Intracellular pH regulation in isolated myocytes from adult rat heart in HCO-3-containing and HCO-3-free media

1993 ◽  
Vol 84 (2) ◽  
pp. 133-139 ◽  
Author(s):  
L. L. Ng ◽  
J. E. Davies ◽  
P. Quinn
Keyword(s):  
Intracellular Ph ◽  
Ventricular Myocytes ◽  
Ph Regulation ◽  
Specific Inhibitor ◽  
Buffering Capacity ◽  
Intracellular Acidosis ◽  
Rat Ventricular Myocytes ◽  
Adult Rat ◽  
Acid Load ◽  
Free Media

1. Using microfluorimetry, intracellular pH, buffering capacity and intracellular pH recovery from intracellular acidosis were determined in isolated adult rat ventricular myocytes, in buffers with and without HCO-3. 2. In nominally HCO-3-free media, the intracellular pH was higher than in HCO-3-containing media. Buffering capacity at resting intracellular pH and at a pH of about 6.3 was also lower in HCO-3-free media. 3. In HCO-3-free media, recovery from an acid load after an NH4C1 prepulse was almost completely inhibited by the Na+/H+ antiport activity specific inhibitor ethylisopropyl amiloride. However, in the presence of HCO-3, H+ efflux rate was enhanced, and ethylisopropyl amiloride led to only partial inhibition of H+ efflux. Complete inhibition was achieved only with further addition of the anion-transport inhibitor 4,4′-di-isothiocyanatostilbene-2,2′-disulphonate. 4. Thus, in adult rat ventricular myocytes, recovery from intracellular acidosis in the absence of HCO-3 was almost wholly due to Na+/H+ antiport activity. In the more physiological situation with HCO-3 present, a third of the recovery from an intracellular acid load was attributed to an additional external Na+-dependent di-isothiocyanatostilbene-disulphonate-sensitive H+ efflux.

Propofol Increases Myofilament Ca2+Sensitivity and Intracellular pH via  Activation of Na+–H+Exchange in Rat Ventricular Myocytes

2001 ◽  
Vol 94 (6) ◽  
pp. 1096-1104 ◽  
Author(s):  
Noriaki Kanaya ◽  
Paul A. Murray ◽  
Derek S. Damron
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Intracellular Ph ◽  
Ventricular Myocytes ◽  
Intracellular Acidosis ◽  
Solution Ph ◽  
Rat Ventricular Myocytes ◽  
Actomyosin Atpase ◽  
Adult Rat ◽  
Kinase C

Background The objectives were to determine the extent and mechanism of action by which propofol increases myofilament Ca2+ sensitivity and intracellular pH (pHi) in ventricular myocytes. Methods Freshly isolated adult rat ventricular myocytes were used for the study. Cardiac myofibrils were extracted for assessment of myofibrillar actomyosin adenosine triphosphatase (ATPase) activity. Myocyte shortening (video edge detection) and pHi (2',7'-bis-(2-carboxyethyl)-5(6')-carboxyfluorescein, 500/440 ratio) were monitored simultaneously in individual cells field-stimulated (0.3 Hz) and superfused with HEPES-buffered solution (pH 7.4, 30 degrees C). Results Propofol (100 microM) reduced the Ca2+ concentration required for activation of myofibrillar actomyosin ATPase from pCa 5.7 +/- 0.01 to 6.6 +/- 0.01. Increasing pHi (7.05 +/- 0.03 to 7.39 +/- 0.04) with NH4Cl increased myocyte shortening by 35 +/- 12%. Washout of NH4Cl decreased pHi to 6.82 +/- 0.03 and decreased myocyte shortening to 52 +/- 10% of control. Propofol caused a dose-dependent increase in pHi but reduced myocyte shortening. The propofol-induced increase in pHi was attenuated, whereas the decrease in myocyte shortening was enhanced after pretreatment with ethylisopropyl amiloride, a Na+-H+ exchange inhibitor, or bisindolylmaleimide I, a protein kinase C inhibitor. Propofol also attenuated the NH4Cl-induced intracellular acidosis, increased the rate of recovery from acidosis, and attenuated the associated decrease in myocyte shortening. Propofol caused a leftward shift in the extracellular Ca2+-shortening relation, and this effect was attenuated by ethylisopropyl amiloride. Conclusions These results suggest that propofol increases the sensitivity of myofibrillar actomyosin ATPase to Ca2+ (ie., increases myofilament Ca2+ sensitivity), at least in part by increasing pHi via protein kinase C-dependent activation of Na+-H+ exchange.

Beta 2-adrenergic receptors enhance contractility by stimulating HCO3(-)-dependent intracellular alkalinization

1997 ◽  
Vol 273 (2) ◽  
pp. H1044-H1047 ◽  
Author(s):  
T. Jiang ◽  
S. F. Steinberg
Keyword(s):  
Intracellular Ph ◽  
Adrenergic Receptors ◽  
Ventricular Myocytes ◽  
Electrical Field Stimulation ◽  
Inotropic Response ◽  
Signaling Mechanism ◽  
Rat Ventricular Myocytes ◽  
Adult Rat ◽  
Beta 2 ◽  
Intracellular Alkalinization

Previous studies established that beta 2-adrenergic receptors enhance the amplitude, without abbreviating the kinetics, of the twitch in adult rat ventricular myocytes. The present study was designed to identify the dominant signaling mechanism mediating this response. Myocytes from adult rat ventricles were loaded with the pH-sensitive fluorophore 2',7'-bis(carboxyethyl)-5(6')-carboxyfluorescein, and simultaneous measurements of intracellular pH and contraction were performed during electrical field stimulation under basal conditions and after stimulation with isoproterenol or the selective beta 2-receptor agonist zinterol. Inhibition of protein kinase A with H-7 completely inhibited the isoproterenol-dependent, but not the zinterol-dependent, positive inotropic response. The effect of zinterol to increase twitch amplitude was associated with an alkalinization of 0.07 +/- 0.02 pH unit, which was not prevented by inhibition of the Na+/H+ exchanger with hexamethylene-amiloride. Rather, removal of bicarbonate from the extracellular buffer prevented the beta 2-receptor-dependent alkalinization as well as the positive inotropic response. These results indicate that beta 2-adrenergic receptors induce a positive inotropic response in adult rat ventricular myocytes via a adenosine 3',5'-cyclic monophosphate-independent mechanism that involves intracellular alkalinization due to activation of a bicarbonate-dependent intracellular pH regulatory mechanism.

p38 MAP kinase inhibitor reverses stress-induced cardiac myocyte dysfunction

2005 ◽  
Vol 98 (1) ◽  
pp. 77-82 ◽  
Author(s):  
Hong Kan ◽  
Dale Birkle ◽  
Abnash C. Jain ◽  
Conard Failinger ◽  
Sherry Xie ◽  
...  
Keyword(s):  
Map Kinase ◽  
Cardiac Myocyte ◽  
Kinase Inhibitor ◽  
Ventricular Myocytes ◽  
Myocardial Dysfunction ◽  
P38 Map Kinase ◽  
Border Detection ◽  
Rat Ventricular Myocytes ◽  
Adult Rat ◽  
Fractional Shortening

Stress is gaining increasing acceptance as an independent risk factor contributing to adverse cardiovascular outcomes. Potential mechanisms responsible for the deleterious effects of stress on the development and progression of cardiovascular disease remain to be elucidated. An established animal model of stress in humans is the prenatally stressed (PS) rat. We stressed rats in their third trimester of pregnancy by daily injections of saline and moving from cage to cage. Male offspring of these stressed dams (PS) and age-matched male control offspring (control) were further subjected to restraint stress (R) at 6 and 7 wk of age. Echocardiography revealed a significant decrease in fractional shortening in PS + R vs. controls + R (45.8 ± 3.9 vs. 61.9 ± 2.4%, PS + R vs. controls + R; P < 0.01; n = 12). Isolated adult rat ventricular myocytes from PS + R also revealed diminished fractional shortening (6.7 ± 0.8 vs. 12.7 ± 1.1%, PS + R vs. controls + R; P < 0.01; n = 24) and blunted inotropic responses to isoproterenol ( P < 0.01; n = 24) determined by automated border detection. The p38 mitogen-activated protein (MAP) kinase inhibitor SB-203580 blocked p38 MAP kinase phosphorylation, reversed the depression in fractional shortening, and partially ameliorated the blunted adrenergic signaling seen in adult rat ventricular myocytes from PS + R. Phosphorylation of p38 MAP kinase in cardiac myocytes by stress may be sufficient to lead to myocardial dysfunction in animal models and possibly humans.

Protein kinase Cε and the antiadrenergic action of adenosine in rat ventricular myocytes

2004 ◽  
Vol 287 (4) ◽  
pp. H1721-H1729 ◽  
Author(s):  
Koji Miyazaki ◽  
Satoshi Komatsu ◽  
Mitsuo Ikebe ◽  
Richard A. Fenton ◽  
James G. Dobson
Keyword(s):  
Electrical Stimulation ◽  
Protein Kinase ◽  
Ventricular Myocytes ◽  
Adrenergic Agonist ◽  
Inhibitory Peptide ◽  
Rat Ventricular Myocytes ◽  
Adult Rat ◽  
Tubular System ◽  
Stimulation Of

Adenosine-induced antiadrenergic effects in the heart are mediated by adenosine A1 receptors (A1R). The role of PKCε in the antiadrenergic action of adenosine was explored with adult rat ventricular myocytes in which PKCε was overexpressed. Myocytes were transfected with a pEGFP-N1 vector in the presence or absence of a PKCε construct and compared with normal myocytes. The extent of myocyte shortening elicited by electrical stimulation of quiescent normal and transfected myocytes was recorded with video imaging. PKCε was found localized primarily in transverse tubules. The A1R agonist chlorocyclopentyladenosine (CCPA) at 1 μM rendered an enhanced localization of PKCε in the t-tubular system. The β-adrenergic agonist isoproterenol (Iso; 0.4 μM) elicited a 29–36% increase in myocyte shortening in all three groups. Although CCPA significantly reduced the Iso-produced increase in shortening in all three groups, the reduction caused by CCPA was greatest with PKCε overexpression. The CCPA reduction of the Iso-elicited shortening was eliminated in the presence of a PKCε inhibitory peptide. These results suggest that the translocation of PKCε to the t-tubular system plays an important role in A1R-mediated antiadrenergic actions in the heart.

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