Biomedical subjects

C Mundiña

Publications and source records attributed to C Mundiña.

7 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↗

PubMed1992

Positive lusitropic effect and diminished myofibrillar sensitivity to calcium produced by cAMP on toad (Bufo arenarum Hensel) ventricle.

In intact ventricular strips from toad heart, we studied the relaxant or positive lusitropic effect of different interventions known to increase intracellular cAMP levels. Isoproterenol increased developed tension (DT), maximal rate of contraction (+T), and maximal velocity of relaxation (-T). From 10(-8) to 10(-4)M isoproterenol, -T increased proportionally more than +T being the ratio +T/-T significantly decreased. A single dose of isoproterenol (3 x 10(-8)M) increased cAMP levels from 0.174 +/- 0.022 to 0.329 +/- 0.039 pmoles/mg ww (P < 0.05), increased contractility by 69 +/- 13% and decreased +T/-T by 18.5 +/- 4.55%. Administration of 10(-3)M of dibutyryl cyclic AMP (dcAMP) significantly increased DT and +T and decreased the ratio +T/-T. Similar effects were obtained with milrinone, a specific cAMP phosphodiesterase inhibitor. Papaverine, a non selective phosphodiesterase inhibitor, failed to increase +T but significantly increased -T. In chemically skinned ventricular trabeculae, calcium sensitivity of the myofibrils was significantly increased by 10(-5)M of the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine (IBMX). 10(-3)M dcAMP failed to affect calcium sensitivity of chemically skinned ventricular trabeculae when given alone, but produced a decrease in calcium sensitivity of the myofibrils in the presence of 10(-5)M of either IBMX or papaverine. The results would indicate that the relaxant effect of isoproterenol is mediated in toad ventricle by an increase in intracellular cAMP levels. They furthermore suggest that a decrease in myofilament sensitivity to calcium may be a mechanism by which cAMP produces its relaxant effect.

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

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↗

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↗