Effect of Ni2+ on the multiphasic positive inotropic responses to histamine mediated by H1-receptors in left atria of guinea pigs

Function and Role of Histamine H1 Receptor in the Mammalian Heart

Histamine can change the force of cardiac contraction and alter the beating rate in mammals, including humans. However, striking species and regional differences have been observed. Depending on the species and the cardiac region (atrium versus ventricle) studied, the contractile, chronotropic, dromotropic, and bathmotropic effects of histamine vary. Histamine is present and is produced in the mammalian heart. Thus, histamine may exert autocrine or paracrine effects in the mammalian heart. Histamine uses at least four heptahelical receptors: H₁, H₂, H₃ and H₄. Depending on the species and region studied, cardiomyocytes express only histamine H₁ or only histamine H₂ receptors or both. These receptors are not necessarily functional concerning contractility. We have considerable knowledge of the cardiac expression and function of histamine H₂ receptors. In contrast, we have a poor understanding of the cardiac role of the histamine H₁ receptor. Therefore, we address the structure, signal transduction, and expressional regulation of the histamine H₁ receptor with an eye on its cardiac role. We point out signal transduction and the role of the histamine H₁ receptor in various animal species. This review aims to identify gaps in our knowledge of cardiac histamine H₁ receptors. We highlight where the published research shows disagreements and requires a new approach. Moreover, we show that diseases alter the expression and functional effects of histamine H₁ receptors in the heart. We found that antidepressive drugs and neuroleptic drugs might act as antagonists of cardiac histamine H₁ receptors, and believe that histamine H₁ receptors in the heart might be attractive targets for drug therapy. The authors believe that a better understanding of the role of histamine H₁ receptors in the human heart might be clinically relevant for improving drug therapy.

The Roles of Cardiovascular H2-Histamine Receptors Under Normal and Pathophysiological Conditions

This review addresses pharmacological, structural and functional relationships among H₂-histamine receptors and H₁-histamine receptors in the mammalian heart. The role of both receptors in the regulation of force and rhythm, including their electrophysiological effects on the mammalian heart, will then be discussed in context. The potential clinical role of cardiac H₂-histamine-receptors in cardiac diseases will be examined. The use of H₂-histamine receptor agonists to acutely increase the force of contraction will be discussed. Special attention will be paid to the potential role of cardiac H₂-histamine receptors in the genesis of cardiac arrhythmias. Moreover, novel findings on the putative role of H₂-histamine receptor antagonists in treating chronic heart failure in animal models and patients will be reviewed. Some limitations in our biochemical understanding of the cardiac role of H₂-histamine receptors will be discussed. Recommendations for further basic and translational research on cardiac H₂-histamine receptors will be offered. We will speculate whether new knowledge might lead to novel roles of H₂-histamine receptors in cardiac disease and whether cardiomyocyte specific H₂-histamine receptor agonists and antagonists should be developed.

Involvement of tyrosine phosphorylation in the positive inotropic effect produced by H(1)-receptors with histamine in guinea-pig left atrium

We investigated the effect of stimulation of H(1)-receptors with histamine on protein tyrosine phosphorylation levels in guinea-pig left atrium and evaluated the influences of tyrosine kinase inhibitors on the positive inotropic effect mediated by H(1)-receptors in this tissue. Histamine induced an increase in tyrosine phosphorylation in four main clusters of proteins with apparent molecular weights of 25, 35, 65 and 150 kDa. Tyrosine phosphorylation of these proteins attained a peak around 2 - 3 min following histamine stimulation and then declined to or below basal levels. Histamine-induced protein tyrosine phosphorylation was antagonized by the H(1)-receptor antagonists mepyramine (1 microM) and chlorpheniramine (1 microM), but not by the H(2)-receptor antagonist cimetidine (10 microM). The positive inotropic effect of histamine was depressed in a concentration-dependent manner by the tyrosine kinase inhibitors tyrphostin A25 (50 to 100 microM) and genistein (10 to 50 microM) but not by the inactive genistein analogue daidzein (50 microM). The positive inotropic effect of isoprenaline was unchanged by tyrphostin A25 and genistein. At a concentration of 1 microM histamine produced a dual-component positive inotropic response composed of an initial increasing phase and a second and late developing, greater positive inotropic phase. Treatment with tyrphostin A25 (100 microM) and genistein (50 microM), but not daidzein (50 microM), significantly attenuated the two components of the inotropic response, although genistein suppressed the initial component more markedly than the late component. We conclude that increased protein tyrosine phosphorylation may play an important role in initiating at least some part of the positive inotropic effect of H(1)-receptor stimulation in guinea-pig left atrium.

Effect of histamine in autoimmune myocarditis mice

The contractile effect of histamine, as well as the H1 receptor population and H2 receptor-mediated cAMP production, were measured in cardiac tissue from control normal and autoimmune myocarditis mice. Histamine triggered positive chronotropy and negative inotropy at high concentrations in both control and autoimmune auricles, H2 receptors being the most important mediator of these responses. In contrast, in atria from autoimmune myocarditis mice, histamine at lower concentrations caused positive inotropy and negative chronotropy. These effects, not verified in the normal control atria, are mediated by H1 receptors. The expression of H2 and H1 receptors mediating the cardiac response to histamine was evaluated through histamine-stimulated cAMP level and binding of [3H] mephyramine, respectively. Both control and autoimmune myocardium were able to increase cAMP levels, an effect that was inhibited by H2 antagonist drug. The amount of cAMP was significantly higher in control myocardium than in those from autoimmune ones. Saturable binding of [3H] mephyramine occurs in autoimmune myocardium, with distinct high and low affinity binding sites. In control myocardium non-saturable binding was detected. These results suggest that H1 and H2 receptors coexist in heart from autoimmune myocarditis mice, whereas only H2 receptors are present in myocardium from control mice. The presence of H1 receptors in autoimmune myocardium could be an important factor in the regulation of its physiological behaviour.

Histamine receptors mediating a positive inotropic effect in guinea pig and rabbit ventricular myocardium: distribution of the receptors and their possible intracellular coupling processes

The difference in histamine receptor subtypes that are involved in the positive inotropic effect of histamine in guinea pig and rabbit ventricular myocardium was analytically characterized. In guinea pig papillary muscles, the positive inotropic effect of histamine was antagonized by cimetidine but not by mepyramine. The converse was true in rabbit papillary muscles. However, histamine evoked a positive inotropic effect through H1- and H2-receptors after blockade of H2- and H1-receptors in guinea pig and rabbit papillary muscles, respectively. Adenylate cyclase was significantly activated by histamine via H2-receptors in guinea pig but not in rabbit myocardial ventricular membranes. Accumulation of [3H]inositol monophosphate in ventricular strips prelabeled with myo-[3H]inositol was increased by histamine via H1-receptors to a similar extent in rabbits and guinea pigs. Radioligand binding experiments with [3H]mepyramine and [3H]tiotidine showed an increased number of H1-receptors and a decreased number of H2-receptors in guinea pig compared with rabbit ventricular myocardium. These results suggest that the positive inotropic effects of histamine are dominated by an H1-receptor-mediated effect in rabbits and by an H2-receptor-mediated one in guinea pig ventricular myocardium, and the positive inotropic effect manifested by one subtype apparently restricts the expression of the positive inotropic effect mediated by the other subtype. This species difference is not due to a difference in densities of the receptor subtypes, but may be partly related to a difference in the extents of coupling of H2-receptors to adenylate cyclase.

Altered cardiac adrenergic neurotransmission in streptozotocin-induced diabetic rats

1. Functional alterations of the sympathetic neuroeffector junction of the left atria were studied in rats with streptozotocin-induced diabetes. 2. Eight to 12 weeks of diabetes resulted in a marked decrease in the positive inotropic response of left atria to electrical field stimulation (EFS). 3. The overflow of [3H]-noradrenaline from diabetic left atria caused by EFS was much less than that from control preparations. 4. The concentration-response curves showed no change in sensitivities of the left atria to exogenous noradrenaline and tyramine in diabetic rats. The maximum positive inotropic response to these agents were similar in diabetic and control animals. 5. The left atrial content of noradrenaline was not significantly changed in diabetic rats. The cocaine-sensitive uptake of [3H]-noradrenaline was also unaltered. 6. Atropine enhanced the positive inotropic response and [3H]-noradrenaline overflow induced by EFS in control left atria. Similarly, yohimbine caused an enhancement of EFS-evoked inotropic response in control atria. However, these effects of the antagonists were not observed in diabetic left atria. 7. It is concluded that the decrease in the positive inotropic response of the left atria to EFS in diabetic rats is caused by an impairment of noradrenaline release from the sympathetic nerve terminals through a calcium-dependent exocytotic mechanism. The present results also indicate that presynaptic alpha 2-adrenoceptors and muscarinic receptors that are linked to inhibition of the noradrenaline release during nerve stimulation may be functionally impaired in diabetic animals.

Identification and characterization of histamine H1- and H2-receptors in guinea-pig left atrial membranes by [3H]-mepyramine and [3H]-tiotidine binding

1. Histamine receptors in the membranes prepared from guinea-pig left atria were characterized with [3H]-mepyramine and [3H]-tiotidine binding. 2. The binding of the H1-antagonist, [3H]-mepyramine, was saturable and of high affinity with a maximum binding capacity of 307 +/- 27 fmol mg-1 protein (n = 14) and with an equilibrium dissociation constant (KD) of 1.5 +/- 0.2 nM (n = 14). The binding was rapid and readily reversible. 3. The competition curve for [3H]-mepyramine binding by histamine was biphasic and revealed high and low affinity states of binding. The addition of 5'-guanylylimidodiphosphate (GppNHp) (100 microM) converted this heterogeneous binding into homogeneous binding of low affinity. 4. The competition curves of H1-antagonists with [3H]-mepyramine had Hill coefficients not significantly different from unity, consistent with competition with [3H]-mepyramine at a single site. GppNHp did not shift the competition curves. 5. Dissociation constants for H1-antagonists determined from inhibition of [3H]-mepyramine binding correlated well with the constants derived from inhibition of the positive inotropic response of guinea-pig left atria to histamine. 6. The H2-antagonist, [3H]-tiotidine, labelled an apparently homogeneous population of recognition sites with a maximum binding capacity of 41 +/- 8 fmol mg-1 protein (n = 6) and a KD of 10.8 +/- 1.2 nM (n = 6). 7. Although histamine competed for [3H]-tiotidine binding in a concentration-dependent manner, the curve was monophasic and was not shifted by GppNHp. 8. It is concluded that both H1- and H2-receptors exist in guinea-pig left atria. H1-receptors probably couple to intracellular effector(s) through a guanine nucleotide-dependent transducing mechanism. On the other hand, H2-receptors seem unlikely to be linked to guanine nucleotide regulatory proteins in guineapig left atria, which may explain the failure of histamine to cause an increase in cyclic AMP in spite of the presence of H2-receptors.

Characterization of histamine receptors modulating inotropic and biochemical activities in rabbit left atria

The experiments were performed to identify histamine H1- and H2-receptors in rabbit left atrium and to characterize the pharmacological properties mediated by the respective subtypes of histamine receptors. High-affinity saturable binding to the left atrial membranes was obtained for [3H]mepyramine, yielding a maximum binding capacity (Bmax) of 96 fmol/mg of protein and an equilibrium dissociation constant (KD) of 3.8 nM and also for [3H]tiotidine, yielding a Bmax of 126 fmol/mg of protein and a KD of 14.7 nM. In isolated left atrium, histamine produced a concentration-dependent positive inotropic effect, an effect which was competitively antagonized by cimetidine but not altered by chlorpheniramine. Schild analysis showed that the pA2 value for cimetidine was 6.55 and the slope was not significantly different from unity. An excellent correlation was found between the increase in force of contraction and cyclic AMP in the presence of histamine, suggesting that the positive inotropic effect of histamine in rabbit left atrium is dependent on an increased level of intracellular cyclic AMP through stimulation of histamine H2-receptors. Histamine also produced concentration-dependent stimulation of phosphoinositide hydrolysis as measured by [3H]inositol monophosphate accumulation. The phosphoinositide response to histamine was blocked by chlorpheniramine and mepyramine but not by cimetidine. The data indicate that histamine H1-receptors, in addition to histamine H2-receptors, are present in the rabbit left atrium. Although this tissue lacks an inotropic response to histamine H1-receptor stimulation, the histamine H1-receptors interact with histamine to mediate the stimulation of phosphoinositide hydrolysis.

Comparison of the responses to light and to GABA of cells postsynaptic to barnacle photoreceptors (I-cells)

We tested the hypothesis that gamma-aminobutyric acid (GABA) is the transmitter released by barnacle photoreceptors onto postsynaptic cells (I-cells). GABA was applied to I-cells either by superfusion or by ejecting it with pressure from a pipette positioned close to the I-cell's soma. The I-cell's response to GABA was compared with its response to light (i.e. to the photoreceptors' transmitter) by recording intracellularly from its soma. Bath-applied (100 microns to 10 mM) and pressure-applied GABA (10 mM in pipette) hyperpolarizes I-cells by increasing their conductance, as does the photoreceptors' transmitter. The response to pressure-applied GABA consists of two components; both persist when Co2+ or Cd2+ are added to the saline to block synaptic transmission in the preparation, indicating that GABA affects the I-cell directly rather than affecting a presynaptic cell. GABA hyperpolarizes the I-cell when applied to the cell over the soma and ipsilateral arbor or over the contralateral arbor. The I-cells' responses to GABA and to light both depend on extracellular K+ and are affected by changes in intracellular and extracellular Cl-. However, picrotoxin and beta-guanidinopropionic acid block the response to pressure-applied GABA but do not block the response to light even at an order of magnitude higher concentration. Thus, GABA is not likely to be the transmitter that causes the hyperpolarizing response of the I-cell. It may be a neuromodulator or the transmitter of an unknown input to the I-cell.

Differential effects of histamine mediated by histamine H1- and H2-receptors on contractility, spontaneous rate and cyclic nucleotides in the rabbit heart

The effects of histamine on the contractile force, spontaneous rate of contraction, and cyclic AMP and cyclic GMP content were investigated in isolated rabbit cardiac preparations. Histamine had a positive inotropic effect in the left atrium and papillary muscle, and a positive chronotropic effect in the right atrium. Both effects were produced in a concentration-dependent manner. Impromidine also induced the same effect in the left and right atrium as histamine did. The effects produced by histamine and impromidine were antagonized by cimetidine and tiotidine. On the other hand, the positive inotropic response of papillary muscle to histamine was antagonized by mepyramine and chlorpheniramine and was mimicked by 2-(2-pyridyl)ethylamine. Impromidine at a high concentration induced a small increase in the contractile force, an effect which was antagonized by cimetidine. Histamine significantly increased the cyclic AMP levels in both atria but not in papillary muscles. The increase in cyclic AMP was abolished by cimetidine. Histamine also increased cyclic GMP levels in all of the preparations. The increase in cyclic GMP was abolished by chlorpheniramine. The results suggest that both H1- and H2-receptors exist in all parts of the rabbit heart. However, the positive inotropic and chronotropic effects induced by histamine in left and right atrium are mediated predominantly via H2-receptors, whereas the positive inotropic effect in papillary muscle is predominantly mediated via H1 receptors.

Effects of Ca2+ channel antagonists and ryanodine on H1-receptor mediated electromechanical response to histamine in guinea-pig left atria

Effects of organic Ca2+ channel antagonists, Ni2+ and ryanodine on the electrophysiological and positive inotropic responses to histamine were examined in isolated guinea-pig left atria. Histamine increased force of contraction, prolonged action potential duration (APD) and hyperpolarized the membrane in a concentration-dependent manner. Histamine at a concentration of 1 mumol/l produced a dual-component positive inotropic response composed of an initial increasing phase (initial component) and a second and late developing, greater positive inotropic phase (second component), whereas causing monophasic changes in APD and resting potential. The electrophysiological and dual-component positive inotropic effects induced by histamine were antagonized by chlorpheniramine (1 mumol/l) but not by cimetidine (10 mumol/l), indicating that both effects are exclusively mediated by H1-receptors. The positive inotropic response to 1 mumol/l histamine was changed by the pretreatment with nifedipine (1 mumol/l) and nisoldipine (1 mumol/l). In the presence of these dihydropyridines, the second component was almost completely abolished, while the initial component was hardly affected. On the other hand, verapamil (3 mumol/l) and diltiazem (10 mumol/l) failed to modify the multiphasic inotropic response to histamine. None of the Ca2+ channel antagonists affected the histamine-induced APD prolongation. In the presence of Ni2+ at a concentration of 0.3 mmol/l, at which it produced no negative inotropic action, the second component of the positive inotropic effect of histamine was specifically suppressed whereas the histamine-induced APD prolongation was unaffected. Preferential attenuation of the second component was also observed in the presence of 30 nmol/l ryanodine.(ABSTRACT TRUNCATED AT 250 WORDS)