Nonadrenergic noncholinergic nerves regulate basal coronary flow via release of capsaicin-sensitive neuropeptides in the rat heart

Cardiac innervations in diabetes mellitus-Anatomical evidence of neuropathy

The extensive innervations of the heart include a complex network of sympathetic, parasympathetic, and sensory nerves connected in loops that serve to regulate cardiac output. Metabolic dysfunction in diabetes affects many different organ systems, including the cardiovascular system; it causes cardiac arrhythmias, silent myocardial ischemia, and sudden cardiac death, among others. These conditions are associated with damage to the nerves that innervate the heart, cardiac autonomic neuropathy (CAN), which is caused by various pathophysiological mechanisms. In this review, the main facts about the anatomy of cardiac innervations and the current knowledge of CAN, its pathophysiological mechanisms, and its diagnostic approach are discussed. In addition, anatomical evidence for CAN from human and animal studies has been summarized.

Cardiopulmonary function and dysregulated cardiopulmonary reflexes following acute oleoresin capsicum exposure in rats

Cardiopulmonary functions such as respiratory depression, severe irritation, inflamed respiratory tract, hyperventilation and, tachycardia are the most affected ones when it comes to the riot control agent oleoresin capsicum (OC) exposure. However, no studies have been done to elucidate the mechanism underlying deterioration of the combined cardiopulmonary functions. Parameters such as acute respiratory, cardiac, parameters and ultrasonography (USG) measurements were investigated in an in vivo setup using Wistar rats at 1 h and 24 h post inhalation exposure to 2%, 6% and 10% OC, whereas, cell migration in rat peritoneal mast cells (RPMCs), metabolomics and eosinophil peroxidase (EPO) activity in bronchoalveolar lavage fluid (BALF) were investigated in an in vitro setup. Results obtained from electrophysiological recording indicated that OC exposure produces apnea and decrease in mean arterial pressure (MAP) was obtained from hemodynamic parameters whereas cardiac parameters assessment revealed increase in the level of cardiac output (CO) and decrease in stroke volume (SV) with recovery towards the post-exposure period. A decrease in the percentage area of certain fatty acid pathway metabolites in BALF appropriately linked the lung injury following OC exposure which was further cemented by increasing concentration of EPO. Histopathology and SEM also proved to be favorable techniques for the detection of OC induced physiological cardiac and pulmonary modifications respectively. Furthermore, Boyden chamber experiment established the chemoattractant property of OC. It may be concluded from the above studies that these newly reported facets may be utilized pharmacologically to mitigate cardiopulmonary adverse effects owing to OC exposure.

Heteroreceptors Modulating CGRP Release at Neurovascular Junction: Potential Therapeutic Implications on Some Vascular-Related Diseases

Calcitonin gene-related peptide (CGRP) is a 37-amino-acid neuropeptide belonging to the calcitonin gene peptide superfamily. CGRP is a potent vasodilator with potential therapeutic usefulness for treating vascular-related disease. This peptide is primarily located on C- and Aδ-fibers, which have extensive perivascular presence and a dual sensory-efferent function. Although CGRP has two major isoforms (α-CGRP and β-CGRP), the α-CGRP is the isoform related to vascular actions. Release of CGRP from afferent perivascular nerve terminals has been shown to result in vasodilatation, an effect mediated by at least one receptor (the CGRP receptor). This receptor is an atypical G-protein coupled receptor (GPCR) composed of three functional proteins: (i) the calcitonin receptor-like receptor (CRLR; a seven-transmembrane protein), (ii) the activity-modifying protein type 1 (RAMP1), and (iii) a receptor component protein (RCP). Although under physiological conditions, CGRP seems not to play an important role in vascular tone regulation, this peptide has been strongly related as a key player in migraine and other vascular-related disorders (e.g., hypertension and preeclampsia). The present review aims at providing an overview on the role of sensory fibers and CGRP release on the modulation of vascular tone.

Neonatal capsaicin administration impairs postnatal development of the cardiac chronotropy and inotropy in rats

The present study evaluated the impact of neonatal administration of capsaicin (neurotoxin from red hot pepper used for sensory denervation) on postnatal development of the heart rate and ventricular contractility. In the rats subjected to capsaicin administration (100 mg/kg) on postnatal days 2 and 3 and their vehicle-treated controls at the ages of 10 to 90 days, function of the sympathetic innervation of the developing heart was characterized by evaluation of chronotropic responses to metipranolol and atropine, norepinephrine concentrations in the heart, and norepinephrine release from the heart atria. Sensory denervation was verified by determination of calcitonin gene-related peptide levels in the heart. Direct cytotoxic effects of capsaicin were assessed on cultured neonatal cardiomyocytes. Capsaicin-treated rats displayed higher resting heart rates, lower atropine effect, but no difference in the effect of metipranolol. Norepinephrine tissue levels and release did not differ from controls. Contraction force of the right ventricular papillary muscle was lower till the age of 60 days. Significantly reduced viability of neonatal cardiomyocytes was demonstrated at capsaicin concentration 100 micromol/l. Our study suggests that neonatal capsaicin treatment leads to impaired maturation of the developing cardiomyocytes. This effect cannot be attributed exclusively to sensory denervation of the rat heart since capsaicin acts also directly on the cardiac cells.

Neurocardiology: Structure-Based Function

Cardiac control is mediated via a series of reflex control networks involving somata in the (i) intrinsic cardiac ganglia (heart), (ii) intrathoracic extracardiac ganglia (stellate, middle cervical), (iii) superior cervical ganglia, (iv) spinal cord, (v) brainstem, and (vi) higher centers. Each of these processing centers contains afferent, efferent, and local circuit neurons, which interact locally and in an interdependent fashion with the other levels to coordinate regional cardiac electrical and mechanical indices on a beat-to-beat basis. This control system is optimized to respond to normal physiological stressors (standing, exercise, and temperature); however, it can be catastrophically disrupted by pathological events such as myocardial ischemia. In fact, it is now recognized that autonomic dysregulation is central to the evolution of heart failure and arrhythmias. Autonomic regulation therapy is an emerging modality in the management of acute and chronic cardiac pathologies. Neuromodulation-based approaches that target select nexus points of this hierarchy for cardiac control offer unique opportunities to positively affect therapeutic outcomes via improved efficacy of cardiovascular reflex control. As such, understanding the anatomical and physiological basis for such control is necessary to implement effectively novel neuromodulation therapies. © 2016 American Physiological Society. Compr Physiol 6:1635-1653, 2016.

Translational neurocardiology: preclinical models and cardioneural integrative aspects

Neuronal elements distributed throughout the cardiac nervous system, from the level of the insular cortex to the intrinsic cardiac nervous system, are in constant communication with one another to ensure that cardiac output matches the dynamic process of regional blood flow demand. Neural elements in their various 'levels' become differentially recruited in the transduction of sensory inputs arising from the heart, major vessels, other visceral organs and somatic structures to optimize neuronal coordination of regional cardiac function. This White Paper will review the relevant aspects of the structural and functional organization for autonomic control of the heart in normal conditions, how these systems remodel/adapt during cardiac disease, and finally how such knowledge can be leveraged in the evolving realm of autonomic regulation therapy for cardiac therapeutics.

Non-excitatory electrical stimulation attenuates myocardial infarction via homeostasis of calcitonin gene-related peptide in myocardium

Electrical stimulation has been shown protection of brain, retina, optic nerves and pancreatic β-cells but the effect on cardio-protection is still unknown. Calcitonin gene-related peptide (CGRP) participates in the pathology of injury and protection of myocardium but whether or not electrical stimulation modulates endogenous CGRP is not clear. Male Sprague-Dawley rats were divided into 4 groups: (1) control group, without any treatment. (2) I/R group, animals were subjected to 30 min of myocardial ischemia followed by 60 min reperfusion. (3) NES+I/R group, non-excitatory electrical stimulation (NES) was commenced from 15 min before coronary artery occlusion till the end of reperfusion. (4) I/R+CGRP8-37 group, animals were given with CGRP8-37 (an antagonist of CGRP receptor, 10(-7) mol/L, 0.3 ml, i.v.) at 5 min before reperfusion without any electrical stimulation. The hemodynamics and electrocardiogram were monitored and recorded. Infarct size and troponin I were examined and CGRP expression in the myocardium and serum was analyzed. It was found that the infarct size and TnI were significantly reduced in NES+I/R group, by 45% and 58% respectively, accompanied by an obvious fall back of CGRP in myocardium, compared to I/R group (all p<0.05). Treatment with CGRP8-37 resulted in the same protection on myocardium as NES did. No significant difference in hemodynamics or ventricular tachycardia was detected among the groups (all p>0.05). It can be concluded that NES reduced the infarction size after acute myocardial ischemia and reperfusion, for which the underlying mechanism may be associated with modulation of endogenous CGRP in myocardium.

Inhibitor Effect of Antioxidant Flavonoids Quercitin, and Capsaicin in Mast Cell Inflammation

Mast cells are essential not only for allergies but also for innate and acquired immunity, autoimmunity and inflammation, and they are recognized as a new type of immunoregulatory cells capable of producing different cytokines. Natural compounds have long been recognized to possess anti-inflammatory, antioxidant and anticancergenic activity. Quercitin is an inhibitor for mast cells and is a potent antioxidant, cytoprotective and anti-inflammatory compound and has a negative effect on intracellular regulator signal events initiated by FceRI receptor cross-linking and other activating receptors on mast cells. These observations candidate quercitin as a therapeutic compound in association with other therapeutic molecules. Capsaicin is a compound derived from peppers, especially capsicum, and is involved in stimulating circulation aiding digestion and relieving pain. Capsaicin receptor sub type I (VRI) is expressing in neurons and is present in a number of brain nuclei and in non-neuronal tissues, mediating inflammatory response. Capsaicin is involved in migraine, allergic symptoms, arthritis pain and gastric secretion. In this paper we review the biological effects of quercitin and capsaicin.

Gender-specific effects of calcitonin gene-related peptide and substance P on coronary blood flow in an experimental model

BACKGROUND

Calcitonin gene-related peptide (CGRP) and substance P (SP) play counter-regulatory roles in coronary flow. This study is to assess whether effects of CGRP and SP are gender-specific.

METHODS

Langendorff-perfused hearts were used to compare coronary flow rates among 119 wild-type, alpha-CGRP and SP receptor knockout mice under various perfusion pressures (20, 30, 40, 50 mmHg).

RESULTS

For mouse heart coronary flow rate, deletion of alpha-CGRP gene resulted in significant reduction for both genders at all pressures; female CGRP knockout showed 15.3% reduction (P < .01); male CGRP knockout showed 13.8% reduction (P < .01); no significant difference between male and female CGRP knockout; female SP receptor knockout showed 13.9% increase (P < .01); female SP receptor knockout had a greater percentage decrease than male (P < .01).

CONCLUSIONS

CGRP plays similar roles as a vasodilator in males and females. SP seems to act as a vasoconstrictor in females.

Mechanisms involved in calcitonin gene-related Peptide-induced relaxation in pregnant rat uterine artery

Human and rodent studies have demonstrated that calcitonin gene-related peptide (CGRP), a potent vasodilator, relaxes uterine tissue during pregnancy but not during labor. The vascular sensitivity to CGRP is enhanced during pregnancy, compared to nonpregnant human uterine arteries. In the present study, we hypothesized that uterine artery relaxation effects of CGRP are enhanced in pregnant rats compared to nonpregnant diestrus rats (NP-DE) and that several secondary messenger systems are involved in this process. We also hypothesized that the expression of CGRP-A receptor components, calcitonin receptor-like receptor (CRLR), receptor activity-modifying protein (RAMP1), and CGRP-B receptors are greater in pregnant rats. For vascular relaxation studies, uterine arteries from either NP-DE or Day 18 pregnant rats were isolated, and responsiveness of the vessels to CGRP was examined with a small vessel myograph. CGRP-A and CGRP-B receptor expressions were assessed by RT-PCR and Western immunoblotting, respectively. CGRP (10(-10)--10(-7) M) produced a concentration-dependent relaxation of norepinephrine-induced contractions in both NP-DE and Day 18 pregnant rat uterine arteries. Pregnancy increased the vasodilator sensitivity to CGRP significantly (P < 0.05) compared to NP-DE rats. CGRP receptor antagonist, CGRP8-37, inhibited CGRP-induced relaxation of pregnant uterine arteries. The CGRP-induced relaxation was not affected by NG-nitro-l-arginine methyl ester (L-NAME) (nitric oxide inhibitor, 10(-4) M) but was significantly (P < 0.05) attenuated by inhibitors of guanylate cyclase (ODQ, 10(-5) M) and adenylate cyclase (SQ 22536, 10(-5) M). CGRP-induced vasorelaxation was significantly (P < 0.05) attenuated by potassium channel blockers KATP (glybenclamide, 10(-5) M) and K(CA) (tetraethylammonium, 10(-3) M). The expression of CRLR and RAMP1 was significantly (P < 0.05) elevated during pregnancy compared to nonpregnant diestrus state (NP-DE). However, CGRP-B receptor proteins in uterine arteries were not altered with pregnancy compared to those of NP-DE. These studies suggest that CGRP-induced increases in uterine artery relaxation may play a role in regulating blood flow to the uterus during pregnancy and, therefore, in fetal growth and survival.

Effects of Inhibition of α-CGRP Receptors on Cardiac and Peripheral Vascular Dynamics in Conscious Dogs with Chronic Heart Failure

Whether endogenous calcitonin gene-related peptide (CGRP) plays a role in heart failure is unclear. Seven dogs were instrumented with left ventricular (LV) pressure gauges, pacers, coronary occluder and aortic, atrial, and coronary sinus catheters. Hemodynamic recordings and response to alpha-CGRP challenge were obtained for baseline in the conscious state. Rapid pacing (240 beats/min) was then initiated. The coronary artery was occluded for 90 minutes followed by reperfusion after 2 weeks of pacing. After 6 weeks of pacing, LV pressure (-11 +/- 6%), LV dP/dt (-53 +/- 5%), and mean arterial pressure (-15 +/- 4%) decreased (P < 0.01), while left atrial pressure (+19 +/- 3 mm Hg from 7 +/- 1 mm Hg) and heart rate (+53 +/- 16%) increased (P < 0.01). Infusion of the alpha-CGRP receptor antagonist alpha-CGRP[8-37] (30 microg/kg/min, i.v.), which blocked the exogenous alpha-CGRP challenge, did not affect any of these indices. Regional blood flow, as measured by the microsphere technique, in the nonischemic myocardium, as well as cerebral and renal vasculatures were unaltered during the infusion of alpha-CGRP[8-37]. Plasma concentrations of CGRP from both arterial and coronary sinus samples were unchanged after 6 weeks of pacing as compared with control. Thus, we conclude that endogenous alpha-CGRP does not appear to play a major role in the regulation of cardiac and peripheral vascular dynamics in the late stage of heart failure.

Topographic morphology and age-related analysis of the neuronal number of the rat intracardiac nerve plexus

The study was designed to determine the three-dimensional organization of the rat intrinsic cardiac neural plexus (ICNP) and to ascertain whether the rat heart undergoes a decrease in neuronal number with aging as has been reported for other mammalian species, including human. Juvenile (3-4 weeks of age, n = 14) and adult (more than 2 months of age, n = 23) animals were examined using enzyme histochemistry for acetylcholinesterase in order to visualize the ICNP in total hearts. The number of intrinsic cardiac neurons was estimated by counting nerve cells in serial sections of the atrial pieces stained with cresyl fast violet. The total number of intrinsic cardiac neurons in old rats was 6576 +/- 317. The juvenile animals contained significantly fewer such neurons, only 5009 +/- 332. Approximately 70% of all intracardiac neurons were amassed within the heart hilum, while 30% of the neurons were distributed epicardially. Within the interatrial septum, only 11 +/- 11 neurons were identified in the juvenile and 6 +/- 4 neurons in old rats. Extrinsic nerves entered the rat heart in both the arterial and venous parts of the cardiac hilum. The nerves from the arterial part of the cardiac hilum extended directly to the ventricles but the nerves from the venous part of the hilum formed a particular nerve plexus of the cardiac hilum on the heart base. Within the rat epicardium, intrinsic nerves clustered into six routes by which they selectively projected to different atrial and/or ventricular regions. In conclusion, this study provides a detailed description of the three-dimensional organization of the rat ICNP and contradicts the decrease in neuronal number with aging in the rat heart.

Calcitonin gene-related peptide in pregnancy and its emerging receptor heterogeneity

Calcitonin gene-related peptide (CGRP) is the most potent vasodilator, and there is a growing body of evidence that this peptide might have multiple other functions. During pregnancy, circulating CGRP levels in rats increase up to the time of delivery, followed by a sharp decline at term and postpartum. In addition, the sensitivity of various vascular beds to CGRP in rats appears to increase with advancing pregnancy. This increased sensitivity might be involved in regulating uteroplacental blood flow, in addition to other vascular adaptations that occur during normal pregnancy. Furthermore, the uterine relaxation response to CGRP is elevated during pregnancy and decreased at term. Sex steroid hormones, estrogens and progesterone, regulate CGRP synthesis and its effects on both myometrial and uterine vascular tissues. These changes in smooth muscle relaxation sensitivity to CGRP appear to be a consequence of changes in CGRP-receptor levels in these tissues. There appear to be two receptors for CGRP: the CGRP-A receptor, a well-characterized receptor consisting of calcitonin receptor-like receptor and receptor activity modifying protein 1, and the CGRP-B receptor. The CGRP system might play a role in the maintenance of normal pregnancy, and a defect in this system might lead to complications.

Influence of calcitonin gene-related peptide release on pH-induced mechanical depression in rat atria

Rat atria is richly innervated by sensory nerve fibers that release CGRP when stimulated either by capsaicin or acid pH. We studied the physiological relevance of acid pH-induced CGRP release on changes in atrial contractility and relaxation produced by lowering the pH. Isolated atria electrically paced at 2.77 Hz were exposed to a 10-minute period of metabolic acidosis (pH=6.73+/-0.01, n=28) after: 1) CGRP release induced by capsaicin 0.5 microM; 2) blockage of CGRP release with ruthenium red (RR) 5 microM; 3) no pretreatment; and 4) CGRP receptor blockage with CGRP(8-37) 1 microM. Contractility and relaxation were significantly less depressed by acid pH when CGRP release was prevented by RR or CGRP receptor activation was blocked by CGRP(8-37). The results suggest that CGRP release and the activation of CGRP receptors may be physiologically involved in contributing to the depression of contractility and relaxation induced by acid pH in rat atria.

Vasoactive intestinal polypeptide and calcitonin gene-related peptide in the developing rat heart atria

Vasoactive intestinal polypeptide-like immunoreactivity (VIP-LI) and calcitonin gene-related peptide (CGRP)-LI concentrations were determined in the developing rat heart atria using radioimmunoassay. Peptide levels were analysed on postnatal days 1, 10, 25, 45, 60, and 85 (P1-P85) separately in the right (RA) and left atria (LA). No sex differences were revealed at any age examined. VIP-LI has been already detected in both atria at P1 in concentrations comparable to values at P10. In the RA, VIP-LI levels increased significantly between days P10 and P25, remained high at P45 and then declined. In the LA, VIP-LI concentrations did not differ from those in the RA on days P1, P10, P25, and P45. However, regional differences were found at P60 and P85, when the peptide levels were significantly higher in the LA than in the RA. The postnatal changes in CGRP-LI concentrations were comparable in both atria with similar values at P1 and P85. After birth, CGRP levels decreased gradually till P45, then they increased till P60 and declined again at P85. The results demonstrate that there is an asymmetry in the postnatal development of the atrial VIP-LI and CGRP-LI concentrations. VIP-LI levels reached their maximum at P25, whereas CGRP-LI levels at P60. Relatively high peptide concentrations in neonatal atria and their variations during development might be related to diverse trophic functions of VIP and CGRP.

Coronary microcirculation: physiology and pharmacology

Coronary microvessels play a pivotal role in determining the supply of oxygen and nutrients to the myocardium by regulating the coronary flow conductance and substance transport. Direct approaches analyzing the coronary microvessels have provided a large body of knowledge concerning the physiological and pharmacological characteristics of the coronary circulation, as has the rapid accumulation of biochemical findings about the substances that mediate vascular functions. Myogenic and flow-induced intrinsic vascular controls that determine basal tone have been observed in coronary microvessels in vitro. Coronary microvascular responses during metabolic stimulation, autoregulation, and reactive hyperemia have been analyzed in vivo, and are known to be largely mediated by metabolic factors, although the involvement of other factors should also be taken into account. The importance of ATP-sensitive K(+) channels in the metabolic control has been increasingly recognized. Furthermore, many neurohumoral mediators significantly affect coronary microvascular control in endothelium-dependent and -independent manners. The striking size-dependent heterogeneity of microvascular responses to all of these intrinsic, metabolic, and neurohumoral factors is orchestrated for optimal perfusion of the myocardium by synergistic and competitive interactions. The regulation of coronary microvascular permeability is another important factor for the nutrient supply and for edema formation. Analyses of collateral microvessels and subendocardial microvessels are important for understanding the pathophysiology of ischemic hearts and hypertrophied hearts. Studies of the microvascular responses to drugs and of the impairment of coronary microvessels in diseased conditions provide useful information for treating microvascular dysfunctions. In this article, the endogenous regulatory system and pharmacological responses of the coronary circulation are reviewed from the microvascular point of view.

Contribution of nitric oxide and sensory transmitters to non-adrenergic, non-cholinergic innervation of nasal blood vessels

The possible contribution of a non-adrenergic, non-cholinergic (NANC) vasodilator mechanism in human nasal mucosa was studied using an in vitro muscle tension measuring technique. Strips of the nasal mucosa were suspended in a Magnus tube filled with Krebs solution and aerated with 95% O2. Isometric changes in tension were detected on administration of various drugs under electric stimulation and recorded with a transducer. The relaxing reaction under electrical train pulse stimulation with pretreatment of blockers of the autonomic nerves was suppressed by nitric oxide synthase inhibitor (L-NAME) and antagonists to the receptors of sensory nerve transmitters (Spantide, hCGRP8-37). This result suggests that nitric oxide, substance P and CGRP may be mediators in the NANC inhibitory nerve system.

Interaction between capsaicin and nitrate tolerance in isolated guinea-pig heart

Capsaicin-induced increases in heart rate and coronary flow were blocked by N(G)-nitro-L-Arg-methyl ester (30 mM) in Langendorff-perfused guinea-pig hearts. Neither heart rate nor coronary flow changed by capsaicin in hearts from animals made tolerant to the hypotensive effect of 30 microg/kg nitroglycerin by the administration of 50 mg/kg nitroglycerin subcutaneously 4 times a day over 3 days. We conclude that the effector function of sensory nerves may deteriorate in nitrate tolerance.

Aggravation of myocardial infarction in the porcine heart by capsaicin-induced depletion of calcitonin gene-related peptide (CGRP)

The potent vasodilator calcitonin gene-related peptide (CGRP) is stored in a population of C-fiber afferents that are sensitive to capsaicin. CGRP has been suggested to have a beneficial effect in myocardial ischemia. In this study we used capsaicin pretreatment to deplete cardiac C-fiber peptide stores and tried to evaluate the role of endogenous CGRP in myocardial ischemia. Six pigs were pretreated with capsaicin (50 mg/kg). Forty-eight hours later, they were subjected to 40min occlusion of the left anterior descending coronary artery. After 4 h of reperfusion, the heart was excised, and the extent of myocardial infarction was measured by using triphenyl tetrazolium chloride. Content of CGRP in the ischemic and the nonischemic myocardium was measured by radioimmunoassay. Capsaicin-treated pigs had more extensive myocardial infarction (56+/-6% vs. 26+/-8% of the area at risk; p=0.013) and a lower myocardial content of CGRP (14+/-6 vs. 32+/-5 pmol/g; p=0.039) compared with six untreated control pigs. Furthermore, capsaicin-treated pigs had significantly increased mean arterial blood pressure compared with controls. This study indicates that peptides released from cardiac C fibers have a beneficial effect in myocardial ischemia and reperfusion. In view of its potent effects in cardiovascular regulation, CGRP is a possible candidate for the mediation of the observed cardioprotective effect.

ATP-sensitive K+ channel activation by calcitonin gene-related peptide and protein kinase A in pig coronary arterial smooth muscle

1. We used patch clamp to study whole-cell K+ currents activated by calcitonin gene-related peptide (CGRP) in smooth muscle cells freshly dissociated from pig coronary arteries. 2. CGRP (50 nM) activated an inward current at -60 mV in symmetrical 140 mM K+ that was blocked by glibenclamide (10 microM), an inhibitor of ATP-sensitive potassium (KATP) channels. CGRP-induced currents were larger in cells dialysed with 0.1 mM ATP than with 3.0 mM ATP. 3. Forskolin (10 microM) activated a glibenclamide-sensitive current, as did intracellular dialysis with cAMP (100 microM). The catalytic subunit of cAMP-dependent protein kinase (protein kinase A, PKA), added to the pipette solution, activated equivalent currents in five out of twelve cells. 4. CGRP-induced currents were reduced by the PKA inhibitors adenosine 3',5'-cyclic monophosphorothioate, RP-isomer, triethylammonium salt (Rp-cAMPS; 100 microM) and N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulphonamide+ ++ dihydrochloride (H-89; 1 microM), and abolished by inclusion of a PKA inhibitor peptide in the pipette solution. 5. The beta-adrenergic agonist isoprenaline (10 microM) also activated a glibenclamide-sensitive K+ current. 6. CGRP-induced currents were unaffected by the inhibitor of cGMP-dependent protein kinase (PKG) KT5823 (1 microM). Sodium nitroprusside (10 microM) did not activate a glibenclamide-sensitive current in cells held at -60 mV, but did activate an outward current at +60 mV that was abolished by KT5823, or by 100 nM iberiotoxin (an inhibitor of BKCa channels). 7. Our findings suggest that CGRP activates coronary KATP channels through a pathway that involves adenylyl cyclase and PKA, but not PKG.

Involvement of ATP in the non-adrenergic non-cholinergic inhibitory neurotransmission of lamb isolated coronary small arteries

1. The involvement of non-adrenergic non-cholinergic (NANC) transmitters, such as nitric oxide (NO) and adenosine 5'-triphosphate (ATP), in the neurogenic relaxation of lamb coronary small arteries was investigated in vessel segments with an internal lumen diameter of 200-550 microns, isolated from the left ventricle of the heart, and suspended for isometric tension recording in microvascular myographs. 2. In both endothelium-intact and -denuded coronary small arteries treated with phentolamine (3 x 10(-6) M), propranolol (3 x 10(-6) M), and atropine (10(-6) M) and contracted to 3 x 10(-7) M of the thromboxane analogue U46619, electrical field stimulation (EFS) evoked frequency-dependent relaxations, which were markedly reduced in the presence of tetrodotoxin (10(-6) M). 3. Exogenous NO added as acidified sodium nitrite (10(-6)-10(-3) M) and L-nitrosocysteine induced potent relaxations of lamb coronary small arteries. However, both inhibition of NO synthase with NG- nitro-L-arginine (L-NOARG, 3 x 10(-5) M), and mechanical endothelial cell removal increased rather than inhibited relaxations to EFS. In small arteries processed for NADPH-diaphorase histochemistry, activity was only observed within endothelial cells. 4. In arteries contracted to U46619, exogenously added ATP caused concentration-dependent relaxations with pD2 and maximum responses of 4.72 +/- 0.12 and 89.6 +/- 3.8% (n = 12), respectively. ADP and the P2Y-agonist, 2-methylthio-ATP, induced relaxations equipotent to ATP, while the P2x-agonist, alpha, beta-methylene ATP (10(-9)-10(-4) M), and the P2U-agonist, UTP (10(-9)-10(-4) M) only caused small transient relaxations at the highest concentrations (10(-4) and 10(-3) M). 5. ATP and EFS-induced relaxations were unchanged in the presence of the P1-purinoceptor antagonist, 8-phenyltheophylline (10(-5) M), while this antagonist inhibited the concentration-dependent relaxations to adenosine. In contrast, the P2-purinoceptor antagonist, suramin (3 x 10(-5) M), markedly reduced the relaxations to EFS. 6. After desensitization of P2x-purinoceptors with alpha, beta-methylene ATP (2 x 10(-5) M), the relaxations to exogenous added ATP were enhanced, but this procedure did not influence the relaxations to EFS. In contrast, the P2y-purinoceptor antagonist, basilen blue E-3G (3 x 10(-5) M, earlier named reactive blue 2) significantly inhibited the concentration-relaxation curves to ATP and almost abolished the EFS-induced relaxations. 7. Mechanical removal of the endothelium significantly inhibited ATP-induced maximal relaxations without affecting sensitivity, pD2 and maximum relaxations being 4.72 +/- 0.12 and 89.7 +/- 3.8% (n = 10), and 5.45 +/- 0.38 and 48.0 +/- 8.6% (P < 0.05, paired t test, n = 10) in endothelium-intact and -denuded coronary small arteries, respectively. However, incubation with L-NOARG did not change relaxations elicited by ATP. 8. The present study suggests that in NANC conditions neurogenic relaxations of coronary small arteries are mediated by ATP, which relaxes coronary small arteries through P2Y-purinoceptors. A prejunctional modulation of these relaxations by endothelial-derived NO cannot be excluded.

Effect of parasympathetic and sensory transmitters on human epicardial coronary arteries and veins

Vasomotor effects of various agonists were tested on isolated human epicardial coronary arteries and veins at resting tension and after precontraction with U46619. Acetylcholine relaxed all arteries with intact endothelium but only some endothelium-denuded arteries. Most veins did not relax to acetylcholine. Higher concentrations of acetylcholine induced powerful contractions of all arteries and veins. Preincubation with atropine significantly lowered the pD(2) values but not E(max) values for contractile responses to acetylcholine in arteries and veins (pA(2) value for atropine 9.1 arteries and 9.6 veins). Vasoactive intestinal peptide, human alpha-calcitonin gene-related peptide and substance P potently relaxed all arteries with intact endothelium and all veins. Removal of the arterial endothelium abolished relaxation to substance P in most arteries whereas responses to vasoactive intestinal peptide were unaffected, and for alpha-calcitonin gene-related peptide the pD(2) value but not the E(max) value was significantly lowered. In both arteries and veins, the antagonists alpha-calcitonin gene-related peptide (8-37) and spantide lowered significantly the potency for alpha-calcitonin gene-related peptide and substance P, respectively, without significant changes in E(max) values (pA(2) value for alpha-calcitonin gene-related peptide (8-37) 7.9 arteries and 7.9 veins, for spantide 7.6 arteries and 8.1 veins).