[Biliary ileus. Diagnosis and therapy]

Based on retrospective evaluation of therapeutic results of all patients operated at the Second Surgical Clinic of the Second Medical Faculty Charles University on account of biliary ileus during the last 10 years the authors submit their ideas on treatment of this relatively rare disease. Decisive for the patient is early, though frequently difficult assessment of the diagnosis and the speediest possible removal of the obstruction. Enterlithotomy with thorough revision of the gut above the obstruction and removal of the contents is a sufficiently effective procedure. Subsequent elective cholecystectomy is indicated only in patients with further symptoms of biliary disease and confirmed cholecystolithiasis.

Antiemetic efficacy of granisetron plus dexamethasone in bone marrow transplant patients receiving chemotherapy and total body irradiation

Few trials exist regarding the antiemetic efficacy of granisetron in bone marrow transplant (BMT) recipients conditioned with high-dose chemotherapy and total body irradiation (TBI). In this single-center, open-label, prospective, trial, the antiemetic efficacy and safety of granisetron plus dexamethasone were evaluated in 26 patients conditioned with cyclophosphamide-containing regimens (the majority receiving 60 mg/kg per day on 2 consecutive days), and TBI (12 Gy divided over 4 days). Daily intravenous doses of granisetron 1 mg plus dexamethasone 10 mg were given 30 min prior to chemotherapy or radiation, and continued for 24 h after the last conditioning treatment for a median of 6 days (range 3-9). Emetic control was defined by the number of emetic episodes occurring within a 24 h period, or the requirement for rescue medication for nausea or vomiting. A total of 25 patients completed 186 evaluable treatment days. Response (emetic control by treatment days) was complete in 50% of patients, major in 48%, minor in 2%, and there were no failures. Adverse effects were minor, with diarrhea (15%), headache (14%), and constipation (11%) reported most often. Based on these results, the antiemetic regimen of granisetron plus dexamethasone appears effective and well tolerated during BMT conditioning with high-dose cyclophosphamide and TBI.

Inotropic effects of diadenosine tetraphosphate (AP4A) in human and animal cardiac preparations

Diadenosine tetraphosphate (AP4A) is an endogenous compound and exerts diverse physiological effects in animal systems. However, the effects of AP4A on inotropy in ventricular cardiac preparations have not yet been studied. The effects of AP4A on force of contraction (FOC) were studied in isolated electrically driven guinea pig and human cardiac preparations. Furthermore, the effects of AP4A on L-type calcium current and [Ca]i were studied in isolated guinea pig ventricular myocytes. In guinea pig left atria, AP4A (0.1-100 microM) reduced FOC maximally by 36.5 +/- 4.3%. In guinea pig papillary muscles, AP4A (100 microM) alone was ineffective, but reduced isoproterenol-stimulated FOC maximally by 29.3 +/- 3.4%. The negative inotropic effects of AP4A in atria and papillary muscles were abolished by the A1-adenosine receptor antagonist 1, 3-dipropyl-cyclopentylxanthine. In guinea pig ventricular myocytes, AP4A (100 microM) attenuated isoproterenol-stimulated L-type calcium current and [Ca]i. In human atrial and ventricular preparations, AP4A (100 microM) alone increased FOC to 158.3 +/- 12.4% and 167.5 +/- 25.1%, respectively. These positive inotropic effects were abolished by the P2-purinoceptor antagonist suramin. On the other hand, AP4A (100 microM) reduced FOC by 27.2 +/- 7.4% in isoproterenol-stimulated human ventricular trabeculae. The latter effect was abolished by 1,3-dipropyl-cyclopentylxanthine. In summary, after beta adrenergic stimulation AP4A exerts negative inotropic effects in animal and human ventricular preparations via stimulation of A1-adenosine receptors. In contrast, AP4A alone can exert positive inotropic effects via P2-purinoceptors in human ventricular myocardium. Thus, P2-purinoceptor stimulation might be a new positive inotropic principle in the human myocardium.

Dissociation of the effects of forskolin and dibutyryl cAMP on force of contraction and phospholamban phosphorylation in human heart failure

Forskolin and dibutyryl cyclic adenosine monophosphate (cAMP) stimulate force of contraction independent of beta-adrenoceptor stimulation. We studied their effects on force of contraction and phosphorylation of regulatory proteins in isolated electrically driven trabeculae carneae from failing human ventricles. The phosphorylation state of the regulatory protein phospholamban was studied because its phosphorylation usually faithfully follows contractility. For comparison, the phosphorylation state of the inhibitory subunit of troponin was studied. The phosphorylation state was inferred from in vitro phosphorylation of homogenates with cAMP-dependent protein kinase in the presence of radioactive gamma[32P]ATP Proteins were separated by electrophoresis, and radioactivity in the proteins of interest was quantified. The maximal positive inotropic effects occurred at 30 microM forskolin and were attenuated in comparison with the maximal effects to dibutyryl cAMP (1 mM). Both forskolin and dibutyryl cAMP enhanced phospholamban phosphorylation. However, phospholamban phosphorylation in intact trabeculae treated with 30 microM forskolin and 1 mM dibutyryl cAMP was comparable. It is suggested that phospholamban phosphorylation can be dissociated from inotropy at least in isolated trabeculae from failing human hearts.

IDDM patients neither show humoral reactivities against endogenous retroviral envelope protein nor do they differ in retroviral mRNA expression from healthy relatives or normal individuals

Recently, human endogenous retrovirus type K (HERV-K [IDDMK(1,2)22]) was isolated from an IDDM patient's beta-cell supernatant and shown to be implicated in expression as a superantigen. Furthermore, HERV-K RNA was found in plasma samples from newly diagnosed patients but not in those from healthy control subjects. We had earlier identified the presence of a HERV-K long terminal repeat element of the HLA DQ gene (DQ-LTR) to be positively associated with IDDM, which led us to investigate whether DQ-LTR is related to transcription of the putative retroviral superantigen. Additionally, we sought immunological evidence to determine whether those retroviral antigens could evoke an antibody response. Patients with IDDM (n = 14), Hashimoto's thyroiditits (n = 5), and Graves' disease (n = 12), as well as healthy control subjects (n = 12), were investigated, as were four nuclear families of Graves' disease patients and two of IDDM patients. RNA was isolated from plasma and peripheral blood lymphocytes and subjected to reverse transcription-polymerase chain reaction for transcripts of the env region of the HERV-K (IDDMK(1,2)22) sequence. We identified env transcripts in both plasma and peripheral blood lymphocytes in all individuals studied: patients with recent-onset or long-standing IDDM, their relatives, and healthy control subjects, as well as patients with thyroid autoimmune disorders. Furthermore, we screened the sera of patients (n = 62) and control subjects (n = 35) for evidence of humoral immunity against HERV-K by Western blot specific for the ENV protein. Similar frequencies of antibody-positives were observed both in patients with IDDM (29%) and in healthy control subjects (26%). We conclude that neither the ubiquitous HERV-K transcripts nor the comparable percentage of ENV protein antibodies are associated with IDDM. An earlier, presymptomatic antibody response against HERV-K (IDDMK(1,22)22) ENV cannot be ruled out. However, the superantigen hypothesis of an endogenous retrovirus in beta-cell autoimmunity awaits confirmation.

[Surgical treatment of benign tumors of the thyroid gland]

Based on 22-year experience with surgery of 2107 benign thyroid tumours and data in the literature the authors evaluate some controversial problems from this sphere of thyrology pertaining to the definition and classification of benign tumours, their diagnosis, treatment and subsequent follow-up. Modern diagnostic procedures indicate that the actual number of true benign tumours is smaller than reported in some statistics and the assumption of monoclonal development of tumours is one of the most fundamental characteristics. The authors consider total lobectomy as minimal surgery, in case of uncertainty as regards possible malignancy further procedures depend on final histological examination. If the final finding alters the diagnosis from an originally benign tumour to a malignant one, the authors recommend a two-stage procedure to implement total thyroidectomy. In the authors' opinion total lobectomy is sufficient also in some variants of follicular adenoma--Hürtle's adenoma or atypical adenoma. Then however subsequent dispensarization is essential. After a partial operation (lobectomy) it is important to ensure substitution with thyroid hormones to suppress the function of TSH.

[Malignant lymphomas of the thyroid gland]

The authors evaluate their experience with malignant lymphomas of the thyroid gland, recorded in 22 patients from a total of 4501 operated on account of thyroid diseases in the course of 22 years. Although thyroid lymphomas are rare, their number is increasing. In localized findings curative procedures can be used, possibly supplemented by operations of the lymph nodes. The method of choice is still radiotherapy and surgery, in particular in lesions restricted to the thyroid gland. The role of chemotherapy is still controversial.

Inotropic effects of diadenosine tetraphosphate in isolated canine cardiac preparations

We studied the effects of diadenosine tetraphosphate (AP4A) on the force of contraction in canine preparations. The force of contraction was measured in isolated electrically driven (1 Hz) atrial and ventricular cardiac trabeculae from adult dogs. AP4A (100 microM) alone and after prestimulation with 10 nM isoproterenol reduced force of contraction in atrial preparations by approximately 24%. Moreover, AP4A (100 microM) alone and after prestimulation with 10 nM isoproterenol reduced the force of contraction in ventricular preparations by 29 and 29%, respectively. The negative inotropic effects of AP4A were abolished by the A1-adenosine receptor antagonist 1,3-dipropyl-cyclopentyl-xanthine (DPCPX). In summary, in canine myocardium, AP4A alone and after prestimulation with a beta-adrenoceptor agonist exerts negative inotropic effects, which are probably mediated via A1-adenosine receptors.

[Esophageal cyst--a rare cause of backache]

Cysts of the esophagus are rare mediastinal tumors presenting a large variety of clinical symptoms. Even with modern methods of examination an exact diagnosis is difficult to obtain and often only possible after histological examination. Complications are perforation, or pulmonary, thoracic or esophageal haemorrhage. First choice of therapy is the exstirpation. We report on a 50 year old man with backache and the initial diagnosis of renal colic. Only the magnetic resonance image showed an isolated mediastinal esophageal cyst as the reason. The cyst was removed by thoracotomy. The operation and treatment were without complications. Symptomatology, diagnostical pitfalls and the therapy are described.

Contractility and inhibition of protein phosphatases by cantharidin

1. Cantharidin is a natural defensive toxicant produced by blister beetles. 2. Cantharidin shares structural similarity with highly toxic commercial herbicides (e.g., endothall, endothall anhydride and endothall thioanhydride). 3. Cantharidin inhibits the activity of purified catalytic subunits of serine/threonine protein phosphatases (PP) type 1 and type 2A. 4. Cantharidin increases force of contraction in isolated myocardial and vascular preparations. 5. Cantharidin enhances the phosphorylation state of myocardial and vascular regulatory proteins. 6. Cantharidin is a valuable tool for studying the function of PP in regulatory phosphorylation-dephosphorylation events.

Targeted overexpression of phospholamban to mouse atrium depresses Ca2+ transport and contractility

Phospholamban is a small phosphoprotein regulator of the Ca2+-pump of cardiac sarcoplasmic reticulum. Dephosphorylated phospholamban inhibits the Ca2+-pump and depresses contractility, whereas phosphorylation of phospholamban by cAMP-activated mechanisms relieves this inhibition and increases contractility. In order to better understand the function of phospholamban in living systems, a transgenic mouse model was established employing targeted overexpression of phospholamban to the atrium, which normally expresses low levels of the protein. Overexpression was achieved by fusing the alpha-MHC-promoter or the ANF-promoter to the phospholamban gene. Double transgenic mice were created by mating mice positive for each transgene. In single transgenic lineages, phospholamban was overexpressed four to six-fold in left atrium. In the double transgenic mice, phospholamban was overexpressed eight- to nine-fold. In the three transgenic strains. Ca2+ uptake by the sarcoplasmic reticulum was depressed to 22-30% of control values at low ionized calcium. This depression of Ca2+ uptake was largely reversed by addition of a phospholamban monoclonal antibody. In the atrial muscle strips, the time course of contraction was increased in a concentration-dependent manner by overexpression of phospholamban, whereas the basal developed tension was decreased up to 85% by phospholamban-overexpression. In all transgenic lineages, isoproterenol, a beta-adrenoceptor agonist, reversed the depression of contractility caused by overexpression of phospholamban and significantly shortened time parameters to levels approaching control values. These data demonstrate that overexpression of phospholamban in a mammalian myocardial tissue normally deficient in the protein substantially inhibits basal contractility, and furthermore suggest that in myocardial tissues containing high levels of the protein, phosphorylation of phospholamban can account for many of the positive inotropic and lusitropic effects of beta-adrenergic stimulation.

Muscarinic-cholinoceptor mediated attenuation of phospholamban phosphorylation induced by inhibition of phosphodiesterase in ventricular cardiomyocytes: evidence against a cAMP-dependent effect

In intact guinea pig ventricles, acetylcholine (ACH) has been shown to attenuate the positive inotropic effects of isobutylmethylxanthine (IBMX), a phosphodiesterase inhibitor, by reducing protein phosphorylation without altering cAMP levels. In the present study, we tested the hypothesis that the cAMP-independent inhibitory action of ACH is also evident in isolated cardiomyocytes. cAMP-dependent protein kinase (PKA) activity ratio (-cAMP/+cAMP) and phosphorylation of phospholamban (PLB) were determined in unlabeled and 32P-labeled guinea pig ventricular cardiomyocytes, respectively. IBMX increased PKA activity ratio and phosphorylation of PLB in a dose-dependent manner. When cardiomyocytes were incubated simultaneously with IBMX (0-1 mM) and ACH (2 microM), ACH attenuated PLB phosphorylation stimulated by low concentration (1O-100 microM) but not by high concentrations (> 200 microM) of IBMX. EC50 value for IBMX-induced phosphorylation of PLB was 32 +/- 6 microM and increased nearly 3-fold after addition of ACH while PKA activity ratio remained unchanged. The rank order of cyclic nucleotide derivatives to phosphorylate PLB was 8 bromo-cAMP > dibutyryl cAMP > 8 bromo-cGMP > dibutyryl cGMP. ACH reduced phosphorylation of PLB stimulated by 8 bromo-cAMP. We conclude that in isolated cardiomyocytes (1) ACH inhibits phosphorylation of PLB stimulated by either IBMX or 8 bromo-cAMP and (2) ACH does not lower IBMX-stimulated PKA activity ratio. These effects of ACH on PLB phosphorylation cannot be explained by a reduction in IBMX-stimulated cAMP levels but may involve the activation of protein phosphatases.

Identification and expression of a novel isoform of cAMP response element modulator in the human heart

In end-stage human heart failure, excessive beta-adrenergic stimulation of the cAMP-dependent signaling pathway due to enhanced endogenous catecholamines is hypothesized to contribute to expressional alterations of myocardial regulatory proteins. The cAMP response element modulator (CREM) regulates the transcription of cAMP-responsive genes and might be involved in the regulation of cardiac gene expression. Using the reverse transcription polymerase chain reaction, we identified a novel CREM mRNA, CREM-Ib deltaC-X, in the human heart. Overexpression of CREM-Ib deltaC-X decreased cAMP response element (CRE) -mediated gene transcription in HIT-T15 cells, and this activity was assigned to the part of the sequence encoding putative internally translated proteins. Two of three possible internally translated proteins were immunologically identified in cells overexpressing CREM-Ib deltaC-X tagged with the hemagglutinin epitope of the influenza virus. Both proteins were expressed in bacteria and showed CRE-specific DNA binding, formation of heterodimers with the cAMP response element binding protein (CREB), and inhibition of CREB's binding to the CRE. CREM expression was detected on the mRNA and protein levels in the human heart. We conclude that CREM-Ib deltaC-X generates internally translated repressors of CRE-mediated gene transcription, suggesting the first example for the existence and function of human cardiac CREM.

Long-term beta adrenoceptor-mediated alteration in contractility and expression of phospholamban and sarcoplasmic reticulum Ca(++)-ATPase in mammalian ventricle

We studied the influence of prolonged administration of the beta adrenoceptor agonist isoproterenol on contractile parameters and expression of sarcoplasmic reticulum (SR) Ca(++)-ATPase and phospholamban, genes important for Ca++ uptake into the SR. Isoproterenol (Iso), 0.9% NaCl (Ctr), propranolol (Prop) or Iso plus Prop were administered to rats by subcutaneous infusion with osmotic minipumps for 1, 2, 3, 4, 8, 13 and 26 days, respectively. The positive inotropic effect of Iso was impaired in rats pretreated with Iso in vivo. Iso pretreatment shortened time to peak tension (TPT) by 28%, time of relaxation (RT) by 27% and total contraction time (TCT) by 27% compared with the appropriate controls (day 2). The shortening of time-dependent contractile indices started after 1 day of Iso pretreatment, reached a maximum after 2 days and remained reduced for 4 days. Longer treatment by Iso failed to affect time parameters, whereas the positive inotropic effect of Iso added to the isolated muscles persisted. The shortened contractile time parameters were accompanied by diminished mRNA and protein expression of phospholamban (PLB) and SR-Ca(++)-ATPase (SERCA). The mRNA levels for PLB and SERCA were maximally reduced by 31 +/- 1.3% and 41 +/- 1.4% in the Isopretreated group (2 days) respectively. The reduced mRNA levels were accompanied by reduced levels of the corresponding proteins. It is concluded that altered levels of PLB and SERCA probably account for the noted changes in contractile time parameters in the mammalian heart.

Calcium sensitization as new principle of inotropic therapy in end-stage heart failure?

OBJECTIVE

Due to shortage of donor hearts and increasing waiting-lists of patients with end-stage heart disease, new pharmacological principles for bridging therapies are necessary. The positive inotropic effects of cAMP-increasing drugs (e.g. catecholamines, phosphodiesterase-inhibitors) are diminished in the failing myocardium. Hence, we investigated the usefulness and mechanism of the two calcium sensitizers, levosimendan and CGP 48506 in preparations from end-stage failing human hearts since the exact mechanism of the positive inotropic effects is not yet clearly understood.

METHODS

Failing human hearts which required orthotopic heart transplantation due to idiopathic dilated cardiomyopathy were investigated. Contraction experiments were performed using muscle strips of ventricles. Calcium sensitization was investigated in skinned fibers and phosphodiesterase activity was measured in ventricular homogenate. In addition, cAMP levels were quantified in myocytes from guinea-pig hearts.

RESULTS

In muscle stripes from failing human hearts levosimendan (10 micromol/l) increased the force of contraction only to 112.8 +/- 6.7% of predrug values. In contrast, CGP 48506 increased the force of contraction to 311 +/- 59% of predrug values at 100 micromol/l. The time to peak tension and time of relaxation were increased to 175 +/- 4% and 205 +/- 15% of control levels at 100 micromol/l. Skinned fibers from failing human hearts were sensitized to calcium with an EC50 of 10 micromol/l. Other mechanisms of action were excluded since CGP 48506 affected neither the activity of phosphodiesterase isoenzymes I-IV in failing human hearts, nor cAMP levels in guinea-pig cardiomyocytes. On the other hand, levosimendan (1 micromol/l) increased cAMP content from 6.3 +/- 0.3 to 8.1 +/- 0.3 pmol/mg protein.

CONCLUSION

CGP 48506 is an inotropic agent with calcium-sensitizing properties in the human heart, that is devoid of inhibitory activity on human cardiac phosphodiesterase isoenzymes. It offers, therefore, a new form of positive inotropic therapy that can be useful for the bridging treatment of heart failure before transplantation. On the other hand, levosimendan is a calcium sensitizer showing less-effective inotropic effects accompanied by increased cAMP levels.

[The effect of the primary operation on reoperations on the thyroid gland]

The authors analyze the possibility to reduce the number of reoperations of the thyroid gland, based on a group of thyroid operations performed at the Surgical Clinic of the Second Medical Faculty Charles University and Faculty Hospital Motol during the 22-year period from 1975-1997. 507 reoperations from a total number of 4501 thyroid operations amount to 11.3%. In the authors opinion correct indication of the operation is most important as well as the correct extent and technique of the primary operation. The achieved results are except for unilateral temporary lesions of the NLR comparable with primary operations.

Deferoxamine blocks interactions of fluoride and carbachol in isolated mammalian cardiac preparations

In papillary muscles, carbachol reduced the positive inotropic effects of isoprenaline (10 nmol/l). The negative inotropic effects of carbachol in isoprenaline-stimulated guinea pig papillary muscles were attenuated by additionally applied sodium fluoride (3 mmol/l). These effects of sodium fluoride were blocked by deferoxamine (200 micromol/l). In guinea pig left atria, sodium fluoride alone greatly reduced force of contraction. These effects in atria were blocked by 200 micromol/l deferoxamine, and positive inotropic effects of sodium fluoride were observed. It is suggested that the cardiac effects of muscarinic M2 receptor agonists in the ventricle involve, at least in part, the activation of phosphatases which are blocked by fluoride and reactivated by deferoxamine.

Postnatal changes in contractile time parameters, calcium regulatory proteins, and phosphatases

Compared with isolated electrically driven neonatal ventricular preparations, the total time of contraction, the time to peak tension, and the time of relaxation were decreased to approximately 50% in adult ventricular preparations. The expression of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) was increased to 133% at the protein level and to 154% at the mRNA level in adult vs. neonatal ventricular preparations, whereas phospholamban was unchanged at both the protein and mRNA levels. Moreover, Ca2+ uptake was increased to 180% in adult vs. neonatal ventricular preparations. Phospholamban phosphorylation was enhanced in adult vs. neonatal ventricular preparations. In adult ventricular preparations, phosphatase activity was reduced to 53% of neonatal preparations, the protein levels of the immunologically detectable catalytic subunits of protein phosphatase types 1 and 2A were reduced to 28 and 61% of neonatal preparations, respectively, and the mRNA levels of type 1alpha, 1beta, 1gamma, 2Aalpha, and 2Abeta phosphatase isoforms were decreased to 69, 68, 54, 67, and 63%, respectively. We conclude that in the adult rat heart, the shortened time parameters of contraction can be explained by an elevated expression of SERCA. In addition, an increased phosphorylation state of phospholamban due to reduced phosphatase activity may be involved.

Octreotide in the management of diarrhea induced by graft versus host disease

PURPOSE/OBJECTIVES

To evaluate the potential benefit of the somatostatin analogue, octreotide, for the management of diarrhea induced by graft versus host disease (GVHD).

DATA SOURCE

Pilot clinical trial involving 21 patients undergoing allogeneic transplant with positive histologic or radiographic evidence of GVHD of the gastrointestinal tract who failed antidiarrheal therapy with loperamide.

DATA SYNTHESIS

A complete response, defined as resolution of diarrhea, was seen in 71% of trial participants (15 of 21 patients). At the dose and scheduling used (500 mcg i.v. three times daily for a median of seven consecutive days), octreotide was extremely well tolerated in all patients.

CONCLUSIONS

In this pilot study, octreotide treatment was effective in reducing the amount of diarrhea in patients with acute GVHD. The data suggest that patients receiving octreotide early in the course of the diarrhea experienced more benefit than patients with persistent diarrhea prior to receiving octreotide. The demonstrated safety and efficacy of octreotide in this patient population support further investigation of this therapeutic strategy for GVHD-induced diarrhea. A randomized, controlled, clinical trial of octreotide versus loperamide for the initial treatment of GVHD-induced diarrhea is warranted.

IMPLICATIONS FOR NURSING PRACTICE

Octreotide should be administered early in the course of GVHD as soon as onset of diarrhea is noted and should be discontinued as soon as diarrhea resolves to avoid constipation and the potential development of an ileus. Because response to the drug usually occurs quickly, maintaining treatment for additional days or weeks is unnecessary. If a benefit is not seen in four to seven days, continuing octreotide therapy is neither cost-effective nor prudent.

Receptor mechanisms involved in the 5-HT-induced inotropic action in the rat isolated atrium

1. The effects of 5-hydroxytryptamine (5-HT) in rat cardiac preparations were studied. 5-HT up to 10 microM failed to affect contractility in papillary muscles. However, in electrically driven (1 Hz) left atria 5-HT exerted a positive inotropic effect that started at 1 microM and attained its maximum at 10 microM (312+/-50% of predrug value, n=8). 2. 5-HT 10 microM stimulated the content of inositol-1,4,5-trisphosphate but not of cyclic AMP in rat left atria. 3. Plasma and serum levels of 5-HT amounted to about 0.3 microM and 15 microM, respectively. 4. The selective 5-HT4 receptor antagonists GR 125487 (10 nM and 1 microM) and SB 203186 (1 microM) did not attenuate the positive inotropic effect of 5-HT in rat left atria. In contrast, the 5-HT2 receptor antagonist ketanserin (5 nM, 50 nM, 1 microM) resulted in a concentration-dependent diminution of the positive inotropic effect of 5-HT in rat left atria. 5. Reverse transcriptase polymerase chain reaction with specific primers detected mRNA of the 5-HT2A receptor in rat atria and ventricles, while expression of the 5-HT4 receptor was confined to atria. 6. It is suggested that the positive inotropic effect of 5-HT in electrically driven rat left atria is mediated by ketanserin-sensitive 5-HT2A receptors and not through 5-HT4 receptors.

Expression of calcium regulatory proteins in short-term hibernation and stunning in the in situ porcine heart

BACKGROUND

Myocardial hibernation and stunning are characterised by a reversible contractile dysfunction during and after ischaemia, respectively. Calcium homeostasis might be disturbed in hibernation and stunning due to altered expression of cardiac proteins involved in calcium handling.

METHODS

In enflurane-anaesthetised swine the coronary blood flow through the left anterior descending coronary artery was decreased to reduce regional contractile function (microsonometry) by approximately 50%. In transmural biopsies obtained during ischaemia and reperfusion creatine phosphate as well as the expression of sarcoplasmic reticulum calcium ATPase (SERCA), phospholamban (PLB), calsequestrin (CSQ), and troponin inhibitor (TnI) were determined.

RESULTS

During ischaemia creatine phosphate, after an initial reduction, recovered back to control values, and necrosis was absent (hibernation). After 90 min of ischaemia the myocardium was reperfused for 120 min but regional contractile function continued to be depressed (stunning). PLB, SERCA, CSQ, and TnI proteins were unchanged during ischaemia as well as reperfusion. Likewise, levels of PLB and SERCA mRNAs were unchanged.

CONCLUSION

It is concluded that other mechanisms than altered expression of these regulating proteins underlie the contractile dysfunction observed during acute ischaemia, short-term hibernation and stunning.

The mechanism of action of cantharidin in smooth muscle

1. The aim of this study was to investigate the mechanism(s) of the vasoconstrictor effect of cantharidin in bovine preparations. 2. Catalytic subunits of protein phosphatase type 1 (PP 1) and type 2A (PP 2A) were immunologically identified in coronary arteries, isolated smooth muscle cells and ventricular myocardium. 3. The mRNAs coding for catalytic subunits of PP 1alpha, PP 1beta and PP 2Aalpha were identified by hybridization with specific cDNA-probes in total RNA from coronary arteries, isolated smooth muscle cells and ventricles. 4. The activities of catalytic subunits of PP 1 and PP 2A separated by column chromatography from coronary arteries, isolated smooth muscle cells and ventricles were inhibited by cantharidin in a concentration-dependent manner. 5. Cantharidin increased the phosphorylation state of smooth muscle proteins including the regulatory light chains of myosin in 32P-labelled intact smooth muscle cells in a concentration-dependent manner. 6. Cantharidin did not affect cytosolic calcium concentrations in aortic smooth muscle cells. 7. It is suggested that cantharidin contracts smooth muscle preparations by increasing the phosphorylation state of regulatory proteins due to inhibition of phosphatase activities. Thus, cantharidin might be a useful tool to study the function of phosphatases in smooth muscle.

Parametric amplification of a coherent light wave in photorefractive BaTiO(3) by a single pump beam

We demonstrate a new method of light amplification based on forward four-wave mixing in photorefractive BaTiO(3). A single pump beam of combined (ordinary and extraordinary) polarization can be used for an efficient cw amplification of a signal wave with slightly shifted temporal frequency. A signal wave with an initial power of less than 1 nW is amplified ~100 times in a 3.2-mm-thick sample.

Characterization of biochemical effects of CGS 21680C, an A2-adenosine receptor agonist, in the mammalian ventricle

Effects of a putative A2-adenosine receptor agonist 2-[(p-2-carboxyethyl)-phenethylamino]-5'-N-ethyl-carboxamide-adeno sine (CGS 21680C) on force of contraction, protein phosphorylation, cyclic adenosine monophosphate (cAMP) content, and the activity of phosphodiesterase (PDE) isoenzymes in guinea pig ventricular (GPV) preparations were studied. CGS 21680C (1-100 microM) did not affect force of contraction in isolated electrically driven papillary muscles and was ineffective in increasing phosphorylation of phospholamban (PLB) and the inhibitory subunit of troponin (TnI) in [32P]-labeled GPV cardiomyocytes. However, under the same conditions, CGS 21680C (10 microM) increased cAMP content from 4.3 +/- 0.2 to 13.0 +/- 0.6 pmol/mg protein, and this effect was completely abolished by A2-adenosine receptor antagonist 9-chloro-2-(2-furanyl)-5,6-dihydro-1,2,4-triazolo-(1,5-c)quinazolin++ +-5-imine (CGS 15943A). CGS 21680C (10 microM) inhibited PDE isoenzymes I, II, III, IV by 7.0, 8.3, 4.7, and 23.2%, respectively. Similarly, rolipram (100 microM), a selective PDE IV inhibitor, increased cAMP content from 4.4 +/- 0.3 to 7.2 +/- 0.3 pmol/mg protein without affecting the phosphorylation state of PLB and TnI. We conclude that CGS 21680C increases cAMP content in GPV cardiomyocytes by activation of adenylyl cyclase or in part by inhibition of PDE IV activity. The increase in cAMP content by CGS 21680C or rolipram is ineffective in increasing phosphorylation of PLB and TnI. These results support the concept of compartments for cAMP or protein kinase A or both in cardiomyocytes that are not coupled to phosphorylation and contractility.