A major pathway for stimulated Ca²⁺ entry in non-excitable cells is activated following depletion of intracellular Ca²⁺ stores. Secretion-like coupling between elements in the plasma membrane (PM) and Ca²⁺ stores has been proposed as the most likely mechanism to activate this store-mediated Ca²⁺ entry (SMCE) in several cell types. Here we identify two mechanisms for SMCE in human platelets activated by depletion of two independent Ca²⁺ pools, which are differentially modulated by the actin cytoskeleton. Ca²⁺ entry induced by depletion of a 2,5-di-(tert-butyl)-1,4-hydroquinone (TBHQ)-sensitive pool is increased by disassembly of the actin cytoskeleton and that induced by a TBHQ-insensitive pool is reduced. Stabilization of the actin cytoskeleton prevented Ca²⁺ entry by both mechanisms. We propose that the membrane-associated actin network prevents constitutive Ca²⁺ entry via both pathways. Reorganization of the actin cytoskeleton permits the activation of Ca²⁺ entry via both mechanisms, but only SMCE activated by the TBHQ-insensitive pool requires new actin polymerization, which may support membrane trafficking toward the PM.

Summary. Background: Platelets play a role in a number of inflammatory conditions including atherosclerosis; however, the mechanisms of platelet activation under these conditions are unclear. Objectives: To investigate the presence of the vanilloid receptor, TRPV1, which is stimulated by noxious stimuli and by inflammatory mediators, in human platelets. Methods: Platelets loaded with fura‐2 or sodium‐binding benzofuran isophalate acetoxymethyl ester (SBFI) were used to monitor cytosolic calcium or sodium concentrations. 5‐HT secretion was determined by fluorescence assay after conjugation with o‐phthaldialdehyde. ATP secretion was determined using luciferin‐luciferase. Results: TRPV1 was identified by Western blotting using a specific anti‐hTRPV1 antibody. The TRPV1 agonist, capsaicin, evoked both Ca²⁺ influx and Ca²⁺ release from intracellular stores, responses that were blocked in a dose‐dependent manner by the TRPV1 antagonists, 5′‐Iodo‐resiniferatoxin (5′‐Iodo‐RTX) and AMG 9810. Capsaicin also increased platelet cytosolic [Na⁺]. Capsaicin‐evoked Ca²⁺ release was abolished in the absence of extracellular Na⁺ or by the 5‐HT_2A receptor antagonist, ketanserin. Capsaicin evoked 5‐HT release from platelets, a response abolished in the absence of extracellular Na⁺ or by 5′‐Iodo‐RTX. Thus capsaicin‐evoked Ca²⁺ release appeared to be mediated by Na⁺‐dependent 5‐HT release. TRPV1‐dependent 5‐HT release also contributed to ADP‐ and thrombin‐evoked Ca²⁺ entry and release. 5′‐Iodo‐RTX reduced ADP‐ and thrombin‐evoked Ca²⁺ signals, effects not additive with those of ketanserin, and 5′‐Iodo‐RTX inhibited agonist‐evoked 5‐HT and ATP release. Conclusion: These results indicate that TRPV1 is present and functionally important in human platelets. The presence of this receptor may provide a link between inflammatory mediators and platelet activation in conditions such as atherosclerosis.

Cystic fibrosis-related diabetes (CFRD) is the most significant extra-pulmonary comorbidity in cystic fibrosis (CF) patients, and accelerates lung decline. In addition to the traditional view that CFRD is a consequence of fibrotic destruction of the pancreas as a whole, emerging evidence may implicate a role for cystic fibrosis transmembrane-conductance regulator (CFTR) in the regulation of insulin secretion from the pancreatic islet. Impaired first-phase insulin responses and glucose homeostasis have also been reported in CF patients. CFTR expression in both human and mouse beta cells has been confirmed, and recent studies have shown differences in endocrine pancreatic morphology from birth in CF. Recent experimental evidence suggests that functional CFTR channels are required for insulin exocytosis and the regulation of membrane potential in the pancreatic beta cell, which may account for the impairments in insulin secretion observed in many CF patients. These novel insights suggest that the pathogenesis of CFRD is more complicated than originally thought, with implications for diabetes treatment and screening in the CF population. This review summarises recent emerging evidence in support of a primary role for endocrine pancreatic dysfunction in the development of CFRD. Summary • CF is an autosomal recessive disorder caused by mutations in the CFTR gene • The vast majority of morbidity and mortality in CF results from lung disease. However CFRD is the largest extra-pulmonary co-morbidity and rapidly accelerates lung decline • Recent experimental evidence shows that functional CFTR channels are required for normal patterns of first phase insulin secretion from the pancreatic beta cell • Current clinical recommendations suggest that insulin is more effective than oral glucose-lowering drugs for the treatment of CFRD. However, the emergence of CFTR corrector and potentiator drugs may offer a personalised approach to treating diabetes in the CF population