Are Prostanoids Related to Positive Inotropism by UTP and ATP?

We investigated the contribution of maximal Ca(2+)-activated force to the positive inotropism induced by mild hypothermia. Phosphorus-31 nuclear magnetic resonance spectroscopy revealed that neither energy-related phosphorus compounds in myocardium nor intracellular pH was responsible for the change in contractility. Maximal Ca(2+)-activated pressure (MCAP), the intact-heart correlate of maximal Ca(2+)-activated force, was determined in isolated perfused rabbit hearts by measuring isovolumic left ventricular pressure during tetani at extracellular Ca2+ concentrations greater than or equal to 10 mM. Tetani were elicited by rapid pacing after exposure to ryanodine. MCAP increased by 2.17 +/- 0.28% (mean +/- SE, P less than 0.001, n = 19) for each degree of myocardial cooling between 30 and 38 degrees C. Our results indicate that a primary change in myofilament Ca2+ responsiveness underlies the positive inotropism in hypothermia. The increase in maximal Ca(2+)-activated force may explain the observation of positive inotropism without an upward shift in the relation between oxygen consumption and pressure-volume area, as previously reported for cooled whole hearts.

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Alpha 1-adrenoceptor subtypes mediating inotropic and electrophysiological effects in mammalian myocardium

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1996.271.4.h1423 ◽

1996 ◽

Vol 271 (4) ◽

pp. H1423-H1432

Author(s):

M. Nagashima ◽

Y. Hattori ◽

Y. Akaishi ◽

N. Tohse ◽

I. Sakuma ◽

...

Keyword(s):

Positive Inotropic Effect ◽

Outward Current ◽

Ventricular Myocardium ◽

Inotropic Effect ◽

Transient Outward Current ◽

Papillary Muscles ◽

Binding Studies ◽

Positive Inotropism ◽

Wb 4101 ◽

Rabbit Ventricular Myocardium

Stimulation of alpha 1-adrenoceptors produces a positive inotropic effect in rat and rabbit ventricular myocardium via different mechanisms, the prolongation of action potential duration (APD) exclusively in the former and an increase in myofibrillar Ca2+ sensitivity in large part in the latter. This study was designed to determine whether the two inotropic mechanisms are mediated by different alpha 1-adrenoceptor subtypes. In rat papillary muscles, the positive inotropic effect and APD prolongation induced by phenylephrine (in the presence of propranolol) were inhibited by WB-4101, but not affected by chlorethylclonidine (CEC). WB-4101, but not CEC, blocked the phenylephrine-induced inhibition of the transient outward current (Ito) in rat ventricular cells. On the other hand, WB-4101 and CEC each antagonized the positive inotropic effect of phenylephrine in rabbit papillary muscles. However, the phenylephrine-induced APD prolongation observed in rabbit papillary muscles was blocked only by WB-4101. These results indicate that the WB-4101 sensitive alpha 1-adrenoceptor subtype mediates the positive inotropism that is correlated with the APD prolongation resulting from Ito reduction, whereas the CEC-sensitive subtype mediates the positive inotropism that is probably associated with increased myofibrillar Ca2+ sensitivity. Radioligand binding studies with [3H] prazosin showed a similar ratio of alpha 1A-to alpha 1B-adrenoceptor subtypes in rat and rabbit ventricular myocardium, implying that the different degree of contribution of each action mechanism to the overall inotropic effect in the two species cannot be explained by distribution of the alpha 1-adrenoceptor subtypes.

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Two mechanisms for positive inotropism of low-K Ringer solution in bullfrog atrium

Nature ◽

10.1038/268755a0 ◽

1977 ◽

Vol 268 (5622) ◽

pp. 755-757 ◽

Cited By ~ 7

Author(s):

MASAYOSI GOTO ◽

YASUO TSUDA ◽

ATSUKO YATANI

Keyword(s):

Ringer Solution ◽

Positive Inotropism ◽

Low K

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Canine coronary venous pressures: responses to positive inotropism and vasodilation

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y83-033 ◽

1983 ◽

Vol 61 (3) ◽

pp. 213-221 ◽

Cited By ~ 7

Author(s):

G. A. Klassen ◽

J. A. Armour

Keyword(s):

Coronary Artery ◽

Arterial Pressure ◽

Venous Pressure ◽

Systolic Pressure ◽

Aortic Occlusion ◽

Venous Tone ◽

Coronary Veins ◽

Artery Pressure ◽

Intramyocardial Pressure ◽

Positive Inotropism

The epicardial coronary venous pressure in 16 dogs was compared with coronary arterial pressure as well as aortic, intraventricular, and intramyocardial pressures. Partial aortic occlusion augmented intraventricular (IVP), intramyocardial (IMP), aortic (AP), and coronary arterial pressures. Peripheral coronary venous pressure was also elevated. Dobutamine significantly augmented IVP and IMP but not aortic or central coronary artery pressures; this agent significantly elevated coronary venous systolic pressure (28/8 to 84/12 mmHg) (1 mmHg = 133.322 Pa). Nitroglycerine decreased IVP, IMP, and AP significantly. Central coronary arterial pressure also fell significantly, but coronary venous pressures remained unchanged. In contrast dipyridamole resulted in no change in IVP, IMP, AP, or coronary arterial systolic pressures; however, the peripheral coronary venous systolic pressure became significantly elevated. Thus the two vasodilators, nitroglycerine and dipyridamole, had different effects upon coronary venous pressure. These data reinforce the recently expressed view that coronary veins behave in a complex fashion and further suggest that their pressures are dependent upon coronary artery pressure, intramyocardial pressure, and coronary venous tone.

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