Separate agonist-specific oscillatory mechanisms in cultured human sweat duct cells

The family of kallikrein-related peptidases and kinin peptides as modulators of epidermal homeostasis

The epidermis is the outermost skin layer and is part of one of the largest organs in the body; it is supported by the dermis, a network of fibrils, blood vessels, pilosebaceous units, sweat glands, nerves, and cells. The skin as a whole is a protective shield against numerous noxious agents, including microorganisms and chemical and physical factors. These functions rely on the activity of multiple growth factors, peptide hormones, proteases, and specific signaling pathways that are triggered by the activation of distinct types of receptors sited in the cell membranes of the various cell types present in the skin. The human kallikrein family comprises a large group of 15 serine proteases synthesized and secreted by different types of epithelial cells throughout the body, including the skin. At this site, they initiate a proteolytic cascade that generates the active forms of the proteases, some of which regulate skin desquamation, activation of cytokines, and antimicrobial peptides. Kinin peptides are formed by the action of plasma and tissue kallikreins on kininogens, two plasma proteins produced in the liver and other organs. Although kinins are well known for their proinflammatory abilities, in the skin they are also considered important modulators of keratinocyte differentiation. In this review, we summarize the contributions of the kallikreins and kallikrein-related peptidases family and those of kinins and their receptors in skin homeostasis, with special emphasis on their pathophysiological role.

Role of Bradykinin Type 2 Receptors in Human Sweat Secretion: Translational Evidence Does Not Support a Functional Relationship

Bradykinin increases skin blood flow via a cGMP mechanism but its role in sweating in vivo is unclear. There is a current need to translate cell culture and nonhuman paw pad studies into in vivo human preparations to test for therapeutic viability for disorders affecting sweat glands. Protocol 1: physiological sweating was induced in 10 healthy subjects via perfusing warm (46-48°C) water through a tube-lined suit while bradykinin type 2 receptor (B2R) antagonist (HOE-140; 40 μM) and only the vehicle (lactated Ringer's) were perfused intradermally via microdialysis. Heat stress increased sweat rate (HOE-140 = +0.79 ± 0.12 and vehicle = +0.64 ± 0.10 mg/cm2/min), but no differences were noted with B2R antagonism. Protocol 2: pharmacological sweating was induced in 6 healthy subjects via intradermally perfusing pilocarpine (1.67 mg/mL) followed by the same B2R antagonist approach. Pilocarpine increased sweating (HOE-140 = +0.38 ± 0.16 and vehicle = +0.32 ± 0.12 mg/cm2/min); again no differences were observed with B2R antagonism. Last, 5 additional subjects were recruited for various control experiments which identified that a functional dose of HOE-140 was utilized and it was not sudorific during normothermic conditions. These data indicate B2R antagonists do not modulate physiologically or pharmacologically induced eccrine secretion volumes. Thus, B2R agonist/antagonist development as a potential therapeutic target for hypo- and hyperhidrosis appears unwarranted.

Ruled by waves? Intracellular and intercellular calcium signalling

The field of calcium signalling has evolved rapidly the last 20 years. Physiologists had worked with cytosolic Ca2+ as the coupler of excitation and contraction of muscles and as a secretory signal in exocrine glands and in the synapses of the brain for several decades before the discovery of cellular calcium as a second messenger. Development of powerful techniques for measuring the concentration of cytosolic free calcium ions in cell suspensions and later in single cells and even in different cellular compartments, has resulted in an upsurge in the knowledge of the cellular machinery involved in intracellular calcium signalling. However, the focus on intracellular mechanisms might have led this field of study away from physiology. During the last few years there is an increasing evidence for an important role of calcium also as an intercellular signal. Via gap junctions calcium is able to co-ordinate cell populations and even organs like the liver. Here we will give an overview of the general mechanisms of intracellular calcium signalling, and then review the recent data on intercellular calcium signals. A functional coupling of cells in different tissues and organs by the way of calcium might be an important mechanism for controlling and synchronizing physiological responses

Electrophysiological responses to oxytocin and ATP in monolayers of a human sweat gland cell line

It was shown that oxytocin (OT) elicits electrophysiological responses in cultured monolayers of NCL-SG3, a human immortalized sweat gland cell line. The response to OT was greater for basal applications. It was also found that monolayers respond to ATP with a transient transepithelial-potential change, with a more pronounced response to apical than to basal applications. The IC50 for the response to OT was 180 nM at room temperature. The response to OT was not due to effects of OT on vasopressin (AVP) receptors as evidenced by three tests: (a) The response was completely blocked by the selective OT-receptor antagonist [Mpa1,D-Tyr(Et)2,Thr4,Orn8]-OT (CAP) applied at equal concentrations (100-1000 nM) to that of OT. (b) The response to OT was similar to that of ionomycin (2 microM) or ATP (150 microM). In contrast, the response to AVP (500 nM) or cAMP (2 mM) were smaller and of a different time course. (c) OT increased but AVP had no effect on the intracellular free calcium. It is suggested that OT may have a role in the regulation of salt balance in sweating.

Relationship between latency and period for 5-hydroxytryptamine-induced membrane responses in the Calliphora salivary gland

Following stimulation with a calcium-mobilizing agonist there is often a distinct latency (L) preceding the onset of the first calcium spike. In the continued presence of the agonist, repetitive spikes appear separated by a variable period (P). The relationship between L and P has been investigated in an insect salivary gland responding to 5-hydroxytryptamine (5-HT). Both L and P were found to decrease as the concentration of 5-HT was increased over its physiological range of 1-10 nM. Lowering the concentration of external calcium from 1 x 10(-3) M to 1 x 10(-5) M increased both P and L. However, the effect on L was apparent only at low levels of 5-HT. Reducing the content of the internal stores by repeated stimulation in a calcium-free medium resulted in a progressive prolongation of L. On the other hand, the effect of L decreased when glands were stimulated repetitively in normal calcium-containing medium. All these results are consistent with a hypothesis that calcium plays a critical role in determining the kinetics of calcium release during both L and P. An important component seems to be the entry of external calcium, which sets the stage for calcium release by loading up the internal stores. As these stores fill up with calcium, the Ins(1,4,5)P3 receptors will initiate a calcium spike once they become sensitized to the ambient level of Ins(1,4,5)P3.

Spatial and temporal signalling by calcium

Recent research has shown the importance of the spatial and temporal aspects of calcium signals, which depend upon regenerative properties of the inositol trisphosphate and ryanodine receptors that regulate the release of calcium from internal stores. Initiation sites have been found to spontaneously release calcium, recognized as 'hot spots' or 'sparks', and can trigger a wave that spreads through a process of calcium-induced calcium release.

Inositol triphosphate produces different patterns of cytoplasmic Ca2+ spiking depending on its concentration

In single mouse pancreatic acinar cells the effects of intracellular infusion of inositol 1,4,5-trisphosphate (InsP3) or the non-metabolizable InsP3 analogue inositol 1,4,5-triphosphorothioate (InsPS3) have been investigated using a wide range of concentrations. Different types of cytosolic Ca2+ fluctuation patterns (monitored as Ca(2+)-dependent Cl- current in patch-clamp whole-cell recording experiments) could be generated by InsP3 or InsPS3, dependent on concentration, resembling those previously shown to be evoked by varying degrees of receptor activation in these cells. Low InsPS3 concentrations evoked repetitive local Ca2+ spikes whereas at relatively high concentrations repetitive Ca2+ waves were produced. In the presence of intracellular citrate a much lower messenger level was sufficient to generate waves. The InsP3 concentration determines whether the cytosolic Ca2+ signals are local or global.

Calcium regulation and homeostasis

The use of techniques to visualize the stimulus-induced changes in [Ca2+]i that occur at the single cell level has revealed that intracellular Ca2+ signals can be remarkably organized in space (waves), as well as in time (oscillations). New insights are beginning to emerge into how these complex Ca2+ signals may be generated, and into how Ca2+ signals may be transmitted from cell to cell.