Morphine mimics preconditioning via free radical signals and mitochondrial K(ATP) channels in myocytes.
BACKGROUND: We tried to determine whether morphine mimics preconditioning (PC) to reduce cell death in cultured cardiomyocytes and whether opioid delta(1) receptors, free radicals, and K(ATP) channels mediate this effect. METHODS AND RESULTS: Chick embryonic ventricular myocytes were studied in a flow-through chamber while flow rate, pH, and O(2) and CO(2) tension were controlled. Cardiomyocyte viability was quantified with propidium iodide (5 micromol/L), and production of free radicals was measured with 2',7'-dichlorofluorescin diacetate. PC with 10 minutes of simulated ischemia before 10 minutes of reoxygenation or morphine (1 micromol/L) or BW373U86 (10 pmol/L) infusion for 10 minutes followed by a 10-minute drug-free period before 1 hour of ischemia and 3 hours of reoxygenation reduced cell death to the same extent (*P:<0.05) (PC, 20+/-1%, n=7*; morphine, 32+/-4%, n=8*; BW373U86, 21+/-6%; controls, 52+/-5%, n=8). Like PC, morphine and BW373U86 increased free radical production 2-fold before ischemia (0.35+/-0.10, n=6*; 0.41+/-0.08, n=4* versus controls, 0.15+/-0.05, n=8, arbitrary units). Protection and increased free radical signals during morphine infusion were abolished with either the thiol reductant 2-mercaptopropionyl glycine (400 micromol/L), an antioxidant; naloxone (10 micromol/L), a nonselective morphine receptor antagonist; BNTX (0.1 micromol/L), a selective opioid delta(1) receptor antagonist; or 5-hydroxydecanoate (100 micromol/L), a selective mitochondrial K(ATP) channel antagonist. CONCLUSIONS: These results suggest that direct stimulation of cardiocyte opioid delta(1) receptors leads to activation of mitochondrial K(ATP) channels. The resultant increase of intracellular free radical signals may be an important component of the signaling pathways by which morphine mimics preconditioning in cardiomyocytes. (+info)
Treatment with a growth hormone secretagogue in a model of developing heart failure: effects on ventricular and myocyte function.
BACKGROUND: Exogenous administration of growth hormone (GH) and subsequently increased production of insulin-like growth factor-1 can influence left ventricular (LV) myocardial growth and geometry in the setting of congestive heart failure (CHF). This study determined the effects of an orally active GH secretagogue (GHS) treatment that causes a release of endogenous GH on LV function and myocyte contractility in a model of developing CHF. METHODS AND RESULTS: Pigs were randomly assigned to the following treatment groups: (1) chronic rapid pacing at 240 bpm for 3 weeks (n=11); (2) chronic rapid pacing and GHS (CP-424,391 at 10 mg x kg(-1) x d(-1), n=9); and (3) sham controls (n=8). In the untreated pacing CHF group, LV fractional shortening was reduced (21+/-2% versus 47+/-2%) and peak wall stress increased (364+/-21 versus 141+/-5 g/cm(2)) from normal control values (P:<0.05). In the GHS group, LV fractional shortening was higher (29+/-2%) and LV peak wall stress lower (187+/-126 g/cm(2)) than untreated CHF values (P:<0.05). With GHS treatment, the ratio of LV mass to body weight increased by 44% from untreated values. Steady-state myocyte velocity of shortening was reduced with pacing CHF compared with controls (38+/-1 versus 78+/-1 microm/s, P:<0.05) and was increased from pacing CHF values with GHS treatment (55+/-7 microm/s, P:<0.05). CONCLUSIONS: The improved LV pump function that occurred with GHS treatment in this model of CHF was most likely a result of favorable effects on LV myocardial remodeling and contractile processes. On the basis of these results, further studies are warranted to determine the potential role of GH secretagogues in the treatment of CHF. (+info)
Eicosanoids participate in the regulation of cardiac glucose transport by contribution to a rearrangement of actin cytoskeletal elements.
Intact actin microfilaments are required for insulin-regulated glucose transporter isoform 4 (GLUT4) translocation to the plasma membrane. Lipoxygenase (LO) metabolites have recently been shown to contribute to the regulation of actin cytoskeleton rearrangement. In the present investigation, ventricular cardiomyocytes were used to study the effects of two structurally different LO inhibitors (esculetin and nordihydroguaiaretic acid) on insulin signalling events, glucose uptake, GLUT4 translocation and the actin network organization. Insulin stimulation increased glucose uptake 3-fold in control cells, whereas LO inhibition completely blocked this effect. This was paralleled by a slight reduction in the insulin-induced tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and IRS-2. However, inhibition of 12-LO did not affect the association of phosphatidylinositol 3-kinase with IRS-1 and the phosphorylation of Akt/protein kinase B in response to insulin. Addition of 12(S)-hydroxyeicosatetraenoic acid almost completely restored the insulin action in cells exposed to nordihydroguaiaretic acid. Insulin stimulation increased cell surface GLUT4 2-fold in control cells, whereas LO inhibition abrogated the insulin-stimulated GLUT4 translocation. LO inhibition induced a prominent disassembly of actin fibres compared with control cells. In conclusion, we show here that 12(S)-hydroxyeicosatetraenoic acid plays a role in the organization of the actin network in cardiomyocytes. LO inhibition blocks GLUT4 translocation without affecting downstream insulin signalling. These data suggest that LO metabolites participate in the regulation of glucose transport by contributing to a rearrangement of actin cytoskeletal elements. (+info)
Stimulation by melittin of Na+-Ca2+ exchange current in ventricular myocytes of guinea pigs.
AIM: To study the mechanism of calcium overload induced by melittin in myocytes. METHODS: Whole cell patch-clamp technique was applied for recording the currents. RESULTS: Mel 0.05, 0.1 micromol/L increased the peak amplitude of I(Na) (nA) from -2.1+/-0.8 to -3.2+/-1.0 (n=7, P < 0.05) and -3.7+/-1.5 (n=7, P < 0.05) respectively at testing potential of -40 mV. Mel 0.05, 0.1, 0.2 micromol/L had no significant effect on I(Ca), but enhanced I(Na-Ca) (pA) from 53+/-21 to 427+/-256 (n=5, P < 0.05), 349+/-147 (n=5, P<0.01) and 320+/-97 (n=5, P < 0.05) respectively at a testing potential of +50 mV. CONCLUSION: The stimulating effect of Mel on I(Na-Ca) rather than the effect on I(Ca) contributes to the calcium overload of myocytes. (+info)
Inhibitory effects of berberine on IK1, IK, and HERG channels of cardiac myocytes.
AIM: To study the effects of berberine on inward rectifier potassium current (IK1) and outward delayed rectifier potassium current (IK) of guinea pig ventricular myocytes, and on human ether-a-go-go related gene (HERG) channel expressed in Xenopus oocytes. METHODS: Whole cell patch-clamp and geneclamp techniques were used to record ionic currents. RESULTS: Berberine prolonged action potential duration (APD) and inhibited IK1 and IK in a concentration-dependent manner. Berberine 100 micromol/L increased APD90 from (450 +\- 48) ms to (888 +\- 90) ms (n = 6, P < 0.01), and inhibited IK1 by 65 % +\- 7 % (n = 6, P < 0.01). Berberine 50 micromol/L inhibited IK by 57 % +\- 6 %, IKtail by 53 % +\- 6 % (n = 6, P < 0.01). Berberine produced a voltage-dependent block on IK that increased with stronger depolarization, and once all channels were activated, there was no further block at positive potentials. Berberine blocked the HERG channels potently with an IC50 value of approximately 75 micromol/L. This block was voltage-dependent, suggesting that it probably bind to either open or inactivated HERG channels. CONCLUSION: Berberine prolonged APD and possessed blocking effect on IK1, IK, and HERG channel expressed in Xenopus oocytes. The antiarrhythmic mechanism of berberine is related to its inhibitory effects on IK1, IK, and HERG channel. (+info)
Effects of matrine, artemisinin, tetrandrine on cytosolic [Ca2+]i in guinea pig ventricular myocytes.
AIM: To compare the effects of matrine, artemisinin, and tetrandrine on intracellular Ca2+ concentration ([Ca2+]i) in guinea pig ventricular myocytes. METHODS: A single ventricular myocyte was loaded with Fluo 3-acetoxymethyl (Fluo 3-AM). [Ca2+]i was recorded by laser scanning confocal microscope and represented by fluorescence intensity (FI). RESULTS: 1) KCl 60 mmol . L-1 elevated the FI from 299 +/ -19 to 1389 +/- 325 (P < 0.01) in the presence of extracellular Ca2+ 1.8 mmol . L-1. 2) Both matrine and artemisinin at the concentration of 100 micromol . L-1 could enhance the increase of FI by KCl 60 mmol . L-1. The FI values reached 1495 +/- 320 and 1646 +/- 308 from 301 +/- 14 and 299 +/- 16 (P < 0.01), respectively. 3) Both tetrandrine 1, 10, and 100 micromol . L-1 and verapamil 10 micromol . L-1 inhibited the influx of extracellular Ca2+ induced by KCl 60 mmol . L-1. 4) Matrine 1, 10, and 100 micromol . L-1 could elevate the FI in the presence of extracellular Ca2+. The FI values reached 441 +/- 96, 504 +/- 112, and 643 +/- 126 from 303 +/- 27, 300 +/- 32, and 296 +/- 19 (P < 0.05), respectively. 5) Tetrandrine 1 and 10 micromol . L-1 could apparently inhibited Ca2+ release from intracellular calcium stores induced by caffeine 20 mmol . L-1 (P < 0.05). CONCLUSION: Effects of matrine, artemisinin, and tetrandrine on [Ca2+ )]i in ventricular (+info)
Inhibitory effect of quercetin on cultured neonatal rat cardiomyocytes hypertrophy induced by angiotensin.
AIM: To study the inhibitory effect of quercetin on cultured neonatal rat cardiomyocytes hypertrophy induced by angiotensin II (AngII) and its mechanism. METHODS: DNA, RNA, and protein synthesis were measured by incorporation of [3H]thymidine, [14C]uridine, and [3H]tyrosine, respectively. Protein content were measured by Lowry's method. Protein kinase C (PKC) activity was assayed by incubating PKC with histone IIIS and [gamma-(32)P]ATP. Tyrosine protein kinase (TPK) activity was assayed by incubating TPK with poly glutamate/tyrosine (4:1) and [gamma-(32P]ATP. RESULTS: After treated with AngIIat 10 nmol/L for 24 h, total protein content was greatly increased as compared with untreated group (P < 0.01). Incorporation of [14C]uridine and [3H]tyrosine was also greatly increased (P < 0.01) respectively, while incorporation of [3H]thymidine remained unchanged (P > 0.05). Ang II strongly increased cardiomyocytes PKC and TPK activities at 30 min. Que (1-100 micromol/L) could inhibit the increase of total protein content, incorporation of [14C]uridine and [3H]tyrosine, and PKC and TPK activities induced by Ang II in concentration-dependent manner. CONCLUSION: The inhibitory effect of Que on the cardiomyocytes hypertrophy was related to its inhibitory effect on PKC and TPK. (+info)
Effect of sea anemone toxin anthopleurin-Q on sodium current in guinea pig ventricular myocytes.
AIM: To investigate the effects of a sea anemone toxin anthopleurin-Q (AP-Q) isolated from Anthopleura xanthogrammica on sodium current (INa) in isolated guinea pig ventricular myocytes. METHODS: Single myocytes were dissociated by enzymatic dissociation method. INa was recorded using whole-cell patch-clamp technique. RESULTS: AP-Q (3 - 300 nmol/L) increased INa in a concentration-dependent manner. The EC50 value for increasing INa was 104 nmol/L (95 % confidence range: 78 - 130 nmol/L). AP-Q 300 nmol/L shifted the I-V curve to the leftward, changed the membrane potential of half maximal activation to more negative potential from (-36.3 +/- 2.3) mV to (-43 +/- 3) mV (n = 6, P < 0.01) and changed the membrane potential of half maximal inactivation to more positive potential from (-75 +/- 6) mV to (-59 +/- 5) mV (n = 6, P < 0.01). AP-Q 300 nmol/L shortened the half-recovery time of INa from (114 +/- 36) ms to (17 +/- 2) ms (n = 6, P < 0.01). The fast inactivation time constant (tauf) of INa was markedly increased by AP-Q 300 nmol/L. CONCLUSION: AP-Q has a stimulating effect on I(Na) with slowing the inactivation course of INa. (+info)