Mast cells play a key role in modulation of stress-induced cutaneous inflammation. In this study we investigate the impact of repeated exposure to stress on mast cell degranulation, in both hairy and glabrous skin. Adult male Wistar rats were randomly divided into four groups: Stress 1 day (n = 8), Stress 10 days (n = 7), Stress 21 days (n = 6), and Control (n = 8). Rats in the stress groups were subjected to 2 h/day restraint stress. Subsequently, glabrous and hairy skin samples from animals of all groups were collected to assess mast cell degranulation by histochemistry and transmission electron microscopy. The impact of stress on mast cell degranulation was different depending on the type of skin and duration of stress exposure. Short-term stress exposure induced an amplification of mast cell degranulation in hairy skin that was maintained after prolonged exposure to stress. In glabrous skin, even though acute stress exposure had a profound stimulating effect on mast cell degranulation, it diminished progressively with long-term exposure to stress. The results of our study reinforce the view that mast cells are active players in modulating skin responses to stress and contribute to further understanding of pathophysiological mechanisms involved in stress-induced initiation or exacerbation of cutaneous inflammatory processes.

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1 Adenosine 5 0 -triphosphate (ATP) is known to augment cardiac contractile activity and cause an increase in intracellular Ca 2 þ concentration ([Ca 2 þ ] i ) in isolated cardiomyocytes. However, no information regarding the ATP-mediated signal transduction in the myocardium in congestive heart failure (CHF) is available. 2 CHF due to myocardial infarction (MI) in rats was induced by the occlusion of the left coronary artery for 8 weeks. The positive inotropy due to ATP was depressed in failing hearts. Treatment of 3 weeks infarcted animals with imidapril (1 mg kg À1 day À1 ) for a period of 5 weeks improved the left ventricle function and decreased the attenuation of inotropic response to ATP. 3 ATP-induced increase in [Ca 2 þ ] i was significantly depressed in cardiomyocytes isolated from the failing heart and this change was partially attenuated by imidapril treatment. However, the binding characteristics of 35 S-labeled adenosine 5 0 -(g-thio) triphosphate in sarcolemma isolated from the failing heart remained unaltered. 4 ATP-induced increase in [Ca 2 þ ] i was depressed by verapamil and cibacron blue in both control and failing heart cardiomyocytes; however, the ATP response in the failing hearts, unlike the control preparations, was not decreased by ryanodine. This insensitivity to ryanodine was attenuated by imidapril treatment. 5 Treatment of infarcted rats with enalapril and losartan produced effects similar to imidapril. 6 These findings indicate that the positive inotropic response to ATP and ATP-induced increase in [Ca 2 þ ] i in cardiomyocytes are impaired in heart failure. Furthermore, blockade of renin angiotensin system prevented the impairment of the ATP-mediated inotropic and [Ca 2 þ ] i responses in the failing heart.

We previously demonstrated that cardiac sarcolemmal membranes bind [35S]ATP gamma S at both low and high affinity binding sites. In this study we examined the effects of some P2-purinoceptor antagonists as well as of two oxidants (H2O2 and HOCl) on the high affinity ATP-binding sites under in vitro conditions. It was found that putative P2-purinoceptor antagonists such as Cibacron blue, suramin, and 4,4'-diisothiocyanatostilbene 2-2 acid markedly inhibited specific ATP-binding with sarcolemmal membrane. H2O2 produced a biphasic effect (first increase and then decrease) on the specific ATP-binding with cardiac sarcolemma in a time- and concentration-dependent manner; these effects were prevented by catalase. On the other hand, HOCl markedly inhibited ATP-binding; this inhibition was prevented by l-methionine. These results suggest that the high affinity ATP-binding sites in cardiac sarcolemma may represent the P2-purinoceptors, which are susceptible to modification by oxidative stress under pathophysiological conditions including myocardial ischemia-reperfusion injury.

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BACKGROUND: It is generally accepted that the plasma membrane of mammalian ventricular myocytes regulates the cytosolic concentration of Ca(2+). In this study we investigated the effects of some P2-purinoceptor antagonists and metals such as copper and zinc on the adenosine triphosphate (ATP)-induced increase in intracellular concentration of free Ca(2+) ([Ca(2+)](i)). METHODS AND RESULTS: Cardiomyocytes were isolated from adult male Sprague-Dawley rats loaded with Fura-2, and fluorescence measurements were performed by employing stirred cell suspensions at room temperature. ATP (50 µM) increased [Ca(2+)](i) over the basal value, and 10 µM cibacron blue or verapamil virtually abolished it. The ATP-induced increase in [Ca(2+)](i) was not observed in Ca(2+)- or Mg(2+)-free buffers. Incubation of cells with ZnCl(2) produced a significant depression of the ATP-induced increase in [Ca(2+)](i); 25 µM Zn(2+) decreased the peak response to approximately 50% of the control value. The ATP-induced increase in [Ca(2+)](i), was inhibited by low concentrations (1-5 µM) of Cu(2+) but was markedly augmented by high concentrations (25 µM) of Cu(2+). The increase in the [Ca(2+)](i) response to cron blue, and Zn(2+), but not by ryanodine or caffeine pretreatment. CONCLUSIONS: The ATP-induced increase in [Ca(2+)](i) is dependent on the extracellular concentrations of Ca(2+) as well as Mg(2+) and is antagonized by cibacron blue and Zn(2+). On the other hand, Cu(2+) produced a biphasic response to the ATP-induced increase in [Ca(2+)](i) in cardiomyocytes.

Although vitamin B6 deficiency is related to coronary heart disease, no information regarding changes in myocardium due to vitamin B6 deficiency is available in the literature. In view of the critical role played by Ca2+ in cellular function, we investigated alterations in [Ca2+]i induced by KCI or ATP in vitamin B6 deficient and age-matched control rats. [Ca2+]i was measured in isolated cardiomyocytes by using the Fura-2 fluorescence technique. The KC1-induced increase in [Ca2+]i was augmented in vitamin B6 deficient cardiomyocytes, whereas the ATP-induced increase in [Ca2+]i was attenuated. The specific ATP binding to sarcolemma from hearts of vitamin B6 deficient rats was decreased. A single injection of vitamin B6 (10 mg/kg) to vitamin B6 deficient animals completely reversed the KC1- or ATP-induced changes in [Ca2+]i in cardiomyocytes as well as ATP binding with sarcolemma. These results regarding altered regulation of [Ca2+]i in cardiomyocytes and sarcolemmal ATP receptors indicate myocardial abnormalities due to vitamin B6 deficiency.

Channelopathies represent diseases caused by mutations in the genes encoding ion channels or associated proteins. With the advent of novel electrophysiology and molecular biology techniques, a wide variety of ion channels have been identifi ed in different regions of the working myocardium or conduction system, and their biophysical and pharmacological properties, as well as involvement in different pathophysiology processes, are thoroughly characterized. This wealth of knowledge offers a better understanding of the intricate chemical and electrical events underlying a large class of rare heart diseases, most of them associated with arrhythmias, and also reveals novel mechanisms in the most frequent cardiovascular diseases and their complications. Within the present chapter we tackled the challenging task of presenting a comprehensive review of this rapidly expanding domain, with the hope of rendering relevant information for specialists with an interest in this highly exciting fi eld of research.