Existence of functional M3-muscarinic receptors in the human heart.

It has been recently shown that, in adult rat ventricular cardiomyocytes, functional muscarinic receptors (M-receptors) of the M(3)-subtype exist that mediate inositol phosphate (IP) formation. The aim of this study was to characterize the M-receptor subtype mediating IP formation in the human heart. For this purpose in [3H]-myo-inositol labeled slices of human right atria, carbachol-induced [3H]-IP formation and its inhibition by several M-receptor antagonists was assessed. Carbachol (0.1 microM-100 microM) increased [3H]-IP formation; maximal increase at 100 microM was 93+/-16% above basal ( n=20); the pEC(50)-value for carbachol was 5.56. Atropine (1 microM) completely suppressed 100 microM carbachol-induced [3H]-IP formation. Among the M-receptor subtype "selective" antagonists himbacine (1 microM) and pirenzepine (1 microM) only marginally affected carbachol-induced [3H]-IP formation whereas the M(3)-receptor antagonist darifenacin (1 nM-1 microM) concentration-dependently inhibited carbachol-induced [3H]-IP formation with a pK(i)-value of 8.49. We conclude that in human right atrium there exist functional M(3)-receptors that couple to IP formation.

The indirect negative inotropic effect of carbachol in beta1-adrenoceptor antagonist-treated human right atria.

To find out whether indirect negative inotropic effects of carbachol (i.e. decreases in force of contraction that had been stimulated by cyclic AMP-increasing agents) might differ dependent on the agonist employed to increase contractile force in isolated human right atrium, we studied effects of carbachol on atria prestimulated with noradrenaline, terbutaline, histamine and serotonin. All four agonists increased right atrial adenylyl cyclase activity and contractile force, whereby increases for terbutaline, histamine and serotonin, but not for noradrenaline, were significantly larger in right atria from beta(1)-adrenoceptor antagonist-treated vs. non-beta(1)-adrenoceptor antagonist-treated patients. Carbachol (10(-8)-10(-3) M) concentration-dependently decreased agonist-stimulated contractile force: maximum decrease was not significantly different within the four agonists. pD(2) values for carbachol, however, were higher in atria from non-beta(1)-adrenoceptor antagonist-treated vs. beta(1)-adrenoceptor antagonist-treated patients.We conclude that, in isolated human right atria, carbachol-induced indirect negative inotropic effect is not dependent from the agonist employed to increase (via cyclic AMP accumulation) contractile force. However, in atria from beta(1)-adrenoceptor antagonist-treated patients, carbachol-induced indirect negative inotropic effect is attenuated.

Age-dependent changes of cardiac neuronal noradrenaline reuptake transporter (uptake1) in the human heart.

OBJECTIVES: The purpose of this study was to elucidate whether the neuronal noradrenaline reuptake transporter (uptake1) undergoes age-dependent regulation in the human heart. BACKGROUND: Aging is associated with various alterations in cardiovascular function. METHODS: We determined uptake1 density (by [3H]-nisoxetine binding to membranes) and activity (by accumulation of [3H]-noradrenaline into tissue slices) in the right atria (RA) of 42 patients (age range 3 months to 76 years) undergoing open-heart surgery without apparent heart failure. Moreover, the effects of 1 micromol/l desipramine on the noradrenaline-induced positive inotropic effect were assessed in the isolated, electrically driven RA trabeculae of these patients. RESULTS: There was a significant negative correlation between RA uptake1 density and age; moreover, RA uptake1 activity was significantly reduced in elderly patients. Desipramine (1 micromol/l) significantly shifted noradrenaline concentration-response curves to the left; this shift was significantly more pronounced in younger patients than in older patients. CONCLUSIONS: With increasing age, human myocardial uptake1 activity decreases, possibly because of age-dependent downregulation of uptake1 density.

Noradrenaline-induced contraction of human saphenous vein and human internal mammary artery: involvement of different alpha-adrenoceptor subtypes.

Although saphenous veins and internal mammary arteries are commonly used for coronary artery bypass grafting, only a very few comparative studies are available on alpha-adrenoceptor-mediated vasoconstriction in these vessels. Thus, we determined, in isolated rings from human saphenous vein and human internal mammary artery, contractile responses to noradrenaline (10(-8)-10(-4) M) in the absence and presence of the alpha-adrenoceptor antagonists yohimbine (alpha(2)-adrenoceptor antagonist, 10(-8)-10(-6) M), prazosin (alpha(1)-adrenoceptor antagonist, 10(-9)-10(-7) M), 5-methyl-urapidil (5-MU, alpha(1A)-adrenoceptor antagonist, 10(-8)-10(-6) M), BMY 7378 (alpha(1D)-adrenoceptor antagonist, 10(-7)-10(-6) M), and chloroethylclonidine (CEC, irreversible alpha(1B)-adrenoceptor antagonist, 3x10(-5) M for 30 min). All experiments were carried out in the presence of 10(-7) M propranolol and 10(-5) M cocaine. In both vessel types noradrenaline evoked concentration-dependent contractions. In saphenous veins yohimbine was a potent antagonist (pA(2)-value 8.32) while prazosin, 5-MU and BMY exhibited only marginal antagonistic effects. CEC, however, significantly decreased noradrenaline-induced contractions. In contrast, in internal mammary arteries prazosin (pA(2)-value 9.65) and 5-MU (pK(B)-values 7.2-7.5) were potent antagonists, while yohimbine and BMY exhibited only weak antagonistic effects. CEC, however, significantly decreased noradrenaline-induced contractions. We conclude that in saphenous vein the contractile response to noradrenaline is mediated predominantly by alpha(2)-adrenoceptors, while in internal mammary artery it is mediated (to a major part) by alpha(1B)- and (to a minor part) by alpha(1A)-adrenoceptors.