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Unresolved endoplasmic reticulum (ER) stress, with the subsequent persistent activation of the unfolded protein response (UPR) is a well-recognized mechanism of endothelial cell apoptosis with a major impact on the integrity of the endothelium during the course of cardiovascular diseases. As in other cell types, Ca2+ influx into endothelial cells can promote ER stress and/or contribute to mechanisms associated to it. In previous work we showed that in human coronary artery endothelial cells (HCAECs) the Ca2+-permeable non-selective cation channel Transient Receptor Potential Canonical 3 (TRPC3) mediates constitutive Ca2+ influx which is critical for operation of inflammatory signaling in these cells, through a mechanism that entails coupling of TRPC3 constitutive function to activation of Ca2+/calmodulin-dependent protein kinase II (CAMKII). TRPC3 has been linked to UPR signaling and apoptosis in cells other than endothelial, and CAMKII is a mediator of ER stress-induced apoptosis in various cell types, including endothelial cells. In the present work we used a pharmacological approach to examine whether in HCAECs TRPC3 and CAMKII also contribute to mechanisms of ER stress-induced apoptosis. The findings show for the first time that in HCAECs activation of the UPR and the subsequent ER stress-induced apoptosis exhibit a strong requirement for constitutive Ca2+ influx and that TRPC3 contributes to this process. In addition, we obtained evidence indicating that, similar to its roles in non-endothelial cells, CAMKII participates in ER stress-induced apoptosis in HCAECs.

In the cardiovascular and hematopoietic systems the Transient Receptor Potential Canonical 3 (TRPC3) channel has a well-recognized role in a number of signaling mechanisms that impact the function of diverse cells and tissues in physiology and disease. The latter includes, but is not limited to, molecular and cellular mechanisms associated to the pathogenesis of cardiac hypertrophy, hypertension and endothelial dysfunction. Despite several of these functions being closely related to atherorelevant mechanisms, the potential roles of TRPC3 in atherosclerosis, the major cause of coronary artery disease, have remained largely unexplored. Over recent years, a series of studies from the authors' laboratory revealed novel functions of TRPC3 in mechanisms related to endothelial inflammation, monocyte adhesion to endothelium and survival and apoptosis of macrophages. The relevance of these new TRPC3 functions to atherogenesis has recently began to receive validation through studies in mouse models of atherosclerosis with conditional gain or loss of TRPC3 function. This chapter summarizes these novel findings and provides a discussion of their impact in the context of atherosclerosis, in an attempt to delineate a framework for further exploration of this terra incognita in the TRPC field.

Crosstalk between Ca2+ signaling pathways has been demonstrated to facilitate secretory activity. However it is not known whether such a crosstalk exists between adrenergic receptor signaling pathway and a non‐cholinergic non‐adrenergic (NANC) pathway (purinergic pathway). In this study we use enzymatically isolated mouse parotid acini along with live cell Ca2+ imaging and pharmacological manipulations to assess crosstalk between these two pathways.We showed that [Ca2+]i rises induced by selective activation of P2X4R and P2X7R were potentiated three to eightfold following treatment with the cAMP elevating compounds forskolin, 8‐cpt‐cAMP or 3‐isobutyl‐1‐methylxanthine. Importantly, rises in cAMP levels evoked by β‐adrenergic receptor activation using isoprenalin also resulted in a marked enhancement of P2X‐mediated [Ca2+]i signals.Potentiation of P2X4R‐mediated [Ca2+]i signals following β‐adrenergic receptor activation was likely mediated by PKA because protein kinase inhibitor application in the presence of forskolin or isoprenalin abolished the enhancement of evoked [Ca2+]i signals. Interestingly, application of 2‐Aminoethoxydiphenyl borate during P2X7R stimulation also abolished the enhancement of [Ca2+]i rises following isoprenalin treatment.The results from this study reveal a crosstalk between purinergic and β‐adrenergic signaling pathways and may provide novel targets for construction of therapies for salivary hypofunction patients.

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