Immunohistochemical localization of P2Y12 purinoceptors in the rat carotid body

The present study investigated the localization of the adenosine 5'-diphosphate (ADP)-selective P2Y12 purinoceptors in the rat carotid body using multilabeling immunofluorescence. Punctate immunoreactive products for P2Y12 were distributed in chemoreceptive type I cells immunoreactive to vesicular nucleotide transporter (VNUT) or dopamine beta-hydroxylase, but not in S100B-immunoreactive glial-like type II cells. P2Y12 immunoreactivity was localized in cell clusters containing VNUT-immunoreactive type I cells surrounded by the perinuclear cytoplasm and cytoplasmic processes of type II cells immunoreactive for ectonucleoside triphosphate diphosphohydrolase 2 (NTPDase2) and NTPDase3, which hydrolyze extracellular nucleotide tri- and/or di-phosphates. In ATP bioluminescence assays using carotid bodies, the degradation of extracellular ATP was attenuated in the presence of the selective NTPDases inhibitor ARL67156, suggesting ATP-degrading activity by NTPDases in the tissue. These results suggest that ATP released from type I cells is degraded into ADP and adenosine 5'-monophosphate by NTPDases expressed in type II cells, and that ADP modulates type I cells via P2Y12 purinoceptors.

A convenient fluorimetry-based degranulation assay using RBL-2H3 cells

Type I hypersensitivity is triggered by mast cell degranulation, a stimulus-induced exocytosis of preformed secretory granules (SGs) containing various inflammatory mediators. The degree of degranulation is generally expressed as a percentage of secretory granule markers (such as β-hexosaminidase and histamine) released into the external solution, and considerable time and labor are required for the quantification of markers in both the supernatants and cell lysates. In this study, we developed a simple fluorimetry-based degranulation assay using rat basophilic leukemia (RBL-2H3) mast cells. During degranulation, the styryl dye FM1-43 in the external solution fluorescently labeled the newly exocytosed SGs, whose increase in intensity was successively measured using a fluorescence microplate reader. In addition to the rate of β-hexosaminidase secretion, the cellular FM1-43 intensity successfully represented the degree and kinetics of degranulation under various conditions, suggesting that this method facilitates multi-sample and/or multi-time-point analyses required for screening substances regulating mast cell degranulation.

ADP-mediated Modulation of Intracellular Calcium Responses in Chromaffin Cells: The Role of Ectonucleoside Triphosphate Diphosphohydrolase 2 on Rat Adrenal Medulla Function

The present study investigated the localization and the adenosine 5'-triphosphate (ATP)-degrading function of the plasma membrane-bound ecto-nucleotidase, ectonucleoside triphosphate diphosphohydrolase 2 (NTPDase2), in the rat adrenal medulla. The effect of ATP degradation product, adenosine 5'-diphosphate (ADP), on carbachol (CCh)-induced intracellular Ca2+ ([Ca2+]i) responses in adrenal chromaffin cells was examined using calcium imaging. NTPDase2-immunoreactive cells were distributed between chromaffin cells. NTPDase2-immunoreactive cells were immunoreactive for glial fibrillary acidic protein and S100B, suggesting that they were sustentacular cells. NTPDase2-immunoreactive cells surrounded chromaffin cells immunoreactive for vesicular nucleotide transporter and P2Y12 ADP-selective purinoceptors. In ATP bioluminescence assays using adrenal medullary slices, ATP was rapidly degraded and its degradation was attenuated by the NTPDase inhibitors sodium polyoxotungstate (POM-1) and 6-N, N-diethyl-d-β,γ-dibromomethylene ATP (ARL67156). ADP inhibited CCh-induced [Ca2+]i increases of chromaffin cells in adrenal medullary slices. The inhibition of CCh-induced [Ca2+]i increases by ADP was blocked by the P2Y12 purinoceptor antagonist AZD1283. CCh-induced [Ca2+]i increases were also inhibited by the P2Y1, P2Y12, and P2Y13 purinoceptor agonist 2-methylthioadenosine diphosphate trisodium (2MeSADP), in combination with the P2Y1 purinoceptor antagonist MRS2179. These results suggest that sustentacular cells express NTPDase2 to degrade ATP released from adrenal chromaffin cells, and ADP modulates the excitability of chromaffin cells via P2Y12 purinoceptors to regulate catecholamine release during preganglionic sympathetic stimuli. (J Histochem Cytochem 72: 41-60, 2024).

Distribution of P2X3 purinoceptor-immunoreactive sensory nerve endings in the carotid body of Japanese macaque (Macaca fuscata)

In the carotid body of laboratory rodents, adenosine 5'-triphosphate (ATP)-mediated transmission is regarded as critical for transmission from chemoreceptor type I cells to P2X3 purinoceptor-expressing sensory nerve endings. The present study investigated the distribution of P2X3-immunoreactive sensory nerve endings in the carotid body of the adult male Japanese monkey (Macaca fuscata) using multilabeling immunofluorescence. Immunoreactivity for P2X3 was detected in nerve endings associated with chemoreceptor type I cells immunoreactive for synaptophysin. Spherical or flattened terminal parts of P2X3-immunoreactive nerve endings were in close apposition to the perinuclear cytoplasm of synaptophysin-immunoreactive type I cells. Immunoreactivity for ectonucleoside triphosphate diphosphohydrolase 2 (NTPDase2), which hydrolyzes extracellular ATP, was localized in the cell body and cytoplasmic processes of S100B-immunoreactive cells. NTPDase2-immunoreactive cells surrounded P2X3-immunoreactive terminal parts and synaptophysin-immunoreactive type I cells, but did not intrude into attachment surfaces between terminal parts and type I cells. These results suggest ATP-mediated transmission between type I cells and sensory nerve endings in the carotid body of the Japanese monkey, as well as those of rodents.

Suitability of Polymyxin B as a Mucosal Adjuvant for Intranasal Influenza and COVID-19 Vaccines

Polymyxin B (PMB) is an antibiotic that exhibits mucosal adjuvanticity for ovalbumin (OVA), which enhances the immune response in the mucosal compartments of mice. Frequent breakthrough infections of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants indicate that the IgA antibody levels elicited by the mRNA vaccines in the mucosal tissues were insufficient for the prophylaxis of this infection. It remains unknown whether PMB exhibits mucosal adjuvanticity for antigens other than OVA. This study investigated the adjuvanticity of PMB for the virus proteins, hemagglutinin (HA) of influenza A virus, and the S1 subunit and S protein of SARS-CoV-2. BALB/c mice immunized either intranasally or subcutaneously with these antigens alone or in combination with PMB were examined, and the antigen-specific antibodies were quantified. PMB substantially increased the production of antigen-specific IgA antibodies in mucosal secretions and IgG antibodies in plasma, indicating its adjuvanticity for both HA and S proteins. This study also revealed that the PMB-virus antigen complex diameter is crucial for the induction of mucosal immunity. No detrimental effects were observed on the nasal mucosa or olfactory bulb. These findings highlight the potential of PMB as a safe candidate for intranasal vaccination to induce mucosal IgA antibodies for prophylaxis against mucosally transmitted infections.

Immunohistochemical analysis of glutamatergic and serotonergic signaling pathways in chemosensory cell clusters in the pharynx and larynx of rats

The present study examined cellular components and the localization of vesicular glutamate transporter (VGLUT) 1 and 2 and serotonin (5-HT) in chemosensory cell clusters in the rat pharynx and larynx. Triple immunolabeling for guanine nucleotide-binding protein G (t), subunit ⍺3 (GNAT3) and nucleoside triphosphate diphosphohydrolase 2 (NTPDase2) with synaptotagmin-1 (Syt1) revealed NTPDase2-immunoreactive type I-like cells in addition to GNAT3-immunoreactive type II-like and Syt1-immunoreactive type III-like cells in pharyngolaryngeal chemosensory cell clusters. Therefore, these clusters appear to comprise similar cell types to those in the lingual taste buds with slight morphological modifications. An immunofluorescence analysis of VGLUT1 or VGLUT2 and GNAT3 with P2X3 purinoceptors revealed that VGLUTs co-localized to P2X3-immunoreactive spherical nerve terminals closely associated with GNAT3-immunoreactive type II-like cells. Moreover, triple immunolabeling for Syt1/synaptosomal-associated protein, 25 kDa (SNAP25) and P2X3 with VGLUT1 or VGLUT2 revealed punctate immunoreactive products for VGLUT1 and VGLUT2 within P2X3-immunoreactive flat axon terminals wrapped around Syt1/SNAP25-immunoreactive type III-like cells. The afferent nerve fibers innervating cell clusters may contain glutamate and release it by exocytosis. On the other hand, immunoreactive products for 5-HT and dopa decarboxylase were detected in Syt1-immunoreactive cells, indicating the release of 5-HT by these cells. The present results suggest that chemosensory cell clusters in the pharynx and larynx may be modulated by intrinsic glutamate and 5-HT.

Immunolocalization of vesicular glutamate transporter 2 and exocytosis-related proteins in afferent nerve endings innervating taste buds in the rat incisive papilla

The present study aimed to investigate the immunolocalization of vesicular glutamate transporter (VGLUT) 1 and 2, and proteins associated with exocytosis, i.e., core components of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex (synaptosomal-associated protein of 25 kDa, syntaxin 1, and vesicle-associated membrane protein 2) and synaptotagmin-1 (Syt1), in incisive papillary taste buds of rats using double-indirect immunofluorescence. No VGLUT1 immunoreactivity was observed, whereas VGLUT2-immunoreactive punctate products were closely associated with guanine nucleotide-binding protein G(t) subunit α3-immmunoreactive cells in taste buds. VGLUT2 was immunolocalized in P2X3 purinoceptor-expressing afferent nerve endings. Synaptosomal-associated protein of 25 kDa, syntaxin 1, and vesicle-associated membrane protein 2 were immunolocalized in nerve endings containing VGLUT2-immunoreactive products as well as a few cells in taste buds. VGLUT2 was co-immunolocalized in some intragemmal nerve endings immunoreactive for Syt1, a calcium sensor implicated in vesicle membrane fusion. The present results suggest that afferent nerve endings innervating incisive taste buds release glutamate by exocytosis to modulate taste cell function.

3-Iodothyronamine, a trace amine-associated receptor agonist, regulates intracellular Ca2+ increases via CaMK II through Epac2 in rat cerebral arterioles

Trace amines (TAs) in the nervous system bind to TA-associated receptors (TAARs) and are involved in the regulation of monoaminergic functions. Among TAAR subtypes, TAAR1 has been implicated in the development of neurological disorders, such as schizophrenia. The present study investigated the effects of the TAAR1 agonist, 3-iodothyronamine (T1AM) on cerebral arterioles using fluctuations in the intracellular concentration of Ca2+ ([Ca2+]i) as an index of contractile responses. In cerebral arterioles, most of the TAAR agonists did not increase [Ca2+]i, while only T1AM elevated [Ca2+]i in vascular smooth muscle cells. This increase involved extracellular Ca2+ influx through T-type Ca2+ channels and inositol trisphosphate- and ryanodine-receptor-mediated Ca2+ release from intracellular stores. The inhibition of the cAMP sensor, exchange protein directly activated by cAMP (Epac) 2, and calmodulin kinase (CaMK) II strongly inhibited Ca2+ elevations. The present study revealed that T1AM acted not only on the TAAR1 receptor as previously suggested, but also on other G-protein coupled receptors and/or signal transduction systems to increase intracellular Ca2+ in cerebral arteriole smooth muscle cells. These results suggest that when using T1AM in clinical practice, attention should be paid to the early rise in blood pressure.

Morphology and chemical characteristics of taste buds associated with P2X3-immunoreactive afferent nerve endings in the rat incisive papilla

The present study investigated the cellular components and afferent innervations of taste buds in the rat incisive papilla by immunohistochemistry using confocal scanning laser microscopy. Taste buds containing guanine nucleotide-binding protein G(t), subunit α3 (GNAT3)-imunoreactive cells were densely distributed in the lateral wall of incisive papilla forming the opening of nasoincisor ducts. GNAT3-immunoreactive cells in the taste buds were slender in shape and the tips of apical processes gathered at one point at the surface of the epithelium. The number of taste buds was 56.8 ± 4.5 in the incisive papilla. The incisive taste buds also contained ectonucleoside triphosphate diphosphohydrolase 2-immunoreactive cells and synaptotagmin-1-immunoreactive cells in addition to GNAT3-immunoreactive cells. Furthermore, GNAT3-immunoreactive cells were immunoreactive to taste transduction molecules such as phospholipase C, β2-subunit, and inositol 1,4,5-trisphosphate receptor, type 3. P2X3-immunoreactive subepithelial nerve fibers intruded into the taste buds and terminated with hederiform or calix-like nerve endings attached to GNAT3-immunoreactive cells and synaptosomal-associated protein, 25 kDa-immunoreactive cells. Some P2X3-immunoreactive endings were also weakly immunoreactive for P2X2. Furthermore, a retrograde tracing method using fast blue dye indicated that most of the P2X3-immunoreactive nerve endings originated from the geniculate ganglia (GG) of the facial nerve. These results suggest that incisive taste buds are morphologically and cellularly homologous to lingual taste buds and are innervated by P2X3-immunoreactive nerve endings derived from the GG. The incisive papilla may be the palatal taste papilla that transmits chemosensory information in the oral cavity to the GG via P2X3-immunoreactive afferent nerve endings.

Morphology of P2X3-immunoreactive basket-like afferent nerve endings surrounding serosal ganglia and close relationship with vesicular nucleotide transporter-immunoreactive nerve fibers in the rat gastric antrum

We previously reported P2X3 purinoceptor (P2X3)-expressing vagal afferent nerve endings with large web-like structures in the subserosal tissue of the antral lesser curvature, suggesting that these nerve endings were one of the vagal mechanoreceptors. The present study investigated the morphological relationship between P2X3-immunoreactive nerve endings and serosal ganglia in the rat gastric antrum by immunohistochemistry of whole-mount preparations using confocal scanning laser microscopy. P2X3-immunoreactive basket-like subserosal nerve endings with new morphology were distributed laterally to the gastric sling muscles in the distal antrum of the lesser curvature. Parent axons ramified into numerous nerve fibers with pleomorphic flattened structures to form basket-like nerve endings, and the parent axons were originated from large net-like structures of vagal afferent nerve endings. Basket-like nerve endings wrapped around the whole serosal ganglia, which were characterized by neurofilament 200 kDa-immunoreactive neurons with or without neuronal nitric oxide synthase immunoreactivity and S100B-immunoreactive glial cells. Furthermore, basket-like nerve endings were localized in close apposition to dopamine beta-hydroxylase-immunoreactive sympathetic nerve fibers immunoreactive for vesicular nucleotide transporter. These results suggest that P2X3-immunoreactive basket-like nerve endings associated with serosal ganglia are the specialized ending structures of vagal subserosal mechanoreceptors in order to increase the sensitivity during antral peristalsis, and are activated by ATP from sympathetic nerve fibers and/or serosal ganglia for the regulation of mechanoreceptor function.

GluN2A- and GluN2B-immunoreactive type I cells attached to vesicular glutamate transporter 2-immunoreactive afferent nerve terminals of the rat carotid body

We previously reported the immunoreactivity for the vesicular glutamate transporter 2 (VGLUT2) in afferent nerve terminals attached to chemoreceptor type I cells of the carotid body (CB), suggesting that glutamate is released from afferent terminals to stimulate these cells. In the present study, we examined the immunoreactivity for the glutamate-binding subunits of N-methyl-D-aspartate (NMDA) receptors, GluN2A and GluN2B in the rat CB, and the immunohistochemical relationships between these subunits and VGLUT2. Immunoreactivities for GluN2A and GluN2B were predominant in a subpopulation of tyrosine hydroxylase-immunoreactive type I cells rather than those of dopamine beta-hydroxylase-immunoreactive cells. Punctate VGLUT2-immunoreactive products were attached to GluN2A- and GluN2B-immunoreactive type I cells. Bassoon-immunoreactive products were localized between VGLUT2-immunoreactive puncta and type I cells immunoreactive for GluN2A and GluN2B. These results suggest that afferent nerve terminals release glutamate by exocytosis to modulate chemosensory activity of a subpopulation of type I cells via GluN2A- and GluN2B subunits-containing NMDA receptors.

Distribution and morphology of P2X3-immunoreactive subserosal afferent nerve endings in the rat gastric antrum

The present study investigated the morphological characteristics of subserosal afferent nerve endings with immunoreactivity for the P2X3 purinoceptor (P2X3) in the rat stomach by immunohistochemistry of whole-mount preparations using confocal scanning laser microscopy. P2X3 immunoreactivity was observed in subserosal nerve endings proximal and lateral to the gastric sling muscles in the distal antrum of the lesser curvature. Parent axons ramified into several lamellar processes to form net-like complex structures that extended two-dimensionally in every direction on the surface of the longitudinal smooth muscle layer. The axon terminals in the periphery of P2X3-immunoreactive net-like structures were flat and looped or leaf-like in shape. Some net-like lamellar structures and their axon terminals with P2X3 immunoreactivity were also immunoreactive for P2X2. P2X3-immunoreactive nerve fibers forming net-like terminal structures were closely surrounded by S100B-immunoreactive terminal Schwann cells, whereas axon terminals twined around these cells and extended club-, knob-, or thread-like protrusions in the surrounding tissues. Furthermore, a retrograde tracing method using fast blue dye indicated that most of these nerve endings originated from the nodose ganglia of the vagus nerve. These results suggest that P2X3-immunoreactive subserosal nerve endings have morphological characteristics of mechanoreceptors and contribute to sensation of a mechanical deformation of the distal antral wall associated with antral peristalsis.

Morphological characterization of brush cells in the rat trachea

Brush cells have recently been classified as solitary chemosensory cells. However, tracheal brush cells have not been morphologically and immunohistochemically characterized yet. In the present study, the morphological and immunohistochemical characteristics of tracheal brush cells were analyzed using immunohistochemistry and scanning, and transmission electron microscopies. Brush cells in the tracheal epithelium were barrel-like or columnar in shape and were immunoreactive for villin. Scanning and transmission electron microscopies revealed densely arranged thick microvilli on the apical surface of tracheal brush cells and tubular membranous elements and/or vesicular formations in the supranuclear region. A morphometrical analysis of tracheal whole-mount preparations showed that the density of brush cells was greater in the cranial third and the mucosa on the annular ligament. Double immunofluorescence revealed that the morphology of villin-immunoreactive brush cells was distinct from other non-ciliated cells in the tracheal epithelium, i.e., MUC5AC-immunoreactive mucous cells, SNAP25-immunoreactive neuroendocrine cells, and GNAT3-immunoreactive solitary chemosensory cells. On the other hand, tracheal brush cells were immunoreactive for the marker proteins for intestinal brush cells, CK18, DCLK1, and Cox1; however, these antibodies also recognized cells other than brush cells. Furthermore, immunoreactivity for PKD2L1, a cation channel subunit, was detected in brush cells. The present results demonstrated that tracheal brush cells are independent cell types. These brush cells may be activated by acid and the secretion of prostaglandins. In conclusion, the present study revealed that tracheal brush cells are independent cell types based on the morphological and immunohistochemical characteristics.

Vesicular nucleotide transporter-immunoreactive type I cells associated with P2X3-immunoreactive nerve endings in the rat carotid body

ATP is the major excitatory transmitter from chemoreceptor type I cells to sensory nerve endings in the carotid body, and has been suggested to be released by exocytosis from these cells. We investigated the mRNA expression and immunohistochemical localization of vesicular nucleotide transporter (VNUT) in the rat carotid body. RT-PCR detected mRNA expression of VNUT in extracts of the tissue. Immunoreactivity for VNUT was localized in a part of type I cells immunoreactive for synaptophysin (SYN), but not in glial-like type II cells immunoreactive for S100 and S100B. Among SYN-immunoreactive type I cells, VNUT immunoreactivity was selectively localized in the sub-population of tyrosine hydroxylase (TH)-immunorective type I cells associated with nerve endings immunoreactive for the P2X3 purinoceptor; however, it was not detected in the sub-population of type I cells immunoreactive for dopamine beta-hydroxylase. Multi-immunolabeling for VNUT, P2X3, and Bassoon revealed that Bassoon-immunoreactive products were localized in type I cells with VNUT immunoreactivity, and accumulated on the contact side of P2X3-immunoreactive nerve endings. These results revealed the selective localization of VNUT in the subpopulation of TH-immunoreactive type I cells attached to sensory nerve endings and suggested that these cells release ATP by exocytosis for chemosensory transmission in the carotid body.

Different immunohistochemical localization for TMEM16A and CFTR in acinar and ductal cells of rat major salivary glands and exocrine pancreas

We investigated the mRNA expression and immunohistochemical localization of Cl^- channels, transmembrane member 16A (TMEM16A or anoctamin 1), and cystic fibrosis transmembrane conductance regulator (CFTR) in rat major salivary glands and exocrine pancreas. RT-PCR detected mRNA expression of TMEM16A and CFTR in the extracts of the parotid gland (PG), submandibular gland (SMG), sublingual gland (SLG), and pancreas. Immunoreactivity for TMEM16A was localized in the apical membrane of serous acinar and intercalated ductal cells in the PG and SMG as well as mucous acinar cells in the SLG; however, it was not detected in striated ductal cells of these tissues. Although striated ductal cells in the PG, SMG and SLG, and granular ductal cells in the SMG, were immunoreactive for CFTR in the luminal side, serous, mucous acinar, and intercalated ductal cells were not immunoreactive for CFTR in any of the major salivary glands. In the exocrine pancreas, immunoreactivity for TMEM16A was localized in the apical membrane of acinar cells, while immunoreactivity for CFTR was localized in the luminal side of intercalated ductal cells. These results suggest that different localization of TMEM16A and CFTR immunoreactivities reflects the respective functions of acinar and ductal cells in major salivary glands and exocrine pancreas.

Inhibitory role of Munc13-1 in antigen-induced mast cell degranulation

Secretory granules (SGs) of mast cells are lysosome-related organelles that contain various inflammatory molecules such as histamine, which are stored in the cytoplasm. Mast cell degranulation is the regulated exocytosis of SGs in response to external stimuli, such as the antigen-mediated cross-linking of the high-affinity IgE receptor, FcεRI. Upon stimulation, SGs undergo priming to become fusion-competent prior to fusing with the plasma membrane, which is mediated by Munc13-4, one of the five members of the vesicle-priming Munc13 protein family. Although Munc13-4 is shown to be crucial for mast cell degranulation, the functional involvement of other Munc13 isoform(s) remains unknown. Herein, this was investigated using the RBL-2H3 mast cell line. We found that Munc13-1 and Munc13-4 are the only Munc13 isoforms that are expressed in the RBL-2H3 cells, and Munc13-1 is distributed in the cytoplasm, but highly concentrated on the late endosome and/or lysosome. Unexpectedly, antigen-induced degranulation was considerably increased by Munc13-1 knockdown, but decreased by its overexpression. Further, we found that the hypersecretion phenotype of the Munc13-1-knockdown cells was attenuated by simultaneous Munc13-4 knockdown. These results suggested that Munc13-1 has an inhibitory role in antigen-induced mast cell degranulation, which is performed in a Munc13-4-dependent manner.

Serotonin-mediated modulation of acetylcholine-induced intracellular calcium responses in chromaffin cells isolated from the rat adrenal medulla

We examined serotonin (5-HT)-mediated modulation of acetylcholine (ACh)-induced intracellular Ca²⁺ ([Ca²⁺]_i) responses in rat adrenal chromaffin cells using calcium imaging. 5-HT did not induce any [Ca²⁺]_i response in clustered chromaffin cells. However, the magnitude of ACh-induced [Ca²⁺]_i increases in the same specimens was inhibited in the presence of 5-HT. ACh-induced [Ca²⁺]_i increases in chromaffin cells were also inhibited by the 5-HT1A receptor agonist, 8-hydroxy-2-(dipropylamino) tetralin hydrobromide, but were not changed by the 5-HT1B, 5-HT2, or 5-HT3 receptor agonists, CP93129, α-methyl-5-HT, or 1-(m-chlorophenyl) biguanide, respectively. RT-PCR analysis detected the expression of all 5-HT receptor subtype mRNAs, except for 5-HT5 receptors, in extracts of the adrenal medulla. Immunohistochemistry revealed that immunoreactivity for 5-HT1A receptor was located in the chromaffin cells immunoreactive for the biosynthetic enzyme for noradrenaline, dopamine β-hydroxylase. These results suggest that 5-HT inhibits ACh-induced excitability in adrenal chromaffin cells via the 5-HT1A receptor in order to reduce catecholamine release during preganglionic sympathetic stimuli.

Different effect of serotonin on intracellular calcium ion dynamics in the smooth muscle cells between rat posterior ciliary artery and vorticose vein

5-hydroxytriptamine (5-HT: serotonin) is an important transmitter that causes vessel constriction, although few studies have examined the effect of 5-HT on venous smooth muscles. The intracellular Ca(2+) concentration ([Ca(2+)]i) plays an essential role in stimulus-response coupling in numerous tissue/cells including vascular smooth muscle cells. The present study was performed to examine whether differences between arteries and veins in the response to 5-HT can be detected under confocal microscope with respect to [Ca(2+)]i dynamics. In posterior ciliary arteries of rats, 5-HT induced a [Ca(2+)]i increase. The 5-HT-induced responses were caused by both Ca(2+) influx and mobilization. Agonist and antagonist experiments revealed that arterial smooth muscles possess 5-HT1a, 1b, 2 (Gprotein-coupled type) and 5-HT3 (ion channel type) receptors, and that 5-HT2 in particular plays a major role in these responses. For vorticose veins, the 5-HT-induced responses were also caused by both Ca(2+) influx and mobilization. However, the cAMP dependent pathway (5-HT4-7) was found to be significant in vasocontraction with respect to 5-HT in these vessels. Thus, Ca(2+) mobilization was induced by 5-HT2 and 5-HT4-7 in a vessel-dependent manner, whereas Ca(2+) influx universally was induced by 5-HT3. These results indicate that the posterior ciliary arteries and vorticose veins in the same tissue might differ greatly in their responses to stimulus.

P2Y purinoceptors mediate ATP-induced changes in intracellular calcium and amylase release in acinar cells of mouse parotid glands

Adenosine 5'-triphosphate (ATP) can act as an extracellular signal that regulates various cellular functions. The present study aimed to determine which purinoceptors play a role in ATP-induced changes in intracellular Ca(2+) ([Ca(2+)]i) and amylase secretion in mouse parotid glands. ATP induced a steep increase in [Ca(2+)]i in acinar cells. The removal of extracellular Ca(2+) or the use of Ca(2+) channel blockers slightly inhibited this increase. Inhibition of PLCγ by U73122 and of IP3 by xestospongin C did not completely block this increase. The purinoceptor antagonists suramin and reactive blue-2 strongly inhibited the ATP-induced changes in [Ca(2+)]i. 2-MeSATP induced a strong increase in [Ca(2+)]i, while Bz-ATP induced a small [Ca(2+)]i increase, and UTP and α,β-MeATP had no effect. The potency order of ATP analogs (2-MeSATP > ATP >> UTP) suggested that P2Y1 and P2Y12 play a significant role in the cellular response to ATP. RT-PCR revealed that P2X2,4,7 and P2Y1,2,10,12,14 were expressed in acinar cells. Ca(2+)-dependent exocytotic secretion of amylase was detected in parotid glands. These findings indicated that ATP activates P2Y receptors more than P2X receptors at low concentrations. Thus, P2Y receptors were found to be the main receptors involved in Ca(2+)-related cell homeostasis and amylase secretion in mouse parotid glands.

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.

Light and electron microscopic analyses of the high deformability of adhesive toe pads in White's tree frog, Litoria caerulea

White's tree frog (Litoria caerulea) has large, adhesive toe pads that are among the softest of all known biological structures. To explore the morphological basis for the physical properties of the toe pads, the internal microstructure of the toe pads in L. caerulea was examined using both light and transmission electron microscopy. Three design elements that are distinct from other areas of skin were observed. First, the keratinocytes comprising the adhesive surface of the toe pad all contained keratin filament bundles (tonofibrils) exhibiting structural anisotropy. Specifically, the curved conformation of the hierarchical (branching) tonofibrils was characterized by the formation of anastomoses consisting of tonofibrils beneath the adhesive cell surface and stem keratin filament bundles concentrated in the lower-middle part of the dorsal-side of adhesive cells. Second, the cytoplasm of keratinocytes in the most superficial cell layer contained glycoproteins (stained by periodic acid/Schiff reagent) that are considered to confer high viscoelasticity. Third, the dermis contained large lymph spaces interspersed with elastic fibers and collagen fibers, which were relatively sparsely distributed compared to the dorsal skin of the toe pads. The profiles of these structures were easily deformed by the slight application of pressure. These findings reaffirmed that the unique internal architecture of the toe pads in L. caerulea contributed to their remarkable softness and high deformability, which in turn increased the contact area and provided improved adaptability to the local topography of natural surfaces. J. Morphol. 277:1509-1516, 2016. © 2016 Wiley Periodicals, Inc.

Mast cell degranulation is negatively regulated by the Munc13-4-binding small-guanosine triphosphatase Rab37

Mast cell degranulation is regulated by the small guanosine triphosphatases (GTPases) Rab27a and Rab27b, which have distinct and opposing roles: Rab27b acts as a positive regulator through its effector protein Munc13-4, a non-neuronal isoform of the vesicle-priming Munc13 family of proteins, whereas Rab27a acts as a negative regulator through its effector protein melanophilin, by maintaining integrity of cortical filamentous actin (F-actin), a barrier to degranulation. Here we investigated the role of Rab37, one of the Rab GTPases assumed to be implicated in regulated secretion during mast cell degranulation. Using the RBL-2H3 mast cell line, we detected Rab37 on the secretory granules and found that antigen-induced degranulation was extensively increased by either knockdown of Rab37 or overexpression of a dominant-active Rab37 mutant. This hypersecretion phenotype in the Rab37-knockdown cells was suppressed by simultaneous knockdown of Rab27a and Rab27b or of Munc13-4, but not by disruption of cortical F-actin. We further found that Rab37 interacted with Munc13-4 in a GTP-independent manner and formed a Rab27-Munc13-4-Rab37 complex. These results suggest that Rab37 is a Munc13-4-binding protein that inhibits mast cell degranulation through its effector protein, by counteracting the vesicle-priming activity of the Rab27-Munc13-4 system.

P2Y purinoceptors induce changes in intracellular calcium in acinar cells of rat lacrimal glands

Adenosine 5'-triphosphate (ATP) is an extracellular signal that regulates various cellular functions. Cellular secretory activities are enhanced by ATP as well as by cholinergic and adrenergic stimuli. The present study aimed to determine which purinoceptors play a role in ATP-induced changes in the intracellular concentration of calcium ions ([Ca²⁺](i)) and in the fine structure of acinar cells of rat lacrimal glands. ATP induced exocytotic structures, vacuolation and an increase in [Ca²⁺](i) in acinar cells. The removal of extracellular Ca²⁺ or the use of Ca²⁺ channel blockers partially inhibited the ATP-induced [Ca²⁺](i) increase. U73122 (an antagonist of PLC) and heparin (an antagonist of IP₃ receptors) did not completely inhibit the ATP-induced [Ca²⁺](i) increase. P1 purinoceptor agonists did not induce any changes in [Ca²⁺](i), whereas suramin (an antagonist of P2 receptors) completely inhibited ATP-induced changes in [Ca²⁺](i). A P2Y receptor agonist, 2-MeSATP, induced a strong increase in [Ca²⁺](i), although UTP (a P2Y₂,₄,₆ receptor agonist) had no effect, and reactive blue 2 (a P2Y receptor antagonist) resulted in partial inhibition. The potency order of ATP analogs (2-MeSATP > ATP >>> UTP) suggested that P2Y₁ played a significant role in the cellular response to ATP. BzATP (a P2X₇ receptor agonist) induced a small increase in [Ca²⁺](i), but α,β-meATP (a P2X₁,₃ receptor agonist) had no effect. RT-PCR indicated that P2X₂,₃,₄,₅,₆,₇ and P2Y₁,₂,₄,₁₂,₁₄ are expressed in acinar cells. In conclusion, the response of acinar cells to ATP is mediated by P2Y (especially P2Y₁) as well as by P2X purinoceptors.

The effects of diuretics on intracellular Ca2+ dynamics of arteriole smooth muscles as revealed by laser confocal microscopy

The regulation of cytosolic Ca²⁺ homeostasis is essential for cells, including vascular smooth muscle cells. Arterial tone, which underlies the maintenance of peripheral resistance in the circulation, is a major contributor to the control of blood pressure. Diuretics may regulate intracellular Ca²⁺ concentration ([Ca²⁺]_i) and have an effect on vascular tone. In order to investigate the influence of diuretics on peripheral resistance in circulation, we investigated the alteration of [Ca²⁺]_i in testicular arterioles with respect to several categories of diuretics using real-time confocal laser scanning microscopy. In this study, hydrochlorothiazide (100 µM) and furosemide (100 µM) had no effect on the [Ca²⁺]_i dynamics. However, when spironolactone (300 µM) was applied, the [Ca²⁺]_i of smooth muscles increased. The response was considerably inhibited under either extracellular Ca²⁺-free conditions, the presence of Gd³⁺, or with a treatment of diltiazem. After the thapsigargin-induced depletion of internal Ca²⁺ store, the spironolactone-induced [Ca²⁺]_i dynamics was slightly inhibited. Therefore, the spironolactone-induced dynamics of [Ca²⁺]_i can be caused by either a Ca²⁺ influx from extracellular fluid or Ca²⁺ mobilization from internal Ca²⁺ store, with the former being dominant. As tetraethylammonium, an inhibitor of the K⁺ channel, slightly inhibited the spironolactone-induced [Ca²⁺]_i dynamics, the K⁺ channel might play a minor role in those dynamics. Tetrodotoxin, a neurotoxic Na⁺ channel blocker, had no effect, therefore the spironolactone-induced dynamics is a direct effect to smooth muscles, rather than an indirect effect via vessel nerves.

Regional differences in 5-HT receptors in cerebral and testicular arterioles of the rat as revealed by Ca2+ imaging of real-time confocal microscopy: variances by artery size and organ specificity

5-hydroxytriptamine (5-HT) is an important transmitter for vessel constriction. The present study was performed to clarify the effect of 5-HT on smooth muscles in large- and small-sized cerebral and testicular arterioles by confocal microscopy, with special reference to intracellular Ca2+ concentration ([Ca2+]i) dynamics. In cerebral vessels, 5-HT induced a [Ca2+]i increase and the contraction of smooth muscle cells in large- and midsized arterioles (external diameters>50 microm) but not in small-sized arterioles. Conspicuous [Ca2+]i changes by 5-HT were especially observed in the portions close to the cerebral arterial circle, and the 5-HT-induced responses were caused by both Ca2+ influx and mobilization. Experiments using agonists and antagonists also revealed that cerebral arteriole smooth muscles possess 5-HT1a, 1b, 2 (G-protein-coupled type), and 3 (ion channel type) receptors; specifically, 5-HT2 plays a major role in these responses. On the other hand, in testicular vessels, there were few regional differences among responses to 5-HT, and both large- and small-sized arterioles responded to 5-HT. The responses were caused by only Ca2+ mobilization mediated 5-HT1a and 2. These results indicate that arterioles in different tissues may respond to 5-HT in different manners. Regional differences and the size-dependent manner of responses to 5-HT in cerebral blood vessels also indicate that the regulatory mechanism of blood circulation is highly differentiated in each region of the central nervous system.

Microtubule remodeling mediates the inhibition of store-operated calcium entry (SOCE) during mitosis in COS-7 cells

Regulation of the intracellular calcium ion concentration ([Ca(2+)](i)) is critical, because calcium signaling controls diverse and vital cellular processes such as secretion, proliferation, division, gene transcription, and apoptosis. Store-operated calcium entry (SOCE) is the main mechanism through which non-excitable cells replenish and thus maintain this delicate balance. There is limited evidence which indicates that SOCE may be inhibited during mitosis, and the mechanisms leading to the presumed inhibition has not been elucidated. In the present study, we examined and compared the [Ca(2+)](i) dynamics of COS-7 cells in mitotic and non-mitotic phases with special reference paid to SOCE. Laser scanning confocal microscopy to monitor [Ca(2+)](i) dynamics revealed that SOCE was progressively inhibited in mitosis and became virtually absent during the metaphase. We used various cytoskeletal modifying drugs and immunofluorescence to assess the contribution of microtubule and actin filaments in SOCE signaling. Nocodazole treatment caused microtubule reorganization and retraction from the cell periphery that mimicked the natural mitotic microtubule remodeling that was also accompanied by SOCE inhibition. Short exposure to paclitaxel, a microtubule-stabilizing drug, bolstered SOCE, whereas long exposure resulted in microtubule disruption and SOCE inhibition. Actin-modifying drugs did not affect SOCE. These findings indicate that mitotic microtubule remodeling plays a significant role in the inhibition of SOCE during mitosis.

Inhibition of serine/threonine phosphatase enhances arachidonic acid-induced [Ca2+]i via protein kinase A

Arachidonic acid (AA) regulates intracellular calcium concentration ([Ca2+]i) in a variety of cell types including salivary cells. In the present study, the effects of serine/threonine phosphatases on AA-induced Ca(2+) signaling in mouse parotid acini were determined. Mice were euthanized with CO2. Treatment of acini with the serine/threonine phosphatase inhibitor calyculin A blocked both thapsigargin- and carbachol-induced Ca2+ entry but resulted in an enhancement of AA-induced Ca2+ release and entry. Effects were mimicked by the protein phosphatase-1 (PP1) inhibitor tautomycin but were inhibited by the PP2A inhibitor okadaic acid. The protein kinase A (PKA) inhibitor PKI(14-22) significantly attenuated AA-induced enhancement of Ca2+ release and entry in the presence of calyculin A, whereas it had no effect on calyculin A-induced inhibition of thapsigargin-induced Ca2+ responses. The ryanodine receptor (RyR) inhibitor, tetracaine, and StHt-31, a peptide known to competitively inhibit type II PKA regulatory subunit binding to PKA-anchoring protein (AKAP), abolished calyculin A enhancement of AA-induced Ca2+ release and entry. StHt-31 also abolished forskolin potentiation of 4-chloro-3-ethylphenol (4-CEP) and AA on Ca2+ release but had no effect on 8-(4-methoxyphenylthio)-2'-O-methyladenosine-3',5'-cAMP potentiation of 4-CEP responses. Results suggest that inhibition of PP1 results in an enhancement of AA-induced [Ca2+]i via PKA, AKAP, and RyRs.

The role of protease-activated receptors on the intracellular calcium ion dynamics of vascular smooth muscles, with special reference to cerebral arterioles

Protease-activated receptors (PARs) mediate cellular responses to various proteases in numerous cell types, including smooth muscles and the endothelium of blood vessels. To clarify whether the stimulation of PARs induces responses in smooth muscle cells of cerebral arterioles, intracellular Ca2+([Ca2+]i) dynamics and nitric oxide (NO) production during PARs stimulation were investigated in the rat cerebral arterioles by real-time confocal microscopy, since [Ca2+]i and NO are both key factors in the maintenance of strain in blood vessels. Testicular arterioles were also investigated for comparison. In smooth muscle cells of small cerebral arterioles (< 50 microm in diameter), thrombin and PAR1-activating peptide (AP) induced an increase in [Ca2+]i and contraction. The response to PAR1 activation was caused by Ca2+ mobilization from intracellular Ca2+ stores. Trypsin and PAR2-AP induced a decrease in [Ca2+]i in the cells which was considered to be mediated by endothelium-derived NO and/or by promoting a Ca2+ sequestration mechanism. PAR3- and 4-AP had little effect. In contrast to small cerebral arterioles, [Ca2+]i dynamics in smooth muscle cells of large cerebral arterioles (< 150 microm in diameter) or testicular arterioles remained unchanged during PARs activation. The effects of PARs activation on the [Ca2+]i dynamics and the contraction/relaxation of cerebral arterioles are also discussed in relation to the role of proteases in the regional tissue circulation of the brain.

Continuous shipboard sampling system for determination of triple oxygen isotopes and O2/Ar ratio by dual-inlet mass spectrometry

A continuous shipboard sampling system was developed for the determination of the isotopic composition of the triple oxygen isotopes and oxygen to argon (O(2)/Ar) ratios in dissolved air. In this system, dissolved air is separated by a hollow fiber membrane degassing module. This system collects dissolved air quantitatively and rapidly. The sample flow rate through the membrane is critical for the fractionation of the oxygen isotopes and the O(2)/Ar ratio and should be < 2 mL/min. Fractionation of oxygen between the liquid and gas phase of the air-saturated water was found to be similar to that of earlier reports. The advantages of this method over existing techniques include rapid collection of samples (30 min/sample), high efficiency in extraction of gases from the liquid phase, and the lack of a sample preparation step (e.g. degassing).

Response to ATP is accompanied by a Ca2+ influx via P2X purinoceptors in the coronary arterioles of golden hamsters

In the vascular wall, adenosine-5'-triphosphate (ATP) released along with noradrenaline from sympathetic nerve terminals is considered to play an important role in controlling intracellular calcium ion ([Ca2+]i) levels in arteries. The present study examined how vascular smooth muscle cells in coronary arterioles respond to ATP in relation to [Ca2+]i dynamics. For this purpose, the dynamics of [Ca2+]i in the coronary arterioles of golden hamsters was examined by real-time laser scanning confocal microscopy. This technique enabled the visualization of [Ca2+]i changes in response to ATP in the intact coronary arterioles, the ultrastructure of which was well preserved. It was shown that an increase in [Ca2+]i in the arteriole smooth muscle cells was elicited by ATP. While P1 purinoceptor agonists have no effect on this process, P2 purinoceptor agonists were found to induce a [Ca2+]i increase in the smooth muscle cells. Suramin (an antagonist of P2X and P2Y receptors) completely inhibited ATP-induced [Ca2+]i dynamics, but reactive blue 2 (a P2Y receptor antagonist) did not. Uridine-5'-triphosphate (a P2Y receptor agonist) had no effect on [Ca2+]i, but alpha,beta-methylene ATP (a P2X receptor agonist) caused a strong increase in [Ca2+]i. We conclude that smooth muscle cells of the hamster coronary arterioles possess P2X, but not P1 or P2Y purinoceptors. The smooth muscle cells probably respond to extracellular ATP via P2X purinoceptors, resulting in the contraction of the coronary arterioles.

Application of real-time confocal laser scanning microscopy to observe living cells in tissue specimens

Fluorescence microscopy imaging has developed into an important tool for the study of cell structure and function in cell biology. This non-invasive technique permits the characterization, localization and qualitative quantification of free ions, messengers, pH, voltage and other molecules in living cells. The regulation of cytosolic Ca2+ homeostasis is essential for cells. However, most investigations have used cultured or isolated cells as an experimental model and, consequently, provide only limited insight into the mechanisms that operate in tissue in situ. More useful information could be obtained by studying intact tissue specimens. The calcium dynamics of some tissue specimens, such as arteriole smooth muscle cells, supra cervical ganglia and peripheral nerve bundles, were analysed in this study. Real-time confocal microscopy revealed that individual cells exhibited different [Ca2+]i dynamics and the responses to transmitters/modulators were heterogeneous. It is important that the confocal microscopes have good detection performances, due to the reduction of stray light. We conclude that real-time confocal microscopy is a useful tool for investigating structural and functional changes of cells in living tissues, although suitable tissue-preparation is important for these measurements.

Chromatographic Separation of Nitrogen, Argon, and Oxygen in Dissolved Air for Determination of Triple Oxygen Isotopes by Dual-Inlet Mass Spectrometry

A chromatographic system was developed to separate oxygen from nitrogen, argon, carbon dioxide, and water vapor mixture for the determination of precise isotopic ratio measurements of oxygen in dissolved air. This system separates oxygen not only quantitatively but also rapidly as well; typical oxygen separation takes about 30 min. Fractionation of oxygen between liquid and gas phase was found to be similar to that of earlier reports.

ATP-induced [Ca2+]i changes in the human corneal epithelium

ATP, when leaked from damaged cells, is capable of eliciting responses in neighboring cells. A better understanding of the mechanism of this response is essential for designing therapeutic strategies for disease, there have been only a limited number of studies on the effect of ATP on the human cornea. We examined ATP-induced intracellular Ca2+ ([Ca2+]i) changes in the human corneal epithelia, cultured to near confluence. Cells were loaded with the Ca2+ indicators, Indo-1 or Fluo-4, and [Ca2+]i was monitored. ATP was found to induce an increase in [Ca2+]i, which was initiated from the perinuclear region and the nuclear envelope per se, and then propagated gradually towards the periphery. Intranuclear Ca2+ was momentarily increased. UTP elicited an identical response, but adenosine and alpha, beta-methylene ATP had no effect. Pretreatment with U73122 or thapsigargin inhibited the ATP-induced increase in [Ca2+]i. When a cell was topically stimulated with ATP, the [Ca2+]i increase spread beyond the cell boundary. The intercellular communications that accompanied the [Ca2+]i changes were inhibited by octanol. We conclude that extracellular ATP in the human cornea caused the mobilization of Ca2+ from intracellular Ca2+ stores (e.g. the endoplasmic reticulum and nuclear envelope) via P2Y purinoceptors of the epithelial cell. The response to ATP appears to spread to neighboring regions through gap junctions in the epithelium.

Adenosine-5'-triphosphate-induced intracellular calcium changes through gap-junctional communication in the corneal epithelium

PURPOSE

To investigate intercellular communication in the corneal epithelium, changes in the concentration of intracellular Ca(2+) ([Ca(2+)](i) ) induced by adenosine-5'-triphosphate (ATP) were analyzed.

METHODS

Rabbit corneal epithelia were loaded with Ca(2+) indicators and then stimulated by ATP (10 microM). [Ca(2+)](i) changes were monitored by means of conventional fluorescence and real-time confocal microscopy. The localization of connexin 50 (Cx50) was also immunohistochemically examined.

RESULTS

ATP was found to induce [Ca(2+)](i) increase, which was often synchronized among adjacent cells. When wing cells were topically stimulated by treatment with ATP, the [Ca(2+)](i) increase spread to adjacent wing cells, but significant increase in [Ca(2+)](i) in the superficial and the basal cell layers was not observed. The propagation of the [Ca(2+)](i) change was suppressed in the presence of octanol (1 mM), a gap junction inhibitor. Immunohistochemical staining of Cx50 was strongly detected in the wing and basal cells, but faintly in the superficial cells.

CONCLUSIONS

There was intercellular communication accompanied by [Ca(2+)](i) changes in wing cell layers, but not in superficial or basal cell layers. The difference in [Ca(2+)](i) changes among the layers of the corneal epithelium suggests that the response of each cell layer plays a distinct role in proliferation and differentiation during recovery of the corneal epithelium.

Comparison of the effect of ATP on intracellular calcium ion dynamics between rat testicular and cerebral arteriole smooth muscle cells

Adenosine 5'-triphosphate (ATP), when released from neuronal and non-neuronal tissues, interacts with cell surface receptors produces a broad range of physiological responses. The goal of the present study was to examine the issue of whether vascular smooth muscle cells respond to ATP. To this end, the dynamics of the intracellular concentration of calcium ions ([Ca(2+)](i)) in smooth muscle cells in testicular and cerebral arterioles was examined by laser scanning confocal microscopy. ATP produced an increase in [Ca(2+)](i) in arteriole smooth muscle cells. While P1 purinoceptor agonists had no effect on this process, P2 purinoceptor agonists induced a [Ca(2+)](i) increase and a P2 purinoceptor antagonist, suramin, completely inhibited ATP-induced [Ca(2+)](i) dynamics in both arteriole smooth muscle cells. In testicular arterioles, Ca(2+) channel blockers and the removal of extracellular Ca(2+), but not thapsigargin pretreatment, abolished the ATP-induced [Ca(2+)](i) dynamics. In contrast, Ca(2+) channel blockers and the removal of extracellular Ca(2+) did not completely inhibit ATP-induced [Ca(2+)](i) dynamics in cerebral arterioles. Uridine 5'-triphosphate caused an increase in [Ca(2+)](i) only in cerebral arterioles and alpha,beta-methylene ATP caused an increase in [Ca(2+)](i) in both testicular and cerebral arterioles. We conclude that testicular arteriole smooth muscle cells respond to extracellular ATP via P2X purinoceptors and that cerebral arteriole smooth muscle cells respond via P2X and P2Y purinoceptors.

Application of real-time confocal microscopy to intracellular calcium ion dynamics in rat arterioles

The regulation of cytosolic Ca(2+) homeostasis is essential for cells, including vascular smooth muscle cells. Arterial tone, which underlies the maintenance of peripheral resistance in the circulation, is a major contributor to the control of blood pressure. Confocal microscopy was employed to study the alteration in intracellular calcium ion concentration ([Ca(2+)](i)) in arterioles (external diameters <100 microm) with respect to selected modifying reagents. 5-Hydroxytryptamine (1 microM), ATP (10 microM), and endothelin 1-3 (5 nM) elicited an increase in [Ca(2+)](i) in most arteriole smooth muscle cells. The [Ca(2+)](i) increase sometimes propagated in an intercellular manner. When noradrenaline (10 microM) was used as a stimulant, [Ca(2+)](i) increase was observed only in a portion of the smooth muscle cells. It was also noted that the reaction of these cells with respect to ATP is different between testis and brain arterioles; the [Ca(2+)](i) increase in testicular arterioles is dependent on Ca(2+) influx from extracellular space, whereas in cerebral arterioles it plays a role in both the influx of extracellular Ca(2+) and the release of Ca(2+) from intracellular stores (i.e., sarco/endoplasmic reticulum). These results indicate that arterioles in different tissues may differ greatly in their responses. Real-time confocal microscopy was found to be a useful tool for investigating the structural and functional changes in living tissues.

Mutations of either or both Cys876 and Cys888 residues of sarcoplasmic reticulum Ca2+-ATPase result in a complete loss of Ca2+ transport activity without a loss of Ca2+-dependent ATPase activity. Role of the CYS876-CYS888 disulfide bond

Disulfide-containing peptides in pepsin digest of sarcoplasmic reticulum vesicles were identified by using a fluorogenic thiol-specific reagent 4-fluoro-7-sulfamoylbenzofurazan and a reductant tributylphosphine. Sequencing of the purified peptides revealed the presence of a Cys(876)-Cys(888) disulfide bond on the luminal loop connecting the 7th and 8th transmembrane helices (loop 7-8) of the Ca(2+)-ATPase (SERCA1a). We substituted either or both of these cysteine residues with alanine and made three mutants (C876A, C888A, C876A/C888A), in which the disulfide bond is disrupted. The mutants and the wild type were expressed in COS-1 cells, and functional analysis was performed with the microsomes isolated from the cells. Electrophoresis performed under reducing and non-reducing conditions confirmed the presence of Cys(876)-Cys(888) disulfide bond in the expressed wild type. All the three mutants possessed high Ca(2+)-ATPase activity. In contrast, no Ca(2+) transport activity was detected with these mutants. These mutants formed almost the same amount of phosphoenzyme intermediate as the wild type from ATP and from P(i). Detailed kinetic analysis showed that the three mutants hydrolyze ATP in the mechanism well accepted for the Ca(2+)-ATPase; activation of the catalytic site upon high affinity Ca(2+) binding, formation of ADP-sensitive phosphoenzyme, subsequent rate-limiting transition to ADP-insensitive phosphoenzyme, and hydrolysis of the latter phosphoenzyme. It is likely that the pathway for delivery of Ca(2+) from the binding sites into the lumen of vesicles is disrupted by disruption of the Cys(876)-Cys(888) disulfide bond, and therefore that the loop 7-8 having the disulfide bond is important for formation of the proper structure of the Ca(2+) pathway.

Effects of ATP on intracellular calcium dynamics of neurons and satellite cells in rat superior cervical ganglia

Adenosine 5'-triphosphate (ATP) which is released from neuronal and non-neuronal tissues interacts with cell surface receptors to produce a broad range of physiological responses. The present study addressed the issue of whether the cells of the superior cervical ganglia (SCG) respond to ATP. To this end, the dynamics of the intracellular calcium ion concentration ([Ca2+]i) of neurons and satellite cells in intact SCG was analyzed by laser scanning confocal microscopy. ATP produced an increase of [Ca2+]i in both neurons and satellite cells; initially, ATP elicited [Ca2+]i increase in satellite cells and, subsequently, a [Ca2+]i change in neurons was observed. P1 purinoceptor agonists had no effect on this process, but P2 purinoceptor agonists induced [Ca2+]i increase and suramin totally inhibited ATP-induced [Ca2+]i dynamics in both neurons and satellite cells. In satellite cells, Ca2+ channel blockers and the removal of extracellular Ca2+, but not thapsigargin pretreatment, abolished ATP-induced [Ca2+]i dynamics. In contrast, thapsigargin pretreatment abolished ATP-induced [Ca2+]i dynamics in neurons. Reactive blue-2 inhibited the ATP-induced reaction on neurons alone. Uridine 5'-triphosphate caused a [Ca2+]i increase in neurons and alpha,beta-methylene ATP caused a [Ca2+]i increase in satellite cells. We concluded that neurons respond to extracellular ATP mainly via P2Y purinoceptors and that satellite cells respond via P2X purinoceptors.

Effects of ATP on intracellular calcium dynamics of the perineurium of peripheral nerve bundles

Adenosine-5'-triphosphate (ATP) released from damaged cells can affect functions of adjacent cells. Injuries of peripheral tissue stimulate nerves, but effect of ATP on the nerve bundles is still speculative. Peripheral nerves are surrounded by perineurium, therefore the response of perineurium may be a first event of nerve stimulation at tissue injuries. The aim of the present study is to clarify whether the perineurium responds to ATP. To this end, we analyzed the dynamics of the intracellular calcium concentration ([Ca2+]i) of perineurial cells by confocal microscopy. ATP induced a [Ca2+]i increase of perineurial cells. Ca2+ channel blockers and removing of extracellular Ca2+, but not thapsigargin pretreatment, abolished ATP-induced [Ca2+]i dynamics. This indicated that the [Ca2+]i increase was due to an influx of extracellular Ca2+. Adenosine-5'-diphosphate also elicited an increase of [Ca2+]i, but P1 receptor agonists had few effects on [Ca2+]i dynamics. Suramin (an antagonist of P2X and P2Y receptors) totally inhibited ATP-induced [Ca2+]i dynamics, but reactive blue 2 (a P2Y receptor antagonist) did not. Uridine-5'-triphosphate (a P2Y receptor agonist) induced no significant change in [Ca2+]i, but alpha,beta-methylene ATP (a P2X receptor agonist) caused a [Ca2+]i increase. In conclusion, perineurial cells respond to extracellular ATP mainly via P2X receptors.

Effect of low temperatures on compound 48/80-induced intracellular Ca2+ changes and exocytosis of rat peritoneal mast cells

It has been well documented that compound 48/80-induced exocytosis of mast cells is accompanied by changes in intracellular Ca2+ concentration ([Ca2+]i) showing a biphasic pattern: an initial phase which constitutes an abrupt increase, followed by a plateau phase. The former is caused by Ca2+ release from intracellular Ca2+ stores, and the latter is the result of secondary Ca2+ influx. Low temperatures lead to the inhibition of exocytosis, but the precise mechanism remains unclear. The present study aims to reveal whether [Ca2+]i changes are affected by the environmental temperature. To this end, we developed a novel imaging method to record [Ca2+]i changes and exocytotic processes simultaneously. Rat peritoneal mast cells were loaded by Indo-1/AM or Fluo-3/AM for measuring [Ca2+]i, and the exocytosed granule matrices were stained by sulforhodamine-B. Cells were stimulated by compound 48/80, and [Ca2+]i changes and exocytosis were recorded by means of a real-time confocal microscope. At 37 degrees C, [Ca2+]i changes in stimulated mast cells showed a sustained plateau phase. Granule discharge was observed at the cell surface, and, in addition, most of the intracellular granule matrices were involved in compound exocytosis. The granule discharge and compound exocytosis proceeded over a period of a few minutes. At 4 degrees C, the plateau phase of [Ca2+]i changes declined rapidly, although the initial phase was not suppressed. Granule discharge occurred at the cell surface, but compound exocytosis ceased within a few minutes. These findings indicate that a low temperature inhibits compound exocytosis which can be caused by Ca2+ influx. The present imaging method represents a powerful tool for investigating the stimulus-secretion coupling of mast cells.

Deletions or specific substitutions of a few residues in the NH(2)-terminal region (Ala(3) to Thr(9)) of sarcoplasmic reticulum Ca(2+)-ATPase cause inactivation and rapid degradation of the enzyme expressed in COS-1 cells

Amino acid residues in the NH(2)-terminal region (Glu(2) - Ala(14)) of adult fast twitch skeletal muscle sarcoplasmic reticulum Ca(2+)-ATPase (SERCA1a) were deleted or substituted, and the mutants were expressed in COS-1 cells. Deletion of any single residue in the Ala(3)-Ser(6) region or deletion of two or more consecutive residues in the Ala(3)-Thr(9) region caused strongly reduced expression. Substitution mutants A4K, A4D, and H5K also showed very low expression levels. Deletion of any single residue in the Ala(3)-Ser(6) region caused only a small decrease in the specific Ca(2+) transport rate/mg of SERCA1a protein. In contrast, other mutants showing low expression levels had greatly reduced specific Ca(2+) transport rates. In vitro expression experiments indicated that translation, transcription, and integration into the microsomal membranes were not impaired in the mutants that showed very low expression levels in COS-1 cells. Pulse-chase experiments using [(35)S]methionine/cysteine labeling of transfected COS-1 cells demonstrated that degradation of the mutants showing low expression levels was substantially faster than that of the wild type. Lactacystin, a specific inhibitor of proteasome, inhibited the degradation accelerated by single-residue deletion of Ala(3). These results suggest that the NH(2)-terminal region (Ala(3) -Thr(9)) of SERCA1a is sensitive to the endoplasmic reticulum-mediated quality control and is thus critical for either correct folding of the SERCA1a protein or stabilization of the correctly folded SERCA1a protein or both.

Mutations of Arg198 in sarcoplasmic reticulum Ca2+-ATPase cause inhibition of hydrolysis of the phosphoenzyme intermediate formed from inorganic phosphate

Arg198 of sarcoplasmic reticulum Ca2+-ATPase was substituted with lysine, glutamine, glutamic acid, alanine, and isoleucine by site-directed mutagenesis. Kinetic analysis was performed with microsomal membranes isolated from COS-1 cells which were transfected with the mutated cDNAs. The rate of dephosphorylation of the ADP-insensitive phosphoenzyme was determined by first phosphorylating the Ca2+-ATPase with 32Pi and then diluting the sample with non-radioactive Pi. This rate was reduced substantially in the mutant R198Q, more strongly in the mutants R198A and R1981, and most strongly in the mutant R198E, but to a much lesser extent in R198K. The reduction in the rate of dephosphorylation was consistent with the observed decrease in the turnover rate of the Ca2+-ATPase accompanied by the steady-state accumulation of the ADP-insensitive phosphoenzyme formed from ATP. These results indicate that the positive charge and high hydrophilicity of Arg198 are critical for rapid hydrolysis of the ADP-insensitive phosphoenzyme.

Application of real-time confocal microscopy for observation of living cells in tissue specimens

Measurement of intracellular Ca2+ concentration ([Ca2+]i) has been a fundamental technique in cell biology. However, most investigations have used cultured or isolated cells as an experimental model, and consequently can provide only limited insight into the mechanisms that operate in tissue in situ. Useful information may be obtained by studying intact tissue specimens. High-speed confocal microscopes that can acquire digital images at video rate have recently been developed. These confocal microscopes which can acquire data in real-time enable [Ca2+]i dynamics of individual cells in intact tissue specimens to be observed. The present paper examines the use of fluorescent microscopy and confocal microscopy for [Ca2+]i imaging of living tissue. We analyzed the dynamics of the duodenal gland, lacrimal gland, intestinal smooth muscles, arterioles, myenteric plexus, and dorsal root ganglion. In these specimens, individual cells exhibited different [Ca2+]i dynamics, and the responses to transmitters/modulators were heterogeneous. In conclusion, real-time imaging provides a useful tool for observing dynamic changes in cells in situ, and it may lead to improve understanding tissue physiology.

Modification of histidine 5 in sarcoplasmic reticulum Ca2+-ATPase by diethyl pyrocarbonate causes strong inhibition of formation of the phosphoenzyme intermediate from inorganic phosphate

Sarcoplasmic reticulum vesicles were modified with diethyl pyrocarbonate (DEPC), a histidine-modifying reagent. Phosphoenzyme formation from Pi in the Ca2+-ATPase (reversal of hydrolysis of the phosphoenzyme intermediate) was almost completely inhibited by this modification. Tight binding of F- and Mg2+ and high affinity binding of vanadate in the presence of Mg2+, both of which produce transition state analogs for phosphoenzyme formation from the magnesium-enzyme-phosphate complex, were also inhibited. Formation of the phosphoenzyme from acetyl phosphate in the forward reaction was only weakly inhibited, but hydrolysis of the phosphoenzyme was strongly inhibited. The enzyme was protected by tight binding of F- and Mg2+ or by high affinity binding of vanadate in the presence of Mg2+ against the DEPC-induced inhibition of phosphoenzyme formation from Pi. The enzyme was also protected by tight binding of F- and Mg2+ against the DEPC-induced inhibition of phosphoenzyme hydrolysis. Peptide mapping of the tryptic digests, detection of peptides containing DEPC-modified histidine by UV absorption at 240 nm, amino acid analysis, sequencing, and mass spectrometry showed that His-5 was a single major residue protected by the above transition state analogs against the modification with DEPC. These results indicate that modification of His-5 with DEPC is responsible for the DEPC-induced inhibition of phosphoenzyme formation from Pi and of phosphoenzyme hydrolysis and suggest that His-5 is located in or very close to the catalytic site in the transition state for phosphoenzyme formation from the magnesium-enzyme-phosphate complex and is likely involved in the catalytic process of this reaction step.

Modification of arginine-198 in sarcoplasmic reticulum Ca2+-ATPase by 1,2-cyclohexanedione causes inhibition of formation of the phosphoenzyme intermediate from inorganic phosphate

Sarcoplasmic reticulum vesicles were modified with 1,2-cyclohexanedione (CHD), a specific arginine-modifying reagent, in sodium borate (pH 8.0 or 8.8). Phosphoenzyme formation from Pi in the Ca2+-ATPase (reversal of hydrolysis of the phosphoenzyme intermediate) was almost completely inhibited by the modification with CHD. Tight binding of F- and Mg2+ and high affinity binding of vanadate in the presence of Mg2+, either of which produces a transition state analog for phosphoenzyme formation from the magnesium-enzyme-phosphate complex, were also markedly inhibited. In contrast, phosphoenzyme formation from acetyl phosphate in the forward reaction was unaffected. The enzyme was appreciably protected by tight binding of F- and Mg2+ or by high affinity binding of vanadate in the presence of Mg2+, but not by the presence of 20 mM MgCl2 alone or 150 mM Pi alone, against the CHD-induced inhibition of phosphoenzyme formation from Pi. Peptide mapping of the tryptic digests, detection of peptides containing CHD-modified arginyl residues with Girard's reagent T, sequencing, and mass spectrometry showed that Arg-198 was a single major residue protected by tight binding of F- and Mg2+ against the modification with CHD. These results indicate that modification of Arg-198 with CHD is responsible for at least a part (the portion reduced by the transition state analogs) of the CHD-induced inhibition of phosphoenzyme formation from Pi and suggest that Arg-198 is located in or close to the catalytic site in the transition state for phosphoenzyme formation from the magnesium-enzyme-phosphate complex.