Kimiaki Komukai

Gender and the renin–angiotensin–aldosterone system

Premenopausal women are protected to some extent from cardiovascular and kidney diseases. Because this protection weakens after menopause, sex hormones are believed to play an important role in the pathogenesis of cardiovascular and kidney diseases. The cardiovascular system and the kidneys are regulated by the renin–angiotensin–aldosterone system (RAAS), which in turn, appears to be regulated by sex hormones. In general, oestrogen increases angiotensinogen levels and decreases renin levels, angiotensin‐converting enzyme (ACE) activity, AT1 receptor density, and aldosterone production. Oestrogen also activates counterparts of the RAAS such as natriuretic peptides, AT2 receptor density, and angiotensinogen (1‐7). Progesterone competes with aldosterone for mineralocorticoid receptor. Less is known about androgens, but testosterone seems to increase renin levels and ACE activity. These effects of sex hormones on the RAAS can explain at least some of the gender differences in cardiovascular and kidney diseases.

Interaction of α1-Adrenoceptor Subtypes With Different G Proteins Induces Opposite Effects on Cardiac L-type Ca2+ Channel

We examined the effect of &agr;1-adrenoceptor subtype-specific stimulation on L-type Ca2+ current (ICa) and elucidated the subtype-specific intracellular mechanisms for the regulation of L-type Ca2+ channels in isolated rat ventricular myocytes. We confirmed the protein expression of &agr;1A- and &agr;1B-adrenoceptor subtypes at the transverse tubules (T-tubules) and found that simultaneous stimulation of these 2 receptor subtypes by nonsubtype selective agonist, phenylephrine, showed 2 opposite effects on ICa (transient decrease followed by sustained increase). However, selective &agr;1A-adrenoceptor stimulation (≥0.1 &mgr;mol/L A61603) only potentiated ICa, and selective &agr;1B-adrenoceptor stimulation (10 &mgr;mol/L phenylephrine with 2 &mgr; mol/L WB4101) only decreased ICa. The positive effect by &agr;1A-adrenoceptor stimulation was blocked by the inhibition of phospholipase C (PLC), protein kinase C (PKC), or Ca2+/calmodulin-dependent protein kinase II (CaMKII). The negative effect by &agr;1B-adrenoceptor stimulation disappeared after the treatment of pertussis toxin or by the prepulse depolarization, but was not attriburable to the inhibition of cAMP-dependent pathway. The translocation of PKC&dgr; and ϵ to the T-tubules was observed only after &agr;1A-adrenoceptor stimulation, but not after &agr;1B-adrenoceptor stimulation. Immunoprecipitaion analysis revealed that &agr;1A-adrenoceptor was associated with Gq/11, but &agr;1B-adrenoceptor interacted with one of the pertussis toxin-sensitive G proteins, Go. These findings demonstrated that the interactions of &agr;1-adrenoceptor subtypes with different G proteins elicit the formation of separate signaling cascades, which produce the opposite effects on ICa. The coupling of &agr;1A-adrenoceptor with Gq/11-PLC-PKC-CaMKII pathway potentiates ICa. In contrast, &agr;1B-adrenoceptor interacts with Go, of which the &bgr;&ggr;-complex might directly inhibit the channel activity at T-tubules.

Role of Ca2+/calmodulin-dependent protein kinase II in the regulation of the cardiac L-type Ca2+ current during endothelin-1 stimulation

Endothelin-1 (ET-1) shows a positive inotropic effect on cardiac muscle. Although the L-type Ca(2+) current (I(Ca)) is one of the important determinants of cardiac excitation-contraction coupling, the effect of ET-1 on the I(Ca) is not always clear. The controversial results appear to be due to different patch-clamp methods. The present study measured the effect of ET-1 on the I(Ca) of rat ventricular myocytes using the perforated patch-clamp technique. The holding potential was set to -40 mV, and depolarization was applied every 10 s. ET-1 (10 nM) increased the I(Ca) in a monophasic manner. The current reached a steady state 15 min after the application of ET-1, when the measurement was done. Endothelin receptor subtype expression was also investigated using Western immunoblotting. ET(A)-receptor protein was expressed, but ET(B)-receptor protein was not expressed, in the cell membranes of rat ventricular myocytes. The effect of ET-1 on the I(Ca) was inhibited by a selective ET(A)-receptor antagonist, BQ-123, but not by a selective ET(B)-receptor antagonist, BQ-788. The effect was inhibited by protein kinase C (PKC) inhibitor chelerythrine and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) inhibitor KN-93, but not by its inactive analog KN-92. The effect of ET-1 was also blocked by another CaMKII inhibitor, autocamtide-2-related inhibitory peptide. These results suggest that ET-1 increases the I(Ca) via the ET(A)-receptor-PKC-CaMKII pathway.

Effects of acidosis on Ca2+sensitivity of contractile elements in intact ferret myocardium

We investigated the effects of acidosis on the intracellular Ca2+ concentration ([Ca2+]i) and contractile properties of intact mammalian cardiac muscle during tetanic and twitch contractions. Aequorin was injected into ferret papillary muscles, and the [Ca2+]iand tension were simultaneously measured. Acidosis was attained by increasing the CO2 concentration in the bicarbonate (20 mM)-buffered Tyrode solution from 5% (pH 7.35, control) to 15% (pH 6.89, acidosis). Tetanic contraction was produced by repetitive stimulation of the preparation following treatment with 5 μM ryanodine. The relationship between [Ca2+]iand tension was measured 6 s after the onset of the stimulation and was fitted using the Hill equation. Acidosis decreased the maximal tension to 81 ± 2% of the control and shifted the [Ca2+]i-tension relationship to the right by 0.18 ± 0.01 pCa units. During twitch contraction, a quick shortening of muscle length from the length at which developed tension became maximal ( L max) to 92% L maxproduced a transient change in the [Ca2+]i(extra Ca2+). The magnitude of the extra Ca2+ was dependent on the [Ca2+]iimmediately before the length change, suggesting that the extra Ca2+ is related to the amount of troponin-Ca complex. Acidosis decreased the normalized extra Ca2+ to [Ca2+]iimmediately before the length change, which indicates that the amount of Ca2+ bound to troponin C is less when [Ca2+]iis the same as in the control. The decrease in the Ca2+ binding to troponin C explains the decrease in tetanic and twitch contraction, and mechanical stress applied to the preparation induced less [Ca2+]ichange in acidosis.

Protein kinase A-dependent phosphorylation of ryanodine receptors increases Ca2+ leak in mouse heart.

In heart failure, chronic catecholaminergic stimulation increases diastolic Ca(2+) leak from ryanodine receptors (RyRs) of sarcoplasmic reticulum (SR), possibly due to the phosphorylation of RyRs through the activation of protein kinase A (PKA) or Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). In the present study, we attempted to identify which activated kinase is responsible for the enhanced Ca(2+) leak caused by beta-adrenergic stimulation. Trabeculae obtained from the hearts of adult male C57BL/6J mice were treated with isoproterenol and then permeabilized with saponin. To examine SR functions, Ca(2+) in SR was released with caffeine and measured with fluo-3. The Ca(2+) leak in isoproterenol-treated preparations was significantly increased when the PKA-dependent phosphorylation of RyR was increased without the involvement of CaMKII-dependent phosphorylation. Both the increase in Ca(2+) leak and the phosphorylation of RyR were blocked by a PKA inhibitor. Our results show that beta-adrenergic stimulation increases Ca(2+) leak from SR through PKA-dependent phosphorylation of RyR.

Difference in risk factors between acute coronary syndrome and stable angina pectoris in the Japanese: smoking as a crucial risk factor of acute coronary syndrome.

BACKGROUND AND PURPOSE Metabolic syndrome and chronic kidney disease (CKD) have received attention as new risk factors for cardiovascular disease. This study evaluated differences in key risk factors between acute coronary syndrome (ACS) and stable angina pectoris (SAP) by using traditional coronary risk factors, metabolic syndrome, and CKD. METHODS Among 1890 consecutive patients admitted to our institution, we studied 140 patients with initially diagnosed ACS and 163 patients with initially diagnosed SAP and compared risk factors between the two groups. Next, the relationship between smoking status after the initial diagnosis of coronary artery disease (CAD) and the incidence of subsequent cardiac event was examined after discharge in 284 patients. RESULTS Adjusted multivariate analysis showed that only current smoking was an independent predictor of ACS (odds ratio, 2.20; 95% CI, 1.28-3.78; p=0.004) among all risk factors we examined. Treatment with a calcium-channel blocker had a preventive effect on ACS (odds ratio, 0.44; 95% CI, 0.26-0.75; p=0.003), but treatment with a beta-blocker did not. Patients who continued to smoke after CAD was diagnosed had a risk of cardiac events about 5 times that of smokers who quit (adjusted hazard ratio, 5.05; 95% CI, 1.33-19.20; p=0.02). CONCLUSIONS The risk factors were significantly different between initially diagnosed ACS and SAP. Smoking was a more important risk factor of initially diagnosed ACS. Smoking cessation might have a preventive effect on subsequent cardiac events. Also, we found that treatment with a calcium-channel blocker would help prevent ACS in Japanese patients.

Scoring of late gadolinium enhancement in cardiac magnetic resonance imaging can predict cardiac events in patients with hypertrophic cardiomyopathy

BACKGROUND Late gadolinium enhancement (LGE) of cardiac magnetic resonance imaging (MRI) represents myocardial fibrosis and may be related to the clinical outcome of various heart diseases. This study evaluated the relationship between LGE and cardiac events in hypertrophic cardiomyopathy (HCM) using a new scoring method. METHODS AND RESULTS This study retrospectively followed 46 HCM patients without heart failure symptoms for 3.8 ± 1.8 years. Gadolinium-enhanced cardiac MRI was performed in all patients. Cardiac events including newly developed heart failure or ventricular tachyarrhythmia were evaluated during the follow-up period. We evaluated the predictive factors to identify the patients with cardiac events. None of the risk factors reported to be related to poor outcome or the existence of LGE alone could predict cardiac events, which might be due to the small number of subjects investigated in this study. A new scoring method for LGE-positive areas (LGE score) was applied and higher LGE score can predict cardiac events in this study population. CONCLUSIONS The proposed LGE score for cardiac MRI is considered to be a potentially valid method for assessing cardiac events in HCM patients.

Effect of developed tension on the time courses of Ca2+ transients and tension in twitch contraction in ferret myocardium

OBJECTIVES The aim of the study is to test the hypothesis that tension-dependent change in the affinity of cardiac troponin-C influences the time courses of Ca2+ transients and tension in twitch contraction. METHODS The Ca(2+)-sensitive photoprotein, aequorin, was microinjected into superficial cells of ferret papillary muscles and the Ca2+ transients and tension were simultaneously measured. The peak of developed tension was altered by changing the extracellular Ca2+ concentration, initial muscle length, and the application of 2,3-butanedione monoxime. RESULTS In each maneuver, the decay time of Ca2+ transients was prolonged and the tension relaxation time was shortened when the peak of developed tension was decreased. In contrast, when the peak of developed tension was increased, the decay time of Ca2+ transients was shortened and the tension relaxation time was prolonged. The decay time of Ca2+ transients measured with different maneuvers was negatively correlated with the peak tension and the tension relaxation time was positively correlated with the tension peak. CONCLUSIONS The changes in the decay time of Ca2+ transients and the tension relaxation time indicate that developed tension modulates the affinity of troponin-C for Ca2+ in normal twitch contraction.

Elevated Plasma Brain Natriuretic Peptide Level in Cardiac Sarcoidosis Patients with Preserved Ejection Fraction

We sought to examine whether the plasma brain natriuretic peptide (BNP) levels are elevated in the cardiac sarcoidosis patients even with a preserved ejection fraction. The data from the patients with either pulmonary sarcoidosis without any evidence of cardiac involvement (n = 13) or cardiac sarcoidosis (n = 8) with a preserved ejection fraction (>55%) on echocardiography were analyzed. The median plasma BNP levels were significantly higher in the patients with cardiac sarcoidosis than in those with pulmonary sarcoidosis (101.5 ± 65.1 vs. 15.6 ± 10.5 pg/ml, p < 0.001), although there was no significant difference in left ventricular ejection fraction between the two populations. The plasma BNP level is thus considered to be a useful non-invasive biomarker for identifying a possible cardiac involvement in the sarcoidosis patients with a preserved ejection fraction.

Transient decrease in serum potassium level during ischemic attack of acute coronary syndrome: Paradoxical contribution of plasma glucose level and glycohemoglobin

BackgroundAlthough a decrease in serum potassium level has been suggested to be a fairly common observation in acute coronary syndrome (ACS), there have so far been no definitive reports directly demonstrating the transient potassium decrease (the potassium dip) during ischemic attack of ACS compared to stable phase in individual patients. To understand the pathophysiological significance of the potassium dip, we examined the changes in serum potassium level throughout ischemic attack and evaluated the clinical factors affecting it.MethodsThe degree of the potassium dip during ischemic attack (as indicated by ΔK, ΔK = K at discharge − K on admission) was examined in 311 consecutive patients with ACS who required urgent hospitalization in our institution.ResultsSerum potassium level during ischemic attack was significantly decreased compared to that during stable phase (P < 0.001). Multiple regression analysis revealed that plasma glucose level during attack was the sole factor which was positively correlated with ΔK (P < 0.01), while HbA1c level was negatively correlated (P < 0.05). The medication profiles and renal function had no impact on ΔK. A longer hospitalization period, higher incidence of myocardial infarction and higher peak creatine kinase level were observed in patients with a larger ΔK.ConclusionsWe have clearly demonstrated that there is a transient decrease in serum potassium level during ischemic attack of ACS compared to stable phase. The degree of the potassium dip was tightly correlated with glucose level, which overwhelmed the diabetic condition, and it also indicates the disease severity. The present study therefore promotes awareness of the significance of monitoring potassium level in parallel with glucose level in patients with ACS.