Effects of protease-activated receptors (PARs) on intracellular calcium dynamics of acinar cells in rat lacrimal glands

Purinergic control of apical ion conductance by luminal ATP in rat colonic epithelium

ATP, released e.g. after cell damage or during inflammation, can alter ion transport across the intestinal mucosa via stimulation of purinergic receptors in the basolateral as well as in the apical membrane of epithelial cells. When ATP acts from the serosal side, it induces an increase in short-circuit current (Isc) via Cl- secretion across the colonic epithelium. In contrast, mucosal ATP or its derivative, BzATP, predominantly stimulating ionotropic P2X4 and P2X7 receptors, evoke an increase in Isc, which could not be explained by Cl- secretion. The underlying ion currents after stimulation of apical purinergic receptors in rat distal colon are still unclear and were investigated in the present study. Ussing chamber experiments revealed that the Isc induced by mucosal ATP was dependent on the presence of mucosal Ca2+ and inhibited by the K+ channel blocker, Ba2+, indicating the involvement of Ca2+-dependent K+ channels. Blockade of the transepithelial Isc by lanthanides (La3+, Gd3+) suggests that Ca2+ enters the epithelium via nonselective cation channels. Experiments with basolaterally depolarized epithelia confirmed the activation of apical lanthanide-sensitive Na+- and Ca2+-permeable cation channels by ATP. Putative candidates might be TRP channels, from which several subtypes were detected in colonic tissue in RT-PCR experiments. In addition, the activation of an apical Cl- conductance was observed when suitable Cl- concentration gradients were applied. Consequently, mucosal ATP, acting as 'danger signal', stimulates cation and anion channels in the apical membrane to induce a secretory response as part of the local defence mechanism in the intestinal epithelium.

Pathophysiological Role and Drug Modulation of Calcium Transport in Ocular Surface Cells

The ocular surface structure and extraocular accessory organs constitute the ocular surface system, which includes the cornea, conjunctiva, eyelids, lacrimal organs, and lacrimal passages. This system is composed of, and stabilized by, the corneal epithelium, conjunctival cells, conjunctival goblet cells, lacrimal acinar cells and Tenon's fibroblasts, all of which maintain the healthy eyeball surface system. Ocular surface diseases are commonly referred to corneal and conjunctival disease and external ocular disease, resulting from damage to the ocular surface structure. A growing body of evidence has indicated that abnormal activation of the KCa3.1 channel and Ca2+/ calmodulin-dependent kinase initiates ocular injury. Signaling pathways downstream of the irregular Ca2+ influx induce cell progression and migration, and impair tight junctions, epithelial transport and secretory function. In this overview, we summarize the current knowledge regarding ocular surface disease in terms of physical and pathological alteration of the ocular system. We dissect in-depth, the mechanisms underlying disease progression, and we describe the current calcium transport therapeutics and the obstacles that remain to be solved. Finally, we summarize how to integrate the research results into clinical practice in the future.

Vorapaxar and diplopia: Possible off-target PAR-receptor mismodulation

Vorapaxar, a novel antiplatelet thrombin PAR-1 inhibitor, has been evaluated in the successful TRA2P trial and the failed TRACER trial. The drug is currently approved for post myocardial infarction and peripheral artery disease indications with concomitant use of clopidogrel and/or aspirin. The FDA ruled that the vorapaxar safety profile is acceptable. However, both trials revealed excess diplopia (double vision) usually reversible after vorapaxar. The diplopia risk appears to be small (about 1 extra case per 1,000 treated subjects), but real. Overall, there were 10 placebo and 34 vorapaxar diplopia cases (p=0.018) consistent for TRACER (2 vs 13 cases; p=0.010) and for TRA2P (8 vs 21 cases; p=0.018). Hence, we review the FDA-confirmed evidence and discuss potential causes and implications of such a surprising adverse association, which may be related to off-target PAR receptor mismodulation in the eye.

α1-Adrenoceptors relate Ca(2+) modulation and protein secretions in rat lacrimal gland

Noradrenaline (NA) is a catecholamine with multiple roles including as a hormone and a neurotransmitter. Cellular secretory activities are enhanced by adrenergic stimuli as well as by cholinergic stimuli. The present study aimed to determine which adrenoceptors play a role in controlling intracellular calcium ion ([Ca(2+)]i) level in acinar cells of rat lacrimal glands. Expression of mRNA for adrenoceptor subtypes in the acinar cells was assessed using RT-PCR. All types except α2c, β1, and β3 were detected. NA induced a [Ca(2+)]i increase with a biphasic pattern in the acinar cells. Removal of extracellular Ca(2+) and use of Ca(2+)-channel blockers did not inhibit the NA-induced [Ca(2+)]i increases. In contrast, U73122 and suramin almost blocked these increases. The α1-adrenoceptor agonist phenylephrine induced a strong increase in [Ca(2+)]i. However, clonidine and isoproterenol failed to induce a [Ca(2+)]i increase. The peroxidase activity was quantified as a measure of mucin secretion. Ca(2+)-dependent exocytotic secretion of peroxidase was detected in rat lacrimal glands. The RT-PCR results showed that MUC1, MUC4, MUC5AC, MUC5B, and MUC16 were expressed in acinar cells. These findings indicated that NA activates α1-adrenoceptors, which were found to be the main receptors in Ca(2+)-related cell homeostasis and protein (including mucin) secretion in lacrimal glands.

The Histochem Cell Biol conspectus: the year 2013 in review

Herein, we provide a brief synopsis of all manuscripts published in Histochem Cell Biol in the year 2013. For ease of reference, we have divided the manuscripts into the following categories: Advances in Methodologies; Molecules in Health and Disease; Organelles, Subcellular Structures and Compartments; Golgi Apparatus; Intermediate Filaments and Cytoskeleton; Connective Tissue and Extracellular Matrix; Autophagy; Stem Cells; Musculoskeletal System; Respiratory and Cardiovascular Systems; Gastrointestinal Tract; Central Nervous System; Peripheral Nervous System; Excretory Glands; Kidney and Urinary Bladder; and Male and Female Reproductive Systems. We hope that the readership will find this annual journal synopsis of value and serve as a quick, categorized reference guide for “state-of-the-art” manuscripts in the areas of histochemistry, immunohistochemistry, and cell biology.

Calcium signaling in lacrimal glands

Lacrimal glands provide the important function of lubricating and protecting the ocular surface. Failure of proper lacrimal gland function results in a number of debilitating dry eye diseases. Lacrimal glands secrete lipids, mucins, proteins, salts and water and these secretions are at least partially regulated by neurotransmitter-mediated cell signaling. The predominant signaling mechanism for lacrimal secretion involves activation of phospholipase C, generation of the Ca(2+)-mobilizing messenger, IP3, and release of Ca(2+) stored in the endoplasmic reticulum. The loss of Ca(2+) from the endoplasmic reticulum then triggers a process known as store-operated Ca(2+) entry, involving a Ca(2+) sensor in the endoplasmic reticulum, STIM1, which activates plasma membrane store-operated channels comprised of Orai subunits. Recent studies with deletions of the channel subunit, Orai1, confirm the important role of SOCE in both fluid and protein secretion in lacrimal glands, both in vivo and in vitro.