The functional activity of inhibitory G protein (G(i)) is not increased in failing heart ventricle.

Beta-adrenergic receptor (ßAR) inotropic effects are attenuated and muscarinic receptor-mediated inhibition thereof is enhanced in heart failure. We investigated if increased G(i) activity contributes to attenuated ßAR-inotropic effects and potentiates muscarinic accentuated antagonism in failing rat ventricle. Contractility was measured in ventricular strips and adenylyl cyclase (AC) activity in ventricular membranes from rats with post-infarction heart failure (HF) or Sham-operated controls (Sham). The maximal ßAR-mediated inotropic effect of isoproterenol was reduced by ~70% and basal, ßAR- & forskolin-stimulated AC activity was significantly lower in HF vs. Sham. Carbachol-evoked antagonism of the ßAR-mediated inotropic response was complete only in HF despite a ~40% reduction in the ability of carbachol to inhibit ßAR-stimulated AC. However, neither the relative efficacy (contractility decreased by ~46%) nor the potency of carbachol to inhibit the ßAR inotropic response differed between Sham and HF ventricle. Pertussis toxin (PTX) inactivation of G(i) did not increase the maximal ßAR inotropic effect or the attenuated basal, ßAR- & forskolin-stimulated AC activity in HF, but increased the potency of isoproterenol only in Sham (~0.5 log unit). In HF ventricle pretreated with PTX, simultaneous inhibition of phosphodiesterases 3,4 (PDE3,4) alone produced a larger inotropic response than isoproterenol in ventricle untreated with PTX (84% and 48% above basal respectively). In the absence of PTX, PDE3,4 inhibition evoked negligible inotropic effects in HF. These data are not consistent with the hypothesis that increased G(i) activity contributes to the reduced ßAR-mediated inotropic response and AC activity in failing ventricle. The data, however, support the hypothesis that G(i), through chronic receptor independent inhibition of AC, together with PDE3,4 activity, is necessary to maintain a low basal level of contractility.

Effects of treatment with a 5-HT4 receptor antagonist in heart failure.

BACKGROUND AND PURPOSE: Positive inotropic responses (PIR) to 5-hydroxytryptamine (5-HT) are induced in the left ventricle (LV) in rats with congestive heart failure (CHF); this is associated with upregulation of the G(s)-coupled 5-HT(4) receptor. We investigated whether chronic 5-HT(4) receptor blockade improved cardiac function in CHF rats. EXPERIMENTAL APPROACH: Rats were given either the 5-HT(4) antagonist SB207266 (0.5 mg kg(-1) 24h(-1); MI(int)) or placebo (MI(pl)) through mini-osmotic pumps for 6 weeks subsequent to induction of post-infarction CHF. In vivo cardiac function and ex vivo responses to isoprenaline or 5-HT were evaluated using echocardiography and isolated LV papillary muscles, respectively. mRNA levels were investigated using real-time quantitative RT-PCR. KEY RESULTS: LV diastolic function improved, with 4.6% lower LV diastolic diameter and 24.2% lower mitral flow deceleration in MI(int) compared to MI(pl). SB207266 reduced LV systolic diameter by 6.1%, heart weight by 10.2% and lung weight by 13.1%. The changes in posterior wall thickening and shortening velocity, cardiac output, LV systolic pressure and (dP/dt)(max), parameters of LV systolic function, did not reach statistical significance. The PIR to isoprenaline (10 microM) increased by 36% and the response to 5-HT (10 microM) decreased by 57% in MI(int) compared to MI(pl). mRNA levels for ANP, 5-HT(4(b)) and 5-HT(2A) receptors, MHCbeta, and the MHCbeta/MHCalpha -ratio were not significantly changed in MI(int) compared to MI(pl). CONCLUSIONS AND IMPLICATIONS: Treatment with SB207266 to some extent improved in vivo cardiac function and ex vivo myocardial function, suggesting a possible beneficial effect of treatment with a 5-HT(4) receptor antagonist in CHF.

Cyclic AMP formation and morphology of myocardial cells isolated from adult heart: effect of Ca2+ and Mg2+.

Adult rat heart cells were isolated by perfusion with a calcium-free phosphate buffer containing collagenase. Optimal conditions gave a high proportion of elongated cells. Isoprenaline increased cydic AMP content linearly, with ED50 (dose effective in 50% of the population) about 10(-7) M. Ca2+ made the cells spherical, and it nearly abolished cyclic AMP response as did lack of Mg2+.

Specific binding of [3H]prazosin to myocardial cells isolated from adult rats.

The characteristics of alpha-adrenoceptors in rat myocardium were investigated by specific binding of [3H]prazosin to cells isolated from adult rat heart by perfusion with collagenase and hyaluronidase. The cells were incubated in Krebs-Ringer bicarbonate buffer gassed with 95% O2 and 5% CO2 at 31 degrees with the appropriate concentrations of the different ligands. Non-specific binding was defined by the addition of 10(-5) mole/l. phentolamine. The binding of [3H]prazosin was saturable and reached equilibrium within 15 min. Scatchard analysis showed a straight line giving an apparent dissociation constant, Kd, equal to 155.9 +/- 8.0 pmole/l. and a maximal number of binding sites equal to 76.7 +/- 11.1 fmole/mg protein. Inhibition of specific [3H]prazosin binding by different adrenergic blockers showed the order of potency characteristic of alpha 1-adrenoceptors: prazosin much greater than phentolamine greater than yohimbine much greater than propranolol. Inhibition by adrenergic agonists showed the order of potency: adrenaline greater than noradrenaline = phenylephrine greater than isoprenaline. The same orders of potency were observed in the presence of propranolol. However, propranolol slightly decreased the affinity for noradrenaline and phenylephrine. Hofstee analyses of the inhibition curves showed two binding components for all ordinary alpha-adrenoceptor blockers and agonists including unlabelled prazosin. In contrast, [3H]prazosin showed only one binding component. Both binding components were of the alpha 1-adrenoceptor subtype according to the order of potency of blockers. The different ligands had different affinity ratios for the two binding components giving them different profiles. Trifluoperazine, a phenothiazine compound, also had high affinity for the [3H]prazosin binding sites. This drug, however, apparently detected one class of binding sites only, as interpreted from the Hofstee analysis. Hill analyses of the inhibition data consistently yielded Hill constants, nH, in the range 0.75-0.85 except for [3H]prazosin, where nH = 1.02 and for trifluoperazine, where nH = 1.07. Although the two binding components may serve different functions, it seems impossible at present to relate the negative and the positive inotropic components, respectively, of the alpha-adrenergic inotropic response observed in functional studies only to one or the other binding component.

Location of alpha 1-adrenoceptors relative to beta-adrenoceptors in rat myocardium.

Electrically driven rat papillary muscles (1 Hz) were examined for the location of their alpha 1-adrenoceptor and beta-adrenoceptor populations relative to each other. We determined the horizontal position of the dose-response curves for the positive inotropic effects exerted by noradrenaline in the absence and presence of the neuronal uptake blocker cocaine and in the absence and presence of the beta-adrenoceptor antagonist timolol and of the alpha 1-adrenoceptor antagonist prazosin. Cocaine slightly shifted the dose-response curves for alpha 1-adrenoceptor stimulation to a lower concentration of agonist. In contrast, the dose-response curve for beta-adrenoceptor stimulation was markedly shifted by cocaine to a lower concentration of agonist. Experiments with corticosterone (an extraneuronal uptake blocker) revealed no differential shift of either of the dose-response curves. Together, these data indicate that the alpha 1-adrenoceptor population is located more distantly from the adrenergic nerve terminals than the beta 1-adrenoceptor population in rat myocardium.

Similar localisation of alpha1- and beta-adrenoceptors in rabbit heart in relation to sympathetic nerve endings.

Electrically driven (1 Hz) rabbit papillary muscles were examined ex vivo for the localisation of the alpha1- and beta-adrenoceptor populations relative to the sympathetic nerve endings and to each other. We determined the influence of neuronal uptake blockade by cocaine upon the horizontal position of the dose-response curves for the inotropic and lusitropic effects exerted by noradrenaline in the presence of extra neuronal uptake blockade by hydrocortisone and in the presence and absence of adrenoceptor blockers. Cocaine similarly shifted the dose-response curves for both alpha1- and beta-adrenoceptors mediated effects to 10-30 times lower concentrations of noradrenaline. This potentiation by cocaine indicates that also the alpha1-adrenoceptor population is located close to or within the sympathetic synaptic clefts, as is known for the beta-adrenoceptor population.

Enhancement of the alpha-adrenergic inotropic component of noradrenaline by simultaneous stimulation of muscarinic acetylcholine receptors in rat myocardium.

The contribution of an alpha-adrenoceptor-mediated component to the final inotropic response to noradrenaline in the absence and presence of muscarinic acetylcholine receptor stimulation (which exerts a 'functional' antagonism of effects mediated through beta-adrenoceptors but not through alpha-adrenoceptors) was evaluated by recording contraction and relaxation in isolated, paced rat papillary muscles. In the absence of muscarinic acetylcholine receptor stimulation, the alpha 1-selective adrenoceptor blocker prazosin (0.12 microM) did not significantly influence the dose-dependent response to noradrenaline with respect to either contractility or to relaxation. In the presence of concomitant muscarinic acetylcholine receptor stimulation by 10 microM carbachol, prazosin reduced by 32% (alpha = 0.028) the maximal increase in contractility (expressed as (dT/dt)max) evoked by noradrenaline compared to the absence of prazosin. Prazosin also did not influence the effect of noradrenaline upon relaxation under these conditions. Carbachol itself did not significantly reduce the maximal contractile response to noradrenaline. Thus cholinergic stimulation increases both relatively and absolutely the alpha-adrenergic inotropic component of noradrenaline. These observations indicate a ternary regulatory system of myocardial contractility through the autonomic receptors.

Alpha 1-adrenoceptor subtypes involved in increased 86Rb+ influx rate and inositol 1,4,5-trisphosphate mass in adult rat cardiomyocytes.

The aim of the present study was to identify the receptor subtypes involved in the alpha 1-adrenoceptor-mediated increase in 86Rb+ influx rate and in inositol 1,4,5-trisphosphate (IP3) accumulation in isolated ventricular cardiomyocytes from adult rat heart, in order to identify a possible response pattern compatible with a causative relationship. Subtype-selective receptor antagonists used were: 5-methylurapidil (alpha 1A), WB 4101 [2([2,6-dimethoxyphenoxy-ethyl]aminomethyl)-1,4-benzodioxane] (alpha 1A), chloroethylclonidine (alpha 1B) and BMY 7378 [8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4,5]dec ane-7,9-dione] (alpha 1D). The basal 86Rb+ influx rate was 0.22 +/- 0.01 ml/g protein x min. At 15 min, 5 x 10(-5) mol/l noradrenaline in the presence of 3 x 10(-5) mol/l timolol increased the 86Rb+ influx rate by 33 +/- 1%. This response was not affected by either chloroethylclonidine or BMY 7378 at concentrations up to 10(-5) mol/l. 5-Methylurapidil dose dependently inhibited the response to 5 x 10(-5) mol/l noradrenaline with a -logIC50 value of 5.27 +/- 0.12 and 5.61 +/- 0.27 in the presence and absence of 10(-5) mol/l chloroethylclonidine, respectively. WB 4101 in the presence of 10(-5) mol/l chloroethylclonidine dose dependently inhibited the response to 5 x 10(-5) mol/l noradrenaline with a -logIC50 value of 6.10 +/- 0.14. Noradrenaline in the presence of 10(-5) mol/l chloroethylclonidine dose dependently increased the 86Rb+ uptake rate with a -logEC50 value of 6.19 +/- 0.35. The basal IP3 level was 2.15 +/- 0.19 pmol/mg protein. Incubation with 10(-5) mol/l noradrenaline for 2 min increased this by 65 +/- 7% of control levels. 10(-5) mol/l chloroethylclonidine and 10(-4) mol/l 5-methylurapidil reduced the response to 27 +/- 6% and 18 +/- 9% of control level, respectively. BMY 7378 dose dependently inhibited the IP3 response at relatively high concentrations, and it was completely eliminated at 10(-5) mol/l BMY 7378. The combination of chloroethylclonidine and 5-methylurapidil or 3 x 10(-6) mol/l prazosin alone completely abolished the hormone-induced effect. We conclude that whereas the alpha 1-adrenoceptor-stimulated increase in 86Rb+ influx rate is mediated via the alpha 1A-adrenoceptor subtype only, both alpha 1A- and alpha 1B-adrenoceptor subtypes are involved in the increase in IP3 mass. Furthermore, a contribution from the alpha 1D-adrenoceptor in the IP3 response cannot be excluded. Thus there does not appear to be a simple causative relationship between an increase in 86Rb+ influx rate and an increase in IP3.

Differential effects of cocaine on the positive inotropic effect of noradrenaline mediated by alpha1- and beta-adrenoceptors in failing human myocardium.

Electrically driven (1 Hz) ventricular trabeculae from explanted failing human myocardium were indirectly examined for the localization of the alpha1-adrenoceptor population and the beta-adrenoceptor population in relation to sympathetic nerve endings. We examined the influence of neuronal uptake blockade by cocaine upon the horizontal position of the concentration-response curves for the inotropic effects exerted by noradrenaline in the presence and absence of appropriate adrenoceptor antagonists. Cocaine shifted the concentration-response curve for alpha1-adrenoceptor stimulation, but not that for beta-adrenoceptor stimulation, to lower concentrations of noradrenaline in a parallel manner. The concentration-response curve for combined adrenoceptor stimulation was shifted by cocaine to lower concentrations of noradrenaline in a nonparallel manner. In explanted allograft heart, cocaine had no effect upon the position of the concentration-response curve to alpha1-adrenoceptor stimulation. The data indicate that in the explanted native hearts the alpha1-adrenoceptor population is located close to or within the synaptic cleft, while the beta-adrenoceptor population remaining in the failing myocardium is located more distantly to the neuronal release sites.

Anti-M2 muscarinic receptor antibodies inhibit beta-adrenoceptor-mediated inotropic response in rat myocardium.

The modulation of the inotropic effect by affinity-purified antibodies against a synthetic peptide corresponding to the second extracellular loop of the human muscarinic M2 receptors was studied in adult rat ventricular myocardium. These anti-muscarinic M2 receptor antibodies shifted the dose-response relationship of the beta-adrenoceptor agonist isoproterenol to higher concentrations whereas preimmune rabbit immunoglobulin G (IgG) or antibodies against the N-terminus of the beta 1-adrenoceptor had no effect. This effect of anti-muscarinic M2 receptor antibodies was fully blocked after preincubation with the antigenic peptide. No significant change of maximal inotropic response to isoproterenol was observed in the presence of anti-muscarinic M2 receptor antibodies. The anti-muscarinic M2 receptor antibodies did apparently not hamper the access of the muscarinic receptor agonist carbachol. The muscarinic receptor antagonist atropine attenuated the effect of the anti-muscarinic M2 receptor antibodies. The present study demonstrates for the first time in intact adult ventricular myocardium a specific stimulatory muscarinic activity of antibodies raised against a part of the muscarinic M2 receptor protein.

Inhibition of phosphodiesterase-3 by levosimendan is sufficient to account for its inotropic effect in failing human heart.

BACKGROUND AND PURPOSE: Levosimendan is known as a calcium sensitizer, although it is also known to inhibit PDE3. We aimed to isolate each component and estimate their contribution to the increased cardiac contractility induced by levosimendan. EXPERIMENTAL APPROACH: Contractile force was measured in electrically stimulated ventricular strips from explanted failing human hearts and left ventricular strips from normal male Wistar rats. PDE activity was measured in a two-step PDE activity assay on failing human ventricle. KEY RESULTS: Levosimendan exerted a positive inotropic effect (PIE) reaching maximum at 10(-5) M in ventricular strips from failing human hearts. In the presence of the selective PDE3 inhibitor cilostamide, the PIE of levosimendan was abolished. During treatment with a PDE4 inhibitor and a supra-threshold concentration of isoprenaline, levosimendan generated an amplified inotropic response. This effect was reversed by ß-adrenoceptor blockade and undetectable in strips pretreated with cilostamide. Levosimendan (10(-6) M) increased the potency of ß-adrenoceptor agonists by 0.5 log units in failing human myocardium, but not in the presence of cilostamide. Every inotropic response to levosimendan was associated with a lusitropic response. Levosimendan did not affect the concentration-response curve to calcium in rat ventricular strips, in contrast to the effects of a known calcium sensitizer, EMD57033 [5-(1-(3,4-dimethoxybenzoyl)-1,2,3,4-tetrahydroquinolin-6-yl)-6-methyl-3,6-dihydro-2H-1,3,4-thiadiazin-2-one]. PDE activity assays confirmed that levosimendan inhibited PDE3 as effectively as cilostamide. CONCLUSIONS AND IMPLICATIONS: Our results indicate that the PDE3-inhibitory property of levosimendan was enough to account for its inotropic effect, leaving a minor, if any, effect to a calcium-sensitizing component.

SERCA2 activity is involved in the CNP-mediated functional responses in failing rat myocardium.

BACKGROUND AND PURPOSES: Myocardial C-type natriuretic peptide (CNP) levels are increased in heart failure. CNP can induce negative inotropic (NIR) and positive lusitropic responses (LR) in normal hearts, but its effects in failing hearts are not known. We studied the mechanism of CNP-induced NIR and LR in failing hearts and determined whether sarcoplasmatic reticulum Ca(2+) ATPase2 (SERCA2) activity is essential for these responses. EXPERIMENTAL APPROACH: Contractility, cGMP levels, Ca(2+) transient amplitudes and protein phosphorylation were measured in left ventricular muscle strips or ventricular cardiomyocytes from failing hearts of Wistar rats 6 weeks after myocardial infarction. KEY RESULTS: CNP increased cGMP levels, evoked a NIR and LR in muscle strips, and caused phospholamban (PLB) Ser(16) and troponin I (TnI) Ser(23/24) phosphorylation in cardiomyocytes. Both the NIR and LR induced by CNP were reduced in the presence of a PKG blocker/cGMP analogue (Rp-8-Br-Pet-cGMPS) and the SERCA inhibitor thapsigargin. CNP increased the amplitude of the Ca(2+) transient and increased SERCA2 activity in cardiomyocytes. The CNP-elicited NIR and LR were not affected by the L-type Ca(2+) channel activator BAY-K8644, but were abolished in the presence of isoprenaline (induces maximal activation of cAMP pathway). This suggests that phosphorylation of PLB and TnI by CNP causes both a NIR and LR. The NIR to CNP in mouse heart was abolished 8 weeks after cardiomyocyte-specific inactivation of the SERCA2 gene. CONCLUSIONS AND IMPLICATIONS: We conclude that CNP-induced PLB and TnI phosphorylation by PKG in concert mediate both a predictable LR as well as the less expected NIR in failing hearts.

Cyclic AMP-dependent inotropic effects are differentially regulated by muscarinic G(i)-dependent constitutive inhibition of adenylyl cyclase in failing rat ventricle.

BACKGROUND AND PURPOSE: ß-Adrenoceptor (ß-AR)-mediated inotropic effects are attenuated and G(i) proteins are up-regulated in heart failure (HF). Muscarinic receptors constitutively inhibit cAMP formation in normal rat cardiomyocytes. We determined whether constitutive activity of muscarinic receptors to inhibit adenylyl cyclase (AC) increases in HF and if so, whether it modifies the reduced ß-AR- or emergent 5-HT4-mediated cAMP-dependent inotropic effects. EXPERIMENTAL APPROACH: Contractility and AC activity were measured and related to each other in rat ventricle with post-infarction HF and sham-operated (Sham) controls with or without blockade of muscarinic receptors by atropine and inactivation of G(i) protein by pertussis toxin (PTX). KEY RESULTS: Isoprenaline-mediated inotropic effects were attenuated and basal, isoprenaline- and forskolin-stimulated AC activity was reduced in HF compared with Sham. Atropine or PTX pretreatment increased forskolin-stimulated AC activity in HF hearts. ß-AR-stimulated AC and maximal inotropic response were unaffected by atropine in Sham and HF. In HF, the potency of serotonin (5-HT) to evoke an inotropic response was increased in the presence of atropine with no change in the maximal inotropic response. Interestingly, PTX pretreatment reduced the potency of 5-HT to evoke inotropic responses while increasing the maximal inotropic response. CONCLUSIONS AND IMPLICATIONS: Although muscarinic constitutive inhibition of AC is increased in HF, it does not contribute to the reduced ß-AR-mediated inotropic effects in rat ventricle in HF. The data support the hypothesis that there are differences in the functional compartmentation of 5-HT4 and ß-AR AC signalling in myocardium during HF.

Zinc- and copper-induced interleukin-6 release in primary cell cultures from rat heart.

The metals, zinc (Zn2+) and copper (Cu2+) from inhaled particulate matter may reach the systemic circulation and the cardiac tissue. In the present study, the potential of Zn2+ and Cu2+ to induce interleukin (IL)-6 responses in cardiomyocytes (CMs) and cardiac fibroblasts (CFs), in mono- and cocultures, was examined. Both metals induced IL-6 release in a concentration (20-200 microM)-dependent manner. Zn2+ appeared more potent than Cu2+ in both mono- and cocultures of CMs and CFs. In the cocultures, the basal- and metal-induced IL-6 responses were synergistically increased compared to the monocultures. Exposure to Zn2+ increased phosphorylation of the MAP-kinases, ERK1/2 and p38, in monocultures of CMs and CFs. Cu2+ induced an increased phosphorylation of p38 in both cell types and of ERK1/2 in CFs, but at higher concentrations than Zn2+. Treatment with a p38 inhibitor (SB202190) reduced the IL-6 responses to Zn2+ and Cu2+ in both cell types. Pretreatment with PD98059 to inhibit ERK1/2 was without significant effect; however, insignificant reductions was observed in the in the CFs. In conclusion, Zn2+ and Cu2+ increased IL-6 release and MAP-kinase activation in primary cardiac cells, processes known to be involved in cardiac inflammation and hypertrophy.

Activation of muscarinic receptors elicits inotropic responses in ventricular muscle from rats with heart failure through myosin light chain phosphorylation.

BACKGROUND AND PURPOSE: Muscarinic stimulation increases myofilament Ca(2+) sensitivity with no apparent inotropic response in normal rat myocardium. Increased myofilament Ca(2+) sensitivity is a molecular mechanism promoting increased contractility in failing cardiac tissue. Thus, muscarinic receptor activation could elicit inotropic responses in ventricular myocardium from rats with heart failure, through increasing phosphorylation of myosin light chain (MLC). EXPERIMENTAL APPROACH: Contractile force was measured in left ventricular papillary muscles from male Wistar rats, 6 weeks after left coronary artery ligation or sham surgery. Muscles were also frozen, and MLC-2 phosphorylation level was quantified. KEY RESULTS: Carbachol (10 micromol.L(-1)) evoked a positive inotropic response only in muscles from rats with heart failure approximating 36% of that elicited by 1 micromol.L(-1) isoproterenol (20 +/- 1.5% and 56 +/- 6.1% above basal respectively). Carbachol-evoked inotropic responses did not correlate with infarction size but did correlate with increased left ventricular end diastolic pressure, heart weight/body weight ratio and lung weight, primary indicators of the severity of heart failure. Only muscarinic receptor antagonists selective for M(2) receptors antagonized carbachol-mediated inotropic effects with the expected potency. Carbachol-evoked inotropic responses and increase in phosphorylated MLC-2 were attenuated by MLC kinase (ML-9) and Rho-kinase inhibition (Y-27632), and inotropic responses were abolished by Pertussis toxin pretreatment. CONCLUSION AND IMPLICATIONS: In failing ventricular muscle, muscarinic receptor activation, most likely via M(2) receptors, provides inotropic support by increasing MLC phosphorylation and consequently, myofilament Ca(2+) sensitivity. Enhancement of myofilament Ca(2+) sensitivity, representing a less energy-demanding mechanism of inotropic support may be particularly advantageous in failing hearts.

5-HT4-elicited positive inotropic response is mediated by cAMP and regulated by PDE3 in failing rat and human cardiac ventricles.

BACKGROUND AND PURPOSE: The left ventricle in failing hearts becomes sensitive to 5-HT parallelled by appearance of functional G(s)-coupled 5-HT(4) receptors. Here, we have explored the regulatory functions of phosphodiesterases in the 5-HT(4) receptor-mediated functional effects in ventricular muscle from failing rat and human heart. EXPERIMENTAL APPROACH: Extensive myocardial infarctions were induced by coronary artery ligation in Wistar rats. Contractility was measured in left ventricular papillary muscles of rat, 6 weeks after surgery and in left ventricular trabeculae from explanted human hearts. cAMP was quantified by RIA. KEY RESULTS: In papillary muscles from postinfarction rat hearts, 5-HT(4) stimulation exerted positive inotropic and lusitropic effects and increased cAMP. The inotropic effect was increased by non-selective PDE inhibition (IBMX, 10 microM) and selective inhibition of PDE3 (cilostamide, 1 microM), but not of PDE2 (EHNA, 10 microM) or PDE4 (rolipram, 10 microM). Combined PDE3 and PDE4 inhibition enhanced inotropic responses beyond the effect of PDE3 inhibition alone, increased the sensitivity to 5-HT, and also revealed an inotropic response in control (sham-operated) rat ventricle. Lusitropic effects were increased only during combined PDE inhibition. In failing human ventricle, the 5-HT(4) receptor-mediated positive inotropic response was regulated by PDEs in a manner similar to that in postinfarction rat hearts. CONCLUSIONS AND IMPLICATIONS: 5-HT(4) receptor-mediated positive inotropic responses in failing rat ventricle were cAMP-dependent. PDE3 was the main PDE regulating this response and involvement of PDE4 was disclosed by concomitant inhibition of PDE3 in both postinfarction rat and failing human hearts. 5-HT, PDE3 and PDE4 may have pathophysiological functions in heart failure.

Defective excitation-contraction coupling in hearts of rats with congestive heart failure.

AIM: We examined the cellular basis for depressed cardiac contractility in rats with congestive heart failure (CHF) secondary to myocardial infarction. METHODS: Six weeks after ligation of the left coronary artery, CHF was confirmed by haemodynamic measures and echocardiographic demonstration of reduced myocardial contractility in vivo. Papillary muscles from CHF animals developed less force than those from sham operated (SHAM) animals. Cell shortening was measured in isolated ventricular myocytes voltage-clamped with high resistance electrodes. Ca2+ transients were measured in fluo-4 loaded myocytes. RESULTS: Contractions triggered by depolarizing test steps from a post conditioning potential of -70 mV were significantly smaller and had significantly reduced velocity of shortening in CHF compared with SHAM myocytes. However, contractions initiated from -40 mV, were similar in amplitude and velocity of shortening in CHF and SHAM cells. L-type Ca2+ current was not significantly different between CHF and SHAM cells, whether activated from -70 or -40 mV. Therefore, in SHAM cells, excitation-contraction coupling exhibited higher gain when contractions were initiated from negative (-70 mV), as compared with depolarized potentials (-40 mV). However, in CHF myocytes, excitation-contraction coupling gain was selectively depressed with steps from -70 mV. This depression of gain in CHF was not accompanied by a significant reduction in sarcoplasmic reticulum Ca2+ content. Isoproterenol increased Ca2+ transients less in CHF than SHAM myocytes. CONCLUSION: In this post-infarction model of CHF, the contractile deficit was voltage dependent and the gain of excitation-contraction coupling was selectively depressed for contractions initiated negative to -40 mV.

[Gingival hyperplasia induced by calcium channel blockers. Rare or frequent in Norway?]. / Kalsiumkanalblokkerindusert gingival hyperplasi. Sjelden, eller tusener av tilfeller i Norge?

Sales statistics indicate that the number of Norwegians treated with calcium channel blockers increased from about 50,000 in 1986 to about 83,000 in 1991 (last year: nifedipine 39%, verapamil 27%, amlodipine 21%, diltiazem 10% and felodipine 3%). In spite of widespread use, only one report on gingival hyperplasia induced by calcium channel blockers has been received by the Norwegian Adverse drug reaction committee. The incidence of this adverse reaction is uncertain, but the few controlled studies that have been performed indicate that it may be as high as 15% in patients on long-term treatment, at least with nifedipine. This corresponds to nearly 5,000 cases among the about 32,000 users of nifedipine. Norwegian physicians and dentists are asked to report cases of gingival hyperplasia induced by calcium channel blockers. Although the voluntary report system is fraught with uncertainty, it is hoped that, in a relatively small and surveyable drug market as the Norwegian, the reporting may provide some relevant information, e.g. to allow comparison of the potential of the various calcium channel blockers to induce this adverse effect. A Norwegian controlled study on gingival conditions among long-term users of calcium channel blockers is in its initial stage. It may be of interest to compare the results of this study with the indications obtained from the spontaneous reporting on the incidence of this adverse effect, which is relatively easy to diagnose.