +TT and PHL phosphorylation at the three [Ca2+]o studied. Regression lines of the relationship between +TT and TT from individual data obtained at each [Ca2+]o in the presence and in the absence of isoproterenol, show that for the same level of +TT, TT is lower in the presence of isoproterenol, i.e. at high levels of PHL phosphorylation. The slopes of the lines were 0.137 s and 0.427 s (P less than 0.05) in the presence and absence of isoproterenol respectively. The decrease in TT produced by the beta-agonist can be attributed to its relaxant action prevailing over its inotropic effect and may represent the mechanical expression of the enhanced phosphorylation of phospholamban.

Animals↗

PubMed1990

Calcium sensitivity of isometric tension in intact papillary muscles and chemically skinned trabeculae in different models of hypertensive hypertrophy.

STUDY OBJECTIVE - The aim was to examine the contractile state, the inotropic response to [Ca2+]e and the Ca2+ sensitivity of the contractile proteins in different models of hypertensive hypertrophy in an early stage of evolution (3-4 weeks). DESIGN - Renal hypertension was induced by placing a silver clip around the left renal artery. The contralateral kidney was either removed (1K-1C) or left untouched (2K-1C). Hypertension through sodium overload was produced by administration of deoxycorticosterone and 1% NaCl drinking water. (DOCA rats). Active and passive length-tension curves were performed to evaluate basal contractility at Lmax and passive stiffness of cardiac muscle. The inotropic responsiveness to [Ca2+]e and the Ca2+ sensitivity of the contractile proteins were also evaluated. EXPERIMENTAL MATERIAL - Papillary muscles and skinned trabeculae from the left ventricle of male Wistar hypertensive and age matched normotensive rats were used. MEASUREMENTS AND RESULTS - Cardiac hypertrophy was similar in all hypertensive groups. In 2K-1C and 1K-1C rats, basal contractility was not significantly different from controls. In DOCA rats, developed tension and time to peak tension (TTP) were significantly greater than controls. The inotropic response to [Ca2+]e was depressed in 2K-1C and increased in DOCA rats. In DOCA rats, increasing [Ca2+]e produced an increase in TTP greater than in controls. No differences were detected in muscle passive stiffness or in Ca2+ sensitivity of the contractility proteins among the different groups. CONCLUSIONS - In the earlier stages of hypertensive hypertrophy, differences in basal contractile state and/or inotropic responsiveness appear to be more related to the initiating cause of hypertensive hypertrophy than to the degree of hypertrophy itself. These differences cannot be attributed to changes in Ca2+ sensitivity of the contractile system.

Animals↗

PubMed1990

Sarcomere dynamics during isotonic velocity transients in single frog muscle fibers.

If the load on a tetanized fiber is abruptly changed to a new steady value, the ensuing fiber length change shows the well-known "isotonic velocity transient," in which the velocity oscillates before settling at some steady value. We studied sarcomere dynamics during these transients using two methods: optical diffraction and a segment-length method. Our principal aim was to determine whether these transients might be a reflection of the fact that sarcomere shortening is often found to be stepwise. We found that pauses in sarcomere shortening occurred during the low-velocity phases of the transient and that steps of sarcomere shortening occurred during the high-velocity phases. Thus the isotonic transient appears to arise from the steps. In addition to the isotonic transient, we studied the well-known isometric transient, in which fiber length is abruptly changed, and ensuing tension response is measured. Again, we found that the transient may be a reflection of the stepwise shortening pattern.

Animals↗

PubMed1990

cAMP and calcium-dependent mechanisms of phospholamban phosphorylation in intact hearts.

The present work was undertaken with two main goals: 1) to further elucidate the physiological role of the adenosine 3',5'-cyclic monophosphate (cAMP) and Ca2(+)-calmodulin (Ca2(+)-Cm)-dependent mechanisms of phospholamban phosphorylation (32PiPHL), and 2) to study the possible interaction between these two systems in the intact heart. Interventions that increased twitch or tetanic tension without modifying cAMP levels [high extracellular Ca2+ concentration [( Ca2+]o) or BAY K 8644 in catecholamine-depleted hearts] failed to alter 32PiPHL. Moderate and high beta-adrenergic stimulation (3 x 10(-9) and 3 x 10(-8) M isoproterenol, respectively) increased cAMP from 0.345 +/- 0.032 to 0.636 +/- 0.069 and 0.772 +/- 0.060 pmol/mg wet wt, and 32PiPHL from 26.8 +/- 4.1 to 58.6 +/- 13.1 and 174.7 +/- 13.8 pmol 32Pi/mg sarcoplasmic reticular [SR] protein, respectively. Both doses of isoproterenol produced an enhanced myocardial relaxation. Reversal of the positive inotropic effect of isoproterenol by interventions that decrease intracellular Ca2+ supply failed to reduce the enhancement in 32PiPHL and myocardial relaxation elicited by 3 x 10(-9) M isoproterenol but diminished the increase in 32PiPHL induced by 3 x 10(-8) M isoproterenol to 116.3 +/- 10.9 without significant changes in cAMP. Changes in myocardial relaxation closely paralleled the changes in 32PiPHL. These results suggest that 1) 32PiPHL may be enhanced by the cAMP-dependent mechanism independently of the Ca2(+)-Cm system, and 2) 32PiPHL and myocardial relaxation may be modified by intracellular Ca2+ changes only at high-intracellular cAMP levels.

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

PubMed1988

The effects of Bay K 8644 on myocardial relaxation and cAMP levels in perfused rat heart: role of sympathetic neurotransmitter release.

Bay K 8644 typifies a number of drugs known to act directly on voltage-dependent calcium channels to increase calcium current. Such effects probably underly the drug's positive inotropic action and smooth muscle stimulation. Although the effects of this compound on myocardial contractility have been extensively described, its action upon myocardial relaxation is not well established. Either no changes or a prolongation in ventricular relaxation have been mentioned. On the other hand, during the course of other experiments performed in our laboratory with the perfused rat heart (unpublished results), we observed that Bay K 8644 elicits a moderate but consistent relaxant effect. The present work was undertaken in an attempt to clarify the effect of Bay K 8644 upon myocardial relaxation. Evidence will be presented showing that in the perfused rat heart, the positive inotropic action of Bay K 8644 occurs together with a prolongation of the contraction time (TTP) without changes in time to half relaxation (t 1/2). However, an enhancement of ventricular relaxation was detected by the proportional greater increase in maximal velocity of relaxation (-T) with respect to maximal velocity of contraction (+T) and the shortening of the time constant of relaxation (tau). These actions occur associated with a significant increase in cAMP levels and phospholamban phosphorylation. Either the relaxant effect as well as the increments in cAMP and phospholamban phosphorylation were abolished when the hearts were depleted of norepinephrine by previous treatment with reserpine. Depletion of norepinephrine stores also decreases the positive inotropic effect of the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

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

PubMed1988

[Correlation between myocardial relaxation and phosphorylation of phospholamban].

The relationship between myocardial contractility and relaxation and phospholamban phosphorylation was studied in the isolated rat heart beating at a constant rate and perfused at constant coronary flow with a Ringer solution with 32Pi. At the end of the experiments, membrane vesicles, composed primarily of sarcoplasmic reticulum (SR), were isolated by differential centrifugation. Electrophoresis was performed on acrylamide-SDS gels. Perfusion with isoproterenol (ISO) significantly increased developed tension (T) by 40 +/- 8% and maximal rate of rise of tension (+T) by 76 +/- 12%. The ratio between +T and maximal velocity of relaxation (+T/-T) was significantly decreased from 1.65 +/- 0.04 to 1.23 +/- 0.04. Time to half relaxation (t 1/2) and the rate constant of relaxation (Tau) were significantly decreased by 27 +/- 2 y 6 +/- 1 msec respectively. When the increase in contractility produced by ISO was restored to control levels by addition of nifedipine (ISO-NIFE) or perfusion with low calcium (ISO-Ca+2), +T/-T decreased from 1.63 +/- 0.07 to 1.47 +/- 0.07 and 1.66 +/- 0.06 to 1.41 +/- 0.06 respectively, t 1/2 and Tau significantly decreased by 16 +/- 2 and 3 +/- 1 msec with ISO-NIFE and 19 +/- 2 and 5 +/- 1 msec with ISO-Ca+2 respectively. These decreases were significantly lower than those produced by ISO. Perfusion with high calcium significantly increased T and +T, without significant alterations in relaxation parameters. Phospholamban phosphorylation, in pmoles/mg of SR protein, increased from control values, 25 +/- 6 to 110 +/- 11 (ISO-NI-FE), 117 +/- 17 (ISO-Ca+2) and 197 +/- 21 (ISO) and did not change with high calcium. Results showed a striking correlation between relaxation parameters, +T/-T, t 1/2 and Tau, and phospholamban phosphorylation (r = -0.98, -0.99 and 0.96, respectively). This correlation was much lower between T and +T and phospholamban phosphorylation.

Animals↗

PubMed1988

Pauses, steps, and the mechanism of contraction.

Despite widespread controversy still surrounding the phenomenon, stepwise shortening has now been confirmed by five independent methods in this laboratory, and by several other methods in different laboratories. In this paper we offer preliminary evidence obtained with the most recent method--measurement of 'isotonic muscle length transients'. We find that the muscle length inflections observed after quick release to an isotonic load correspond to pauses and steps at the sarcomere level. Thus, pauses and steps are reflected not only in sarcomere length and segment length signals, but in the muscle length signal as well. We review several of the more illuminating features of stepwise shortening, as well as new ultrastructural observations which, taken together, point to an hypothesis for the generation of steps. The steps may be generated by shortening of one or another of the sarcomere's filaments: connecting filaments in the unactivated myofibril and thick filaments in the activated myofibril. Supporting evidence is considered.

Animals↗

PubMed1987

[Effect of alpha 1 adrenergic stimulation on myocardial relaxation].

The aim of the present study was to elucidate which was the effect of alpha 1 adrenergic stimulation on myocardial relaxation. Experiments were performed in cat papillary muscles contracting isometrically at 12 beats/min. The effect of phenylephrine (P) in the presence of propranolol (10(-6)M) on myocardial relaxation was compared with that produced by a similar increase in myocardial contractility (+T) elicited by increasing extracellular calcium (Ca2+). An increase of 40% in maximal velocity of contraction (+T) produced by P and Ca2+ elicited in both cases a proportional increase in maximal velocity of relaxation (-T). Therefore the +T/-T ratio remained unchanged. At this contractility level relaxation time (Rt) and time to half relaxation (t1/2) were slight by significantly prolonged by P and not changed by Ca2+. When contractility was increased by approximately 200%, both, P and Ca2+ increased by a less extent -T. Consequently +T/-T augmented from 1.21 +/- 0.04 to 1.73 +/- 0.09 (48.3 +/- 9.5%) with P, and from 1.37 +/- 0.04 to 1.77 +/- 0.15 (31 +/- 12%) with Ca2+. Rt was also significantly increased by both interventions: 21.5 +/- 8.8% (Ca2+) and 24.2 +/- 2.68% (P), whereas t1/2 was significantly increased by P from 215 +/- 11 msec to 282 +/- 12 msec (33 +/- 5.8%) but did not change with Ca2+. Prazosin (10(-6)M) antagonized the effects on contractility and relaxation produced by P. The present results thus indicate that the positive inotropic effect of alpha 1 adrenergic stimulation may be characterized by a prolongation of the early relaxation phase, that was not mimicked by a similar increase in myocardial contractility elicited by increasing extracellular calcium.

Animals↗

PubMed1987

[Inhibitory effect of propranolol on myocardial relaxation not mediated by beta blockade].

The effect of d- and d,l-propranolol (10(-5)M) on myocardial relaxation was studied in the isolated cat heart beating at constant rate and perfused at constant coronary flow. Infusion of d,l-propranolol 10(-5)M produced a significant decrease in maximal velocity of contraction (+T) of 48 +/- 1.5%, P less than 0.05, and a proportionally greater decrease in maximal velocity of relaxation (-T) of 58 +/- 2%, with a significant increase in the ratio between both maximal velocities (+T/-T) of 28.4 +/- 6.2% (from 1.35 +/- 0.03 to 1.74 0.09). The time constant of tension decline computed from the time of -T (Tau) was significantly prolonged by 64 +/- 17.5% (from 38 +/- 1.4 to 61 +/- 6 msec) (P less than 0.05). Similar results were obtained with d-propranolol (10(-5)M). A decrease in +T of 52.2 +/- 4.1% elicited by perfusion with low calcium (0.05 mM) also produced a slight increase in +T/-T and Tau by 11 +/- 4.5% and 27 +/- 6% respectively, P less than 0.05). These increases were, however, lower than those produced by both d,l- and d-propranolol (P less than 0.05). The effect of low calcium on +T, +T/-T and Tau were fully reversible, whereas the complete reversal by calcium of the negative inotropic effect of d- and d,l-propranolol did not reverse the significant decrease in -T and increase in +T/-T, and Tau elicited by the drug. Similar results were obtained in catecholamine depleted hearts. d-propranolol (10(-5)M) did not affect the calcium sensitivity of the chemically skinned cat right ventricular trabeculae. The calcium uptake of cat cardiac sarcoplasmic reticulum was significantly inhibited by d-propranolol from a concentration of 3 X 10(-4) M. The results suggest that propranolol 10(-5)M has an antirelaxant effect, not mediated by its negative inotropic action and independent of its beta blocking action. This antirelaxant effect might be mediated by the SR calcium uptake inhibition produced by the drug and might be a possible mechanism by which high concentrations of these agents negatively affect myocardial contractility.

Animals↗

PubMed1985

Renal hypertension impairs inotropic isoproterenol effect without beta-receptor changes.

Experiments were performed in male Wistar rats with renovascular hypertension (167 +/- 4.2 mmHg) produced by clipping the renal artery for a 3-wk period (2-kidney, 1-clip Goldblatt). The results were compared with those obtained in age-matched normotensive controls. Hypertension of 3-wk duration elicited a significant increase in ventricular weight (1.01 +/- 0.02 g) with respect to the controls (0.82 +/- 0.01 g) but had no significant effect on body weight. The inotropic responsiveness to beta-adrenergic stimulation was diminished in papillary muscles from renal hypertensive rats: the maximum increase in the maximal rate of rise of tension produced by isoproterenol was 27.39 +/- 5.4 and 11.77 +/- 2.91 g X mm-2 X s-1 (P less than 0.05) in control and hypertensive animals, respectively. Similar results were obtained when the estimated maximal velocity of shortening of the contractile element (Vmax) was used to assess myocardial contractility. The inotropic response to CaCl2 was also significantly depressed in the 2-kidney, 1-clip rats. However, the relaxant and the chronotropic responses to isoproterenol were not significantly modified in the Goldblatt rats. Assays of beta-adrenergic receptors to l-[3H]dihydroalprenolol binding, showed no significant changes in the number (expressed per mg of membrane protein) or in the affinity of the beta-receptors. These results suggest that at an early stage of the renal hypertensive model the impaired inotropic response to isoproterenol is not mediated by an alteration of the beta-receptors and should be searched at a postreceptor adenyl cyclase level.

Animals↗

PubMedDate not supplied

Dissociation between contraction and relaxation: the possible role of phospholamban phosphorylation.

The relationship between myocardial relaxation and phosphorylation of phospholamban, an intrinsic protein of sarcoplasmic reticulum (SR), was studied in perfused rat hearts beating at constant rate and perfused at constant coronary flow. The positive inotropic effect (increase in developed tension, T, and maximal rate of rise of tension, +T) of 3 X 10(-9) and 3 X 10(-8) M isoproterenol (ISO) occurred together, with a proportionately greater increase in maximal velocity of relaxation, -T. Thus, the +T/-T ratio decreased 0.23 +/- 0.04 and 0.41 +/- 0.05 respectively. Time to half-relaxation (t1/2) and the time constant of relaxation (Tau) were also significantly decreased by ISO. Phospholamban phosphorylation (in pmol 32Pi/mg SR protein) increased from 23 +/- 3.3 (control) to 42 +/- 2.3 (3 X 10(-9) M ISO) and to 186 +/- 19.3 (3 X 10(-8) M ISO). When the negative inotropic action of nifedipine was just offset by either Ca2+ (N-Ca2+) or ISO (N-I), relaxation was faster when ISO was present. Perfusion with N-I significantly decreased +T/-T 0.18 +/- 0.05, t1/2 14 +/- 3 ms and Tau 1.4 +/- 0.2 ms. Phospholamban phosphorylation significantly increased from 23 +/- 3.3 to 40 +/- 4.9 pmol 32 Pi/mg SR protein. N-Ca2+ did not elicit any significant change in these parameters nor in phospholamban phosphorylation. Thus, phospholamban phosphorylation appears closely related to myocardial relaxation and may be one of the important mechanisms by which contractility and relaxation are dissociated in vivo.

Adenosine Triphosphatases↗

PubMedDate not supplied

Characteristics of ryanodine-induced tetani in the perfused rat heart. Tetanic tension is not the highest force that cardiac muscle can generate.

The aim of the present study was to elucidate the conditions required to obtain tetanic contractions in rat intact heart and to investigate whether tetanic tension was actually the maximal tension that isolated rat heart is able to generate. Experiments were performed on isolated rat hearts (Langendorff technique) perfused at constant coronary flow (8-9 ml/min). Rapid repetitive stimulation (400 to 3000 pulses/min) failed to elicit a fused tetanus. The first twitch that occurred at the end of the rapid stimulation period was a potentiated beat (PSP) of significantly greater magnitude than that of the regular twitch. This potentiation declined in successive beats. When rapid electrical stimulation (600 to 3000 pulses/min) was applied to hearts treated with 5 x 10(-6) M ryanodine, the result was a fused and steady tetanic tension. Ryanodine suppressed PSP. Tetanic tension could be graded by stepwise increase of [Ca2+]o from 0.25 to 5 mM. Maximal tetanic tension occurred at a [Ca2+]o between 3.85 and 5 mM. At any of the [Ca2+]o, tetanic tension was significantly greater than the tension of the twitch obtained at approximately the natural frequency of rat heart in the intact animal (250 beats/min) but it did not differ significantly from the twitch obtained at 100 beats/min. Moreover, the tension of PSP at 0.25 and 1.35 mM [Ca2+]o was significantly greater than the maximal tetanic tension that could be obtained. Similar results to that obtained with ryanodine, were obtained in additional experiments in which caffeine was used to evoke tetanic contraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗