Otologic disease trends in Japan post-COVID-19 outbreak: A retrospective time-series analysis

OBJECTIVE

To evaluate the potential impact of coronavirus disease 2019 (COVID-19) and vaccinations on otologic diseases, including facial nerve paralysis (including Ramsay Hunt syndrome), vestibular neuritis, sudden sensorineural hearing loss, and Meniere's disease.

METHODS

In this retrospective study, we conducted a time-series analysis employing a causal impact algorithm on a large-scale inpatient database in Japan. We compared the actual number of hospitalized patients with otologic diseases to two predictions: one without any covariates and another with a covariate accounting for the reduction in the number of hospitalized patients due to lockdown measures. Additionally, we performed Granger causality tests to ensure the robustness of our findings.

RESULTS

No significant increase was noted in the number of hospitalized patients with otologic diseases following the onset of the COVID-19 pandemic in the causal impact analysis. Similarly, no notable surge was observed in hospitalizations for these diseases following the introduction of the COVID-19 vaccine. The Granger causality tests results aligned with the causal impact analysis findings.

CONCLUSION

Our findings indicate that COVID-19 and vaccinations had minimal discernible effects on hospitalization of patients with otologic diseases, suggesting that otologic diseases may not be significantly impacted by COVID-19 and vaccinations, which could have implications for public health policies and the allocation of healthcare resources during a pandemic. Further research and monitoring of long-term effects are warranted to validate these findings and guide healthcare decision-making.

[Acute onset of tuberculous meningoencephalitis presenting with symmetric linear lesions in the bilateral thalamus: a case report]

A 18-year-old woman was admitted to our hospital because of high fever and headache. Nuchal stiffness was present, and a CSF examination showed lymphocyte-domonant pleocytosis and a decreased level of glucose. Although antibiotics, aciclovir and an antimycotic drug were administered, disturbance of consciousness, involuntary movements, and pyramidal tract signs appeared. Soon after the medications were changed to antituberculous medicines, the meningoencephalitis started to subside, and was finally cured. Judging from the clinical findings, the CSF findings, the effectiveness of antituberculous medicines, an elevated ADA level in CSF, and positive conversion in tuberculin tests, the final diagnosis was made as tuberculous meningoencephalitis. At the severest stage of the disease, a brain MRI showed symmetric, linear lesions without the effect of Gd-enhancement in the bilateral thalamus, which thereafter disappeared along with the healing of the illness. From all these things, we conclude that thalamic and other parenchymal lesions should be kept in mind in case of acute tuberculous meningoencephalitis.

Effect of initial tumor stage on patient follow-up after potentially curative surgery for cutaneous melanoma

The optimal follow-up strategy after completion of therapy for melanoma is not known. We evaluated the effect of TNM stage on the self-reported surveillance strategies employed by practicing plastic surgeons caring for otherwise healthy patients subjected to potentially curative treatment for cutaneous melanoma. Hypothetical patient profiles and a detailed questionnaire based on these profiles were mailed to a random sample (N=3,032) of the 4,320 members of the American Society of Plastic and Reconstructive Surgeons. The effect of TNM stage on the surveillance strategies chosen was analyzed by repeated-measures ANOVA. There were 1,142 responses to the 3,032 surveys; 395 were evaluable. Plastic surgeons often do not provide postoperative follow-up themselves; this was the most frequent reason for non-evaluability. Surveillance of patients after resection of melanoma relies most heavily on office visits, chest X-ray, CBC, and liver function tests. All other surveillance modalities are used infrequently. Most respondents modify their surveillance practices slightly according to the patient's initial TNM stage. Most commonly used modalities are employed significantly more frequently with increasing TNM stage. This effect persists through ten years of follow-up, but the differences across stages are tiny. We conclude that most plastic surgeons performing surveillance after potentially curative surgery in otherwise healthy patients with melanoma use similar follow-up strategies for patients of all TNM stages. These data permit the rational design of a controlled clinical trial of high-intensity vs. low-intensity follow-up.

Current practice of patient follow-up after potentially curative resection of cutaneous melanoma

Follow-up care for patients who have undergone potentially curative resection of cutaneous melanoma varies widely among physicians, and the underlying rationale has not been assessed. To quantify current practice patterns and to discern motivation, a custom-designed questionnaire was mailed to U.S. and non-U.S. surgeons, all of whom were members of the American Society of Plastic and Reconstructive Surgeons (ASPRS). Surveys were mailed to 3,032 ASPRS members, chosen randomly from a total of 4,320 members. Of the 1,142 questionnaires that were returned, 395 were evaluable. Nonevaluability was usually due to lack of melanoma patients receiving follow-up in the surgeons' practices. Surveillance of patients after resection of melanoma relies most heavily on office visit, chest x-ray, complete blood count, and liver function tests. There was surprisingly little influence of elective node dissection on follow-up practices. Imaging tests such as computed tomography, magnetic resonance imaging, and position emission tomography scan were rarely employed. Surveillance is motivated by many factors, particularly early detection of recurrence of the index melanoma and second primary melanomas. This survey provides information regarding current follow-up strategies recommended by ASPRS surgeons after potentially curative resection of cutaneous melanoma. There is considerable variation in surveillance intensity and in motivation among practitioners, thus representing a lack of consensus.

Protective effect of gamma-glutamylcysteinylethyl ester on dysfunction of the selenium-deficient rat heart

We investigated the protective effect of intracellular GSH against cardiac dysfunction in selenium (Se)-deficient neonatal rats and cultured fetal rat myocytes. A Se-deficient diet with or without daily subcutaneous injections of gamma-glutamylcysteinylethyl ester (gammay-GCE) (a membrane-permeating GSH precursor) was given to rats from gestation day 4 via the dam to postnatal day 14. Se deficiency induced a 62% incidence of electrocardiographic abnormalities such as sinus arrhythmias or extrasystole, a 63% reduction in dP/dt in the left ventricle, and an increase in thiobarbituric acid reacting substances (TBARS), but no ultrastructural cardiac lesions were observed. Administration of gamma-GCE increased the intracellular GSH concentration ([GSH]i) of both neonatal rat hearts and cultured fetal rat cardiac myocytes. gamma-GCE-like sodium selenite prevented the cardiac dysfunction and the TBARS increment. gamma-GCE also prevented H2O2 toxicity in the cultured myocytes. The Vmax, but not the Km, for GSH of Se-dependent GSH peroxidase (Se-Gpx) activity in Se-deficient rat heart homogenates was one-third that of normal rat heart homogenates. Although gamma-GCE did not affect the Se-Gpx Vmax and Km for GSH, it did induce a substantial and significant increase in [GSH]i, which was postulated to increase the velocity of H2O2 decomposition by Se-Gpx activity 1.6-fold. These data suggest that the increase in [GSH]i may have played a role in preventing the TBARS increase and cardiac dysfunction in Se-deficient rats.

Protective effect of coenzyme Q10 on cultured skeletal muscle cell injury induced by continuous electric field stimulation

The protective effect of coenzyme Q10 (CoQ10) on continuous electric field stimulation-induced muscular injury was investigated in cultured cells established from neonatal rat femoral muscles. After cultivation for 9 days, skeletal muscle cells contracted and relaxed rhythmically for 4 hr in response to continuous electric field stimulation (power, 5 V; duration, 5 msec; amplitude, 3 Hz). After the onset of the stimulation, lactate and lactate dehydrogenase (LDH) release and intracellular Ca2+ contents ([Ca2+]i) at relaxation increased gradually. In contrast, the intracellular ATP contents decreased. The addition of 5 microM CoQ10, but not alpha-tocopherol and radical scavengers, to the culture medium protected the cells against these biochemical changes after the stimulation. Verapamil, an inhibitor of Ca2+ channels, also attenuated the increase in [Ca2+]i at relaxation and LDH. These results suggested that one of the causal mechanisms of muscular injury is an increase in [Ca2+]i due to the excess entry of extracellular Ca2+, and that CoQ10 can protect skeletal muscle cells against such undesirable biochemical changes.

Detachment of cultured cells from the substratum induced by the neutrophil-derived oxidant NH2Cl: synergistic role of phosphotyrosine and intracellular Ca2+ concentration

The neutrophil-derived, membrane-permeating oxidant, NH2Cl, (but not the non-membrane-permeating chloramine, taurine-NHCl) induced detachment of fetal mouse cardiac myocytes and other cell types (fibroblasts, epithelial cells, and endothelial cells) from the culture dish, concomitant with cell shrinkage ("peeling off"). Stimulated human neutrophils also induced peeling off of cultured mouse cardiac myocytes when the latter were pretreated with inhibitors of .OH and elastase. Immunofluorescence microscopy revealed that the NH2Cl-induced peeling off of WI-38 fibroblasts is accompanied by disorganization of integrin alpha 5 beta 1, vinculin, stress fibers, and phosphotyrosine (p-Tyr)-containing proteins. Decrease in the content of the p-Tyr-containing proteins of the NH2Cl-treated cells was analyzed by immunoblotting techniques. Coating of fibronectin on the culture dish prevented both NH2Cl-induced peeling off and a decrease in p-Tyr content. Preincubation with a protein-tyrosine phosphatase inhibitor, sodium orthovanadate (Na3VO4), also prevented NH2Cl-induced peeling off, suggesting that dephosphorylation of p-Tyr is necessary for peeling off. NH2Cl-induced peeling off was accompanied by an increase in intracellular Ca2+ concentration ([Ca2+]i) in mouse cardiac myocytes and WI-38 fibroblasts. The absence of extracellular Ca2+ prevented both NH2Cl-induced peeling off and increased [Ca2+]i, both of which did occur on subsequent incubation of the cells in Ca2+-containing medium. These observations suggest that an increase in [Ca2+]i is also necessary for peeling off. Depletion of microsomal and cytosolic Ca2+ by incubation with the microsomal Ca2+-ATPase inhibitor 2',5'-di(tert-butyl)-1,4-benzohydroquinone (BHQ) plus EGTA prevented both NH2Cl-induced increases in [Ca2+]i and peeling off. Direct inhibition of microsomal Ca2+ pump activity by NH2Cl may participate in the NH2Cl-induced [Ca2+]i increment. A combination of p-Tyr dephosphorylation by genistein (an inhibitor of tyrosine kinase) and an increase in [Ca2+]i by BHQ could also induce peeling off. All these observations suggest a synergism between p-Tyr dephosphorylation and increased [Ca2+]i in NH2Cl-induced peeling off.

Melittin cardiotoxicity in cultured mouse cardiac myocytes and its correlation with calcium overload

Venom from the honey bee Apis mellifera induces cardiovascular dysfunction. We studied which constituent(s) of the venom induces cardiotoxicity and how, using cultured cardiac myocytes from mouse fetuses. Among the venom constituents, only melittin caused contractile and morphological effects; other peptides, such as apamin and mastparan; enzymes, such as phospholipase A2; and low-molecular-weight compounds, such as histamine and dopamine, did not. Treatment with 4.5 micrograms/ml melittin, which accounts for about half the dry weight of the venom, induced the same cardiotoxic effects as treatment with 9.0 micrograms/ml whole venom; these effects were a transient increase in the spontaneous beating rate, then a decrease, then cessation of beating, and finally, morphological degeneration. The cardiotoxicity of whole bee venom was completely destroyed by pretreatment of the venom with antimelittin antibody. These results suggest that bee venom cardiotoxicity is attributable to melittin. When spontaneous beating ceased following the addition of melittin or whole venom, an increase in systolic [Ca2+]i, was observed. On further incubation with melittin or bee venom, morphological injury, such as balloon degeneration, occurred concomitant with a further increase in the [Ca2+]i. An extracellular Ca2+ concentration of more than 10(-6) M was necessary for morphological injury. Melittin depolarized the maximum diastolic potentials, inhibited the generation of action potentials, and induced an increase in [Na+]i. Cells were protected against the melittin-induced increase in [Ca2+]i by pretreatment with bepridil, an inhibitor of Na(+)-Ca2+ exchange, but not by Ca2+ channel blockers such as verapamil. These observations suggest that the melittin-induced increase in [Ca2+]i was due to entry of extracellular Ca2+ via the sarcolemmal Na(+)-Ca+ exchange system.

Long-term observation of a case of pulmonary arteriovenous fistula with pulmonary hypertension

A case of pulmonary arteriovenous fistula (PAVF) with pulmonary hypertension (PH) occurring in an adult woman is described. Resection of PAVF was not performed and she has been followed up for 5 years, receiving repeated right cardiac catheterization. We discuss the causal relationship of PH and the development of PAVF.

Polymorphonuclear leukocytes-induced injury in hypoxic cardiac myocytes

Growing evidence suggests that free radicals derived from polymorphonuclear leukocytes (PMNs) play an important role in myocardial ischemia-reperfusion injury. To elucidate the cellular mechanism by which activated PMNs exacerbate ischemic myocardial damage, we investigated the extent of cell injury, assessed by the morphological deterioration, free radical generation, and lipid peroxidation in mouse embryo myocardial cells coincubated with activated PMNs. The generation of PMN-derived free radicals was related to the extent of myocardial cell injury. When myocardial cell sheets were subjected to hypoxia and glucose-free media, myocardial cells were injured (cristalysis in the mitochondria and disruption of the sarcolemma) after adding various PMN activators, and the injury extended to the adjacent cells. Chemiluminescent emission and production of thiobarbituric acid-reactive substances in the coincubated cells increased markedly compared with myocardial cells or PMNs alone. The augmented lipid peroxidation coincided with the progression of myocardial cell injury. Catalase inhibited the myocardial cell injury by 52%, the chemiluminescence by 46%, and lipid peroxidation by 50%, whereas superoxide dismutase exhibited less pronounced inhibition. These results indicate that a chain reaction of lipid peroxidation in myocardial cells induced by PMN-derived free radicals closely correlates with membrane damage and contributes to the propagation of irreversible myocardial cell damage.

KN-62, a specific Ca++/calmodulin-dependent protein kinase inhibitor, reversibly depresses the rate of beating of cultured fetal mouse cardiac myocytes

Effects of KN-62 (1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4- phenylpiperazine), a specific Ca++/calmodulin (CaM)-dependent protein kinase inhibitor, were examined on the rate of spontaneous beating and the intracellular Ca++ transient of cultured myocytes from fetal mouse ventricle. KN-62 depressed the rate of beating in a dose-dependent fashion. Spontaneous beating ceased 10 min after the administration of 1 microM KN-62 and recovered gradually after washing with cultured medium. Addition of KN-04 [N-(1-1[P-(5-isoquinolinsulfonyl)benzyl]-2-(4- phenylpiperazinyl)ethyl)-5-isoquinolinsulfonamide; 1 microM], an analog of KN-62, did not change the rate of beating. In the experiment using an intracellular Ca++ fluorescence indicator, fluo-3, KN-62 depressed the fluo-3 intensity at a systolic phase. The kinase activity to syntide-2 of Ca++/CaM kinase II purified from the rabbit heart was inhibited by KN-62, but not by KN-04. Addition of KN-62 inhibited the phosphorylation of phospholamban by Ca++/CaM kinase II in a dose-dependent manner. KN-62 depressed the Ca(++)-pumping ATPase activity in the presence of Ca++ and CaM by 32%. These findings indicate that Ca++/CaM kinase II changes an intracellular Ca++ transient and modulates the rate of beating at least in part.

Metabolic coupling of glutathione between mouse and quail cardiac myocytes and its protective role against oxidative stress

Cultured quail myocytes were much more resistant to H2O2 toxicity than cultured mouse myocytes. The intracellular concentration of glutathione ([GSH]i) and the activity of gamma-glutamylcysteine synthetase (gamma-GCS) in quail heart cells were about five and three times higher, respectively, than in mouse heart cells, although catalase and glutathione peroxidase (GSHpx) activity was similar in both. Preloading of gamma-glutamylcysteine monoethyl ester (gamma-GCE), a membrane-permeating GSH precursor, increased the H2O2 resistance of cultured mouse myocytes. These observations suggest that the high [GSH]i and the high activity of gamma-GCS in quail myocytes are responsible for their high resistance to H2O2. Both H2O2 sensitivity and [GSH]i of mosaic sheets composed of equal amounts of mouse and quail myocytes approximated those of sheets composed entirely of quail myocytes. From these observations, it is hypothesized that GSH was transferred from quail myocytes to mouse myocytes, probably through gap junctions between them, and that quail myocytes resynthesized GSH by a feedback mechanism, thus maintaining their intracellular GSH levels. When the fluorescent dye lucifer yellow was injected into a beating quail myocyte in a mosaic sheet, it spread to neighboring mouse myocytes but not to neighboring L cells (a cell line derived from mouse connective tissue). These observations indicate that existence of gap junctions in the region of cell contact between mouse and quail myocytes but not between quail myocytes and L cells. When quail myocytes preloaded with [3H]gamma-GCE were cocultured with mouse myocytes and L cells, the radioactivity was transmitted to neighboring mouse myocytes but not L cells. These observations show that GSH and/or its precursors can be transmitted from quail myocytes to mouse myocytes through gap junctions and that this can protect mouse myocytes from H2O2 toxicity. Mouse myocyte sheets composed of 10(4) cells or more showed higher resistance to H2O2 toxicity than single isolated mouse myocytes. Metabolic coupling of GSH between myocytes may contribute at least in part to this high resistance of the cell sheets.

Contractile and morphological impairment of cultured fetal mouse myocytes induced by oxygen radicals and oxidants. Correlation with intracellular Ca2+ concentration

There is evidence that reperfusion injury of cardiac tissue may be caused by the generation of oxygen-derived free radicals and oxidants and by the induction of intracellular calcium overload, although the relation between these two mechanisms of injury is uncertain. In addition, the relation between the types of cellular injury and specific active species is unclear. In an attempt to resolve these problems, we investigated the effects of oxygen radicals and oxidants, which are purportedly generated during reperfusion after prolonged ischemia, and various antioxidants on contractility and morphology of cultured fetal mouse cardiac myocytes. Xanthine oxidase in the presence of xanthine, H2O2, HOCl, and NH2Cl induced cessation of spontaneous beating followed by cessation of electrical stimulation-elicited beating but did not induce an increase in [Ca2+]i. After prolonged incubation with xanthine oxidase + xanthine and H2O2, the cardiac myocytes showed morphological degeneration (at least 80% of the cells developed hypercontraction) with a concomitant increase in [Ca2+]i. These observations suggest that contractile impairment does not result in an increase of [Ca2+]i, but hypercontraction does. Catalase, but not superoxide dismutase, protected the cultured cardiac myocytes against xanthine oxidase + xanthine- and H2O2-induced contractile and morphological impairment. In the light of this observation, we hypothesize that the superoxide anion is not responsible for these types of impairment. Addition of dimethylthiourea (an .OH scavenger) and intracellular preloading with deferoxamine (an iron chelator) protected the myocytes against H2O2-induced contractile and morphological damage, but intracellular preloading with iron enhanced it. These observations led us to hypothesize that intracellularly generated .OH may be a mediator of H2O2-induced injury to cultured cardiac myocytes. In addition, we observed that H2O2 itself induced cessation of spontaneous but not electrical stimulation-elicited beating.

Cardiostimulatory action of coenzyme Q homologues on cultured myocardial cells and their biochemical mechanisms

The effect of coenzyme Q (CoQ) homologues on the beating of myocardial cells was investigated in cultured cell sheets from mouse fetuses and quail embryos. Myocardial cell sheets grown in Eagle's minimum essential medium with fetal bovine serum showed very weak and irregular beating when this serum was removed from the medium. However, the depressed beating rate and amplitude recovered almost completely within a few minutes by adding CoQ10 to the medium, and the effect of CoQ10 continued over 1 h. CoQ9 showed a cardiostimulatory effect similar to that of CoQ10, but CoQ8 and CoQ7 showed almost no effect. Short homologues (less than CoQ4) inhibited the beating of cell sheets. The cardiostimulatory effect of CoQ10 was not blocked by atenolol, a selective beta-blocker. In addition, CoQ10 stimulated the formation of ATP, not cAMP. CoQ0 and CoQ3 inhibited beating rates by inhibiting ATP formation. In conclusion, only native CoQ homologues having a nona- or decaprenyl group showed a cardiostimulatory effect on cultured myocardial cells, probably by stimulating mitochondrial ATP formation.

A novel ubiquinone reductase activity in rat cytosol

Ubiquinone (UQ) reductase activity which reduces UQ to ubiquinol (UQH2) in rat tissues was roughly proportional to the UQH2/total UQ ratio in respective tissues. The highest activity was found in the liver, showing the highest UQH2/total UQ ratio. A greater part of liver UQ reductase activity was located in the cytosol. Within a week, the liver UQ reductase activity decreased by 80% even at -20 degrees C. The DT-diaphorase activity was stable. UQ reductase required NADPH as the hydrogen donor and was not inhibited by a less than 1 microM concentration of dicoumarol. There was no stimulation of UQ reductase in the presence of bovine serum albumin nor in Triton X-100. Yet, both stimulated DT-diaphorase. As a result, UQ reductase appeared to be a novel NADPH-UQ oxidoreductase and responsible for the UQ redox state in liver.

Mechanism of intrahippocampal neostigmine-induced hyperglycemia in fed rats

We previously reported that the injection of neostigmine, an acetylcholine esterase inhibitor, into the dorsal hippocampus produced hepatic venous plasma hyperglycemia associated with an increase of epinephrine and glucagon in anesthetized fed rats. To evaluate the relative contribution of these glucoregulatory hormones and the nervous system to the net hyperglycemic response, we unilaterally injected neostigmine (5 x 10(-8) mol) into the dorsal hippocampus in the following groups of rats: intact rats with bilateral adrenalectomy to eliminate the action of epinephrine, and rats receiving a constant infusion of somatostatin and insulin to prevent the glucagon response and to maintain the basal insulin level. Hepatic venous plasma levels of glucose, immunoreactive glucagon, immunoreactive insulin, epinephrine, and norepinephrine were determined. The area under the glucose curve during the 120-min period following the injection of neostigmine was compared between groups. The areas under the glucose curve for rats receiving somatostatin and insulin, adrenalectomy rats, and adrenalectomy rats receiving somatostatin and insulin were, respectively, 82, 31, and 61% of that for intact rats. The fashion of hippocampal stimulated hyperglycemia with neostigmine was similar to that after injection of neostigmine into the third cerebral ventricle. Therefore, we investigated hyperglycemia in rats with lesions of ventromedial hypothalamus and found that the response to hippocampal neostigmine was significantly inhibited by the hypothalamic lesion. These findings suggest that the glucoregulatory hippocampal activity evoked by neostigmine may be transmitted to peripheral organs via the ventromedial hypothalamus.

Reciprocal changes of plasma glucose and ketone bodies in fasted and acutely diabetic rats after CNS stimulation

To assess the effect of chemical stimulation of the central nervous system (CNS) on ketogenesis, we injected neostigmine (5 x 10(-8)mol) into the third cerebral ventricle in normal rats fasted for 48 h and fed rats with diabetes induced by streptozotocin (STZ, 80 mg/kg). The hepatic venous plasma levels of ketone bodies (3-hydroxybutyrate and acetoacetate), free fatty acids (FFA), and glucose were measured for 120 min after the injection of neostigmine under pentobarbital anesthesia. In the normal rats, plasma glucose levels were significantly increased but neither ketone bodies nor FFA were affected by CNS stimulation with neostigmine. In contrast the plasma levels of ketone bodies and FFA were significantly increased in STZ-diabetic rats, while glucose levels remained unchanged. The intravenous infusion of somatostatin (1.0 microgram/kg/min) suppressed the increase in plasma ketone bodies following CNS stimulation in STZ-diabetic rats. These findings suggest that CNS stimulation with neostigmine may accelerate ketogenesis by promoting the lipolysis, which may be induced by glucagon, in fed diabetic rats but not in normal fasted rats.

Properties of a hemolysin related to the thermostable direct hemolysin produced by a Kanagawa phenomenon negative, clinical isolate of Vibrio parahaemolyticus

A hemolytic toxin (Vp-TRH) produced by a Kanagawa phenomenon negative, clinical isolate of Vibrio parahaemolyticus was further characterized. The purified Vp-TRH showed various biological activities, such as fluid accumulation in rabbit ileal loops, increase of rabbit skin vascular permeability, and cardiotoxicity on cultured myocardial cells, all of which are essentially similar to the activities found with thermostable direct hemolysin (Vp-TDH), a pathogenic toxin produced by Kanagawa phenomenon positive V. parahaemolyticus. Immunological similarities of Vp-TRH not only to Vp-TDH but also to hemolytic toxins produced by Vibrio hollisae and Vibrio cholerae non-O1, both of which are also enteropathogens closely related to V. parahaemolyticus, were demonstrated. The amino acid composition and sequence of N-terminal amino acids of Vp-TRH were determined. These results suggest that Vp-TRH has biological and immunological characters similar to Vp-TDH, although they are distinct molecules.

5-Hydroxytryptamine induces phospholipase C-mediated hydrolysis of phosphoinositides through 5-hydroxytryptamine-2 receptors in cultured fetal mouse ventricular myocytes

5-Hydroxytryptamine (5-HT) stimulates the rate and force of cardiac contraction. However, the molecular mechanisms of 5-HT actions on the heart are unknown. We examined effects of 5-HT on phospholipase C-mediated hydrolysis of phosphoinositides and its regulation in cultured fetal mouse ventricular myocytes labeled with [3H]inositol. Accumulation of inositol monophosphate, inositol bisphosphate, and inositol trisphosphate was assessed after stimulation with 5-HT, catecholamines, and AlF4-. Inositol bisphosphate and trisphosphate reached a peak at 15 minutes by 5-HT stimulation and at 30 minutes by AlF4- stimulation. Inositol monophosphate accumulated linearly for at least 30 minutes in the presence of LiCl. The 5-HT effect was dose dependent, and the threshold concentration was 0.1 microM with the half-maximum effective concentration of 1 microM. Ketanserin in nanomolar concentrations inhibited the phospholipase C reaction by 100 microM 5-HT with the half-maximum inhibitory concentration of 0.5 nM. Pertussis toxin (100-1,000 ng/ml) did not influence the phospholipase C reaction by 5-HT, but it partially inhibited the reaction by AlF4-. Protein kinase C-activating phorbol esters like 12-O-tetradecanoylphorbol 13-acetate (TPA) and phorbol 12,13-dibutyrate, but not 4 alpha-phorbol 12,13-didecanoate, which is inactive for protein kinase C, completely inhibited the reaction by 5-HT; TPA showed 30% inhibition on the reaction by AlF4-. The magnitude of accumulated inositol phosphates by AlF4- was at least several times greater than that by 5-HT. Norepinephrine- and epinephrine-stimulated phospholipase C reactions were completely abolished by prazosin. These results suggest that 5-HT directly stimulates phospholipase C-mediated hydrolysis of phosphoinositides through 5-hydroxytryptamine-2 (5-HT2) receptors in the ventricular myocytes and that this reaction is negatively regulated by protein kinase C. 5-HT2 receptors may be coupled to phospholipase C via a pertussis toxin-insensitive GTP-binding protein in the myocytes.

Augmentation of eicosanoids in ischemic heart muscle in dogs: its role in the deterioration of the ischemic lesion

The dissolution of infarcted myocardium occurs after the infiltration of leukocytes. In the search for a mechanism of the leukocyte infiltration, we measured the production of lipoxygenase metabolites of arachidonic acid in the canine myocardium after ligation of the circumflex branch of the left coronary artery. At least 2 lipoxygenase products, namely 5- and 12-hydroxyeicosatetraenoic acids (HETEs), were augmented in myocardium subjected to ischemia lasting more than 6 hours, with levels of the latter being raised much more than the former. Augmentation of the HETEs in ischemic myocardium appeared to occur prior to any significant infiltration of leukocytes. More than 12 hours after coronary ligation, the infiltration of leukocytes became prominent and an increase in 12-HETE was observed. Calcium content in the infarcted myocardium appeared to be increased several hours before the increase in 12-HETE. These data suggest that the initial increment in 12-HETE may result from it being a product of infarcted myocardium, where Ca2+ is accumulated in the cell, and that the increased HETEs work as a leukocyte chemoattractant in infarcted myocardium. This hypothesis is supported by the independent experiment which showed that cultured cardiomyocytes produced lipoxygenase metabolites of arachidonic acid, including 12-HETEs etc, which exhibited neutrophil-chemoattractant activity when they were challenged by calcium ionophore and/or arachidonic acid. Azelastine-HCl, a lipoxygenase inhibitor, attenuated not only the above production of HETEs from the cardiomyocytes, but also production of HETEs and infiltration of neutrophils in ischemic myocardium, resulting in attenuation of the fibrous scar of infarcted myocardium.

Structural change of myofibrils during mitosis of newt embryonic myocardial cells in culture

Newt embryonic myocardial cells can undergo mitosis in culture. The successive changes in the striation pattern of sarcomeres of myofibrils during mitosis were studied by polarization microscopy without fixing or killing the cells. Birefringence of well-organized striation patterns, i.e., bright A-bands and dark I-bands, was clearly visible in interphase cells and did not show any detectable changes during incubation for 3 h or more. Electron microscopy showed the presence of well-organized myofibrils with Z-bands in these interphase cells. When myocardial cells entered the mitotic stage, the birefringence of striation pattern of their myofibrils gradually changed with the pattern in small parts of the myofibrils gradually becoming indistinct (called 'indistinct striation' in this paper). These indistinct regions increased in size during the mitotic stage. In addition, in some regions of the indistinct striation, the birefringence of sarcomeres gradually decreased and finally disappeared (called 'disappearance of sarcomeres' in this paper). No myocardial cells underwent mitosis without these disruptive changes of the myofibril striation patterns. In the post-mitotic stage, the well-organized striation of the myofibrils reappeared. Electron microscopy showed disorganized sarcomeres without Z-bands in the regions of indistinct striation, and no well-organized myofibrils in the regions where the sarcomeres had disappeared. Thus the well-organized myofibrils with Z-bands became transiently disorganized at least in some parts, during mitosis. They were then reorganized into daughter myocardial cells.

Beating activity of heterokaryons between myocardial and non-myocardial cells in culture

Cultured mouse myocardial cells grown as monolayers fused upon treatment with HVJ (Sendai virus). The myocardial cells also fused with quail myocardial cells, neuroblastoma cells and non-excitable cells, such as KB cells. The beating activity of these heterokaryons was studied in the present work. Heterokaryons composed of myocardial cells from different species maintained spontaneous beating activity for 2 days or more. Those of one myocardial and one neuroblastoma cell maintained the activity for 22-26 h, while those of one myocardial and one non-excitable cell, such as KB cell, lost the activity within 2-4 h after addition of HVJ. Heterokaryons that had stopped spontaneous beating did not contract on application of electrical-field stimulation. The ration of non-myocardial cells in the heterokaryons increased in inverse proportion to the decrease in beating activity of the heterokaryons. Study of the rapid disappearance of beating activity in heterokaryons composed of one myocardial and one KB cell showed that both excitability of the cell membrane and myofibril organization were rapidly lost.

Insulin-induced formation of ruffling membranes of KB cells and its correlation with enhancement of amino acid transport

Insulin induced the formation of ruffling membranes in cultured KB cells (a cell strain derived from human epidermoid carcinoma) within 1-2 min after its addition. The ruffled regions were stained strongly with antibody to actin but not that to tubulin. Pretreatment of KB cells with agents disrupting microfilaments (cytochalasins), but not with those disrupting microtubules (colcemid, nocodazole, and colchicine) completely inhibited the formation of ruffling membranes. Pretreatment of KB cells with dibutyryl cyclic AMP, but not with dibutyryl cyclic GMP, also inhibited the formation of ruffling membranes. Addition of insulin enhanced Na+-dependent uptake of a system A amino acid (alpha-amino isobutyric acid; AIB) by the cells within 5 min after the addition, and decreased the cyclic AMP content of the cells. Treatments that inhibited insulin-induced formation of ruffling membranes of KB cells also inhibited insulin-induced enhancement of their AIB uptake. From these observations, the mechanism of insulin-induced formation of ruffling membranes and its close correlation with AIB transport are discussed.

Inhibition of ouabain-induced increase in Na content of cultured myocardial cells by quinidine and procainamide

Addition of ouabain caused gradual increases of both the Na content of cultured myocardial cells and the rate of Ca++ uptake by the cells. Ouabain-induced irregular beating of the cells (ouabain toxicity) appeared to develop when the Na content and the rate of Ca++ uptake exceeded about 1.5 and 2.0 times, respectively, the normal levels. Quinidine and procainamide prevented ouabain-induced increases of the Na content and the rate of Ca++ uptake as well as ouabain-induced toxicity. The problem of how quinidine and procainamide counteract the effects of ouabain was then studied. Quinidine and procainamide did not affect the Na+-Ca++ exchange activity. Na+,K+-adenosine triphosphatase activity, Na+-pumping out activity or ouabain-binding activity of myocardial cells, but inhibited passive Na+ influx, which is achieved by a simple diffusion system. From these observations, it is suggested that inhibition by quinidine or procainamide of passive Na+ influx indirectly prevents ouabain-induced increase in the intracellular Na content of myocardial cells and that this presumably explains at least in part the inhibitory effect of quinidine and procainamide on ouabain-induced irregular beating.

Partial purification of Na+-Ca2+ antiporter from plasma membrane of chick heart

To study Na+-Ca2+ exchange, proteins of membrane vesicles from chick hearts were solubilized with cholate in the presence of phospholipids and the cholate extract was treated with pronase. These purified proteoliposomes, reconstituted by subsequent dilution and centrifugation to eliminate the cholate, catalyzed Ca2+ uptake depending on the intraliposomal Na+ (Nai+) concentration. The maximal amount of Ca2+ accumulating in the liposomes was 140 nmol/mg protein and the initial rates of Nai+-dependent Ca2+ uptake were routinely 20 to 40 nmol/mg per 3 s at 25 degrees C, but only 2 to 4 nmol/mg per 3 s for the crude proteoliposomes from the cholate extract not treated with pronase. Thus the pronase treatment resulted in 10-fold purification. Nai+-dependent Ca2+ uptake by purified proteoliposomes was 30- to 50-fold higher than that by the initial membrane vesicles. The fundamental properties of Nai+-dependent Ca2+ uptake in purified proteoliposomes such as Km for Ca2+, the sensitivity for Na+ and pH dependency, were nearly equal to those in membrane vesicles and crude proteoliposomes. Thus, pronase treatment was very useful for obtaining reconstituted liposomes containing highly enriched Na+-Ca2+ antiporters which were functionally intact.

Comparison of kinetic characteristics of Na+-Ca2+ exchange in sarcolemma vesicles and cultured cells from chick heart

The kinetic characteristics of Na+-Ca2+ exchange in isolated sarcolemma vesicles from new-borne chick heart, which contain about 70% of right-side-out vesicles, were compared with those of cultured embryonic chick heart cells. Na+-Ca2+ exchange was monitored as Nai-dependent Ca2+ uptake. Increase in the internal concentration of Na+ ([Na+]i) in these two preparations caused increase in both the initial rate and the saturation-level of Ca2+ uptake. Plots of the rate of Ca2+ uptake against [Na+]i showed similar saturation-kinetics in these two preparations. The apparent Michaelis constant (Km) (0.35 mM) for Ca2+ uptake by the intact cells was much higher than that (0.031 mM) for Ca2+ uptake by the vesicles. The degree of inhibition by Mg2+ was also higher in the cells than in the vesicles. Some possible reasons (age of the chicks used, membrane potential, etc.), for these differences were examined and are discussed.

Kinetic studies on sodium-dependent calcium uptake by myocardial cells and neuroblastoma cells in culture

Kinetic analyses were made on intracellular Na+-dependent Ca2+ uptake by myocardial cells and neuroblastoma cells (N-18 strain) in culture. Cells loaded with various concentrations of Na+ could be prepared by incubating them in Ca2+-free medium containing various concentrations of Na+. Cells pre-loaded with various concentrations of Na+ were incubated in medium containing Ca2+ and 45Ca. The resulting 45Ca uptake by the two types of cell depended greatly on the initial intracellular concentrations of Na+. Lineweaver-Burk plots of the initial rate of Ca2+ uptake against the external concentration of Ca2+ fitted well to straight lines obtained by linear regression (r greater than 0.95). This result shows that Ca2+ uptake by the two types of cell was achieved by a carrier-mediated transport system. This Na+-dependent Ca2+ uptake was accompanied by Na+ release and the ratio of Na+ release to Ca2+ uptake was close to 3 : 1. A comparison of the kinetic data between myocardial cells and N-18 cells suggested that N-18 cells possess a carrier showing the same properties as that of myocardial cells, i.e.: (1) a similar dependency on the intracellular concentration of Na+; (2) the coincidence of the apparent Michaelis constants for Ca2+ (0.1 mM); (3) the similarities of the Ki values for Co2+, Sr2+ and Mg2+ (Co2+ less than Sr2+ less than Mg2+) and (4) a similar dependency on pH. However, the maximal initial rate, V, of N-18 cells was about 1/100 that of myocardial cells. The rate of Na+-dependent Ca2+ uptake by non-excitable cells was much lower than that by myocardial cells.

The role of extracellular calcium ions in HVJ (Sendai virus)-induced cell fusion

The biochemical and biophysical roles of extracellular calcium ions in HVJ (Sendai virus)-induced cell fusion were studied. (1) Various kinds of cell, such as Ehrlich ascites tumor cells, mouse melanoma cells (B16-CW1 cells) and human epidermoid carcinoma cells (KB cells), could fuse in Ca2+-free medium containing a cheletor, glycoletherdiaminetetraacetic acid, in the same way as in Ca2+-containing medium. (2) The ATP content in Ehrlich ascites tumor cells decreased rapidly when the cells were treated with the virus in Ca2+-free medium but not in Ca2+-containing medium. (3) Intracellular adenine nucleotides leaked out into the reaction medium when the cells were treated with the virus in Ca2+-free medium but not in Ca2+-containing medium. (4) On addition of the virus, O2 consumption of Ehrlich ascites tumor cells decreased in Ca2+-free medium, but not in Ca2+-containing medium. (5) HVJ (Sendai virus) did not affect production of lactate by Ehrlich ascites tumor cells in both Ca2+-free medium and Ca2+-containing medium. These observations suggest that the role of extracellular Ca2+ in virus-induced cell fusion is to maintain the ATP and other intracellular metabolite contents at normal levels instead of triggering the fusion reaction itself.

Requirement of calcium ions for cell degeneration with a toxin (vibriolysin) from Vibrio parahaemolyticus

A highly purified toxin (vibriolysin) from Vibrio parahaemolyticus caused degeneration of cell shape, such as bleb and balloon formation, of mouse myocardial cells and mouse melanoma cells in culture. An extracellular Ca2+ concentration of more than 10(-6) M was necessary for the degeneration of cell shape, but extracellular Mg2+, Na+, and K+ were not necessary. In the presence of extracellular Ca2+, vibriolysin also caused full contraction of myofibrils of mouse myocardial cells and reduction of both actin cables and tubulin networks of mouse melanoma cells. Vibriolysin also caused excess uptake of Ca2+ from the incubation medium by mouse myocardial cells and mouse melanoma cells. Chick myocardial cells, which show neither degeneration of cell shape nor full contraction of myofibrils, did not take up excess 45Ca2+ in the presence of vibriolysin. These findings suggest that the vibriolysin-induced degeneration of cell shape of mouse myocardial cells and mouse melanoma cells is due to excess uptake of Ca2+ from the incubation medium by the cells.