Successful bladder-sparing partial cystectomy for muscle-invasive domal urothelial carcinoma with sarcomatoid differentiation: a case report

High-grade (HG) urothelial carcinoma (UC) with variant histology has historically been managed conservatively. The presented case details a solitary lesion of muscle-invasive bladder cancer (MIBC) with sarcomatoid variant (SV) histology treated by partial cystectomy (PC) and adjuvant chemotherapy. A 71-year-old male with a 15-pack year smoking history presented after outside transurethral resection of bladder tumor (TURBT). Computerized tomography imaging was negative for pelvic lymphadenopathy, a 2 cm broad-based papillary tumor at the bladder dome was identified on office cystoscopy. Complete staging TURBT noted a final pathology of invasive HG UC with areas of spindle cell differentiation consistent with sarcomatous changes and no evidence of lymphovascular invasion. The patient was inclined toward bladder-preserving options. PC with a 2 cm margin and bilateral pelvic lymphadenectomy was performed. Final pathology revealed HG UC with sarcomatoid differentiation and invasion into the deep muscularis propria, consistent with pathologic T2bN0 disease, a negative margin, and no lymphovascular invasion. Subsequently, the patient pursued four doses of adjuvant doxorubicin though his treatment was complicated by hand-foot syndrome. At 21 months postoperatively, the patient developed a small (<1 cm) papillary lesion near but uninvolved with the left ureteral orifice. Blue light cystoscopy and TURBT revealed noninvasive low-grade Ta UC. To date, the patient has no evidence of HG UC recurrence; 8 years after PC. Patient maintains good bladder function and voiding every 3-4 h with a bladder capacity of around 350 ml. Surgical extirpation with PC followed by adjuvant chemotherapy may represent a durable solution for muscle invasive (pT2) UC with SV histology if tumor size and location are amenable. Due to the sparse nature of sarcomatous features within UC, large multicenter studies are required to further understand the clinical significance and optimal management options for this variant histology.

Matrilysin/matrix metalloproteinase-7(MMP7) cleavage of perlecan/HSPG2 creates a molecular switch to alter prostate cancer cell behavior

Perlecan/HSPG2, a large heparan sulfate (HS) proteoglycan, normally is expressed in the basement membrane (BM) underlying epithelial and endothelial cells. During prostate cancer (PCa) cell invasion, a variety of proteolytic enzymes are expressed that digest BM components including perlecan. An enzyme upregulated in invasive PCa cells, matrilysin/matrix metalloproteinase-7 (MMP-7), was examined as a candidate for perlecan proteolysis both in silico and in vitro. Purified perlecan showed high sensitivity to MMP-7 digestion even when fully decorated with HS or when presented in native context connected with other BM proteins. In both conditions, MMP-7 produced discrete perlecan fragments corresponding to an origin in immunoglobulin (Ig) repeat region domain IV. While not predicted by in silico analysis, MMP-7 cleaved every subpart of recombinantly generated perlecan domain IV. Other enzymes relevant to PCa that were tested had limited ability to cleave perlecan including prostate specific antigen, hepsin, or fibroblast activation protein α. A long C-terminal portion of perlecan domain IV, Dm IV-3, induced a strong clustering phenotype in the metastatic PCa cell lines, PC-3 and C4-2. MMP-7 digestion of Dm IV-3 reverses the clustering effect into one favoring cell dispersion. In a C4-2 Transwell® invasion assay, perlecan-rich human BM extract that was pre-digested with MMP-7 showed loss of barrier function and permitted a greater level of cell penetration than untreated BM extract. We conclude that enzymatic processing of perlecan in the BM or territorial matrix by MMP-7 as occurs in the invasive tumor microenvironment acts as a molecular switch to alter PCa cell behavior and favor cell dispersion and invasiveness.

Inhibition of Ca2+ influx by surfactant in NR8383 alveolar macrophages

OBJECTIVE

Pulmonary surfactants reduce alveolar surface tension and alter inflammatory cell function. We studied the effects of surfactant preparations on Ca2+ influx regulated by protein kinase C (PKC) and mitogen-activated protein kinases (MAPK) and cytokine secretion in the alveolar macrophage (AM) cell line NR8383.

METHODS

Fura-2-loaded AMs were stimulated with zymosan (200 microg/ml), 1,2-dioctanoyl-sn-glycerol (DOG, 20 microM) or C6-ceramide (C6C, 10 microM) in the presence of exogenous surfactants (beractant, calfactant or colfosceril) or surfactant phospholipid (dipalmitoyl phosphatidylcholine, DPPC), at 250 microg/ml phospholipid and changes in cytosolic free Ca2+ (Delta[Ca2+]i) and cytokines were measured.

RESULTS

Zymosan-induced Delta[Ca2+]i (117 +/- 5 nM) at 3 min was reduced (p <0.001) by beractant (50 +/- 6 nM), colfosceril (61 +/- 2 nM), calfactant (46 +/- 5 nM), and DPPC (52 +/- 5 nM). Beractant inhibited the Delta[Ca2+]i by PKC stimulation with DOG and all preparations reduced the MAPK-induced Ca2+ influx by C6C. Beractant and Ca2+ channel blocker SKF 96365 (10 microM) together abolished the zymosan-stimulated Delta[Ca2+]i. Zymosan-stimulated TNF-alpha and IL-1beta secretion was also inhibited by surfactant pretreatment.

CONCLUSIONS

These results indicate that exogenous surfactant inhibits Ca2+ influx and cytokine secretion in zymosan-stimulated AMs. This anti-inflammatory activity may be through an interaction with downstream signaling elements or Ca2+ channels.

Anatomical and functional connectivity of the transected ulnar nerve after accessory nerve neurotization in the cat

AIM

The objective of this experimental study was to test the capacity of accessory nerve motoneurons to innervate muscles of the ulnar nerve territory after direct anastomosis.

METHODS

This study used 22 cats in two groups: experimental group (15 cats) and control group (7 cats). The first one was followed during twelve months using electromyographic records every two months postsurgery; muscle and nerve histological assessment and counting horseradish peroxidase-labeled motoneurons.

RESULTS

Our results showed that reinnervation was achieved in 12/15 nerves. The number of HRP labelled medullar motoneurons after anastomosis showed a significant statistic difference with a simple ulnar nerve transection; there was no significant statistic difference in labelling between the group with an anastomosis and the one with a simple accessory nerve transection.

CONCLUSIONS

Direct anastomosis between the spinal accessory nerve and the ulnar nerve is achievable and thus, the accessory spinal nerve is another possible choice for correcting the motor deficit arising from lower brachial plexus avulsion, but the limited number of motoneurons would only allow partial reinnervation..

A reservable antiadhesion barrier gel reduces the perineural adhesions in rats after anastomosis

AIM

The objective of this experimental study was to assess the effectiveness of ADCON T/N in reducing perinerural adhesions when applied around a previously exposed and then anastomosed peripheral nerve in a rat model.

METHODS

Sixteen adult 8-month-old male Wistar rats were used for this study. After the ulnar nerve was exposed bilaterally, the nerves were sectioned and anastomosised. ADCON T/N gel was applied around the nerve suture on 1 limb, while the contralateral limb was left untreated (sham operated control). Treatments were administered according to a randomised schedule revealed to the operator only after the perineural adhesions observed during the 2nd operation had been dissected and complete haemostasis achieved. In other group of 4 Wistar rats, the ulnar nerve was sectioned and the 2 ends connected with a 5 mm silastic tube that was placed bilaterally in each rat but on only one side, chosen randomly, was the nerve treated with ADCON TN and placed within the tube on that side.

RESULTS

Three months after the 1st operation, the same nerves were exposed again in all animals under general anesthesia before microsurgical external neurolysis. The neurolysis sites in 16 rats were evaluated by blinded surgical dissection immediately before death. Parameters examined included: quality of wound healing, possible adverse effects, presence of residual implant material and perineural adhesions. Perineural adhesions around the ulnar nerve were visually scored using a 4-point qualitative scale (Mean 2.81 without gel, and 1.18 with ADCON T/N. p=0.017). There was no evidence of persistence of residual implant material in the ADCON T/N treated sites. No significant difference between the average density of myelinated axons was observed in either group. All ADCON T/N treated rats (4 animals) showed axonal growth through the tube connecting the 2 ends.

CONCLUSION

ADCON-TN decreased fibrosis around the nerve anastomosis sites and did not impede growth between the severed ends of the axons. If reoperation becomes necessary, a reduction of fibrosis would facilitate access to the old site and decrease the risk of nerve lesions.

Effects of radiation on Ca2+signaling in salivary epithelial cell lines transfected with Bcl-2 and Bcl-XL

The effects of radiation on the Ca2+ signaling system in HSY cells transfected with the Bcl-2 or Bcl-XL gene were studied. Bcl-2 overexpression did not alter carbachol (CCh)-elicited initial increase in cytosolic free Ca2+ concentrations ([Ca2+]i), but Bcl-XL overexpression dramatically reduced this response. Exposure to 10 Gy gamma-ray did not alter basal [Ca2+]i. By contrast, the CCh-stimulated initial [Ca2+]i increase was reduced at 0.5 and 4 h post-irradiation in all cell types and remained decreased at 24 h in wild-type and control-transfected cells, but recovered in Bcl-2- and Bcl-XL-transfectants. The formation of inositol 1,4,5-trisphosphate (IP3) in response to CCh at 4-h post-irradiation was decreased in wild-type and control-transfected cells, but not in Bcl-2 and Bcl-XL transfectants. The capacity of the IP3-sensitive Ca2+ store was significantly reduced by radiation in all cells except Bcl-XL transfectants. Ca2+ influx after stimulation with CCh was suppressed by exposure to radiation in wild-type and control-transfected cells, but not in Bcl-2- and Bcl-XL-transfectants. However, radiation enhanced Ca2+ influx activated by thapsigargin in all cell types. These results suggest that 1) radiation diminishes IP3 formation and Ca2+ release in response to CCh, but potentiates the store-operated Ca2+ influx; and 2) overexpression of Bcl-2 or Bcl-XL partially protects cells from radiation-induced inhibition of Ca2+ signaling.

Regulation of Ca(2+) signals in a parotid cell line Par-C5

The Ca(2+) signaling system in an established immortalized rat parotid acinar cell line, Par-C5, was examined using the Ca(2+)-sensitive fluorescent indicator fura-2 and by measuring inositol 1,4,5-trisphosphate (IP(3)) formation. Agonist-induced increase in intracellular Ca(2+) ([Ca(2+)](i)) by mobilization of intracellular stores and influx across the cell membrane was stimulated by acetylcholine (ACh) and ATP, whereas noradrenaline-(NA)-induced a small [Ca(2+)](i) increase mediated primarily by release from intracellular Ca(2+) stores. [Ca(2+)](i) increase by ACh and ATP was mediated through the phosphoinositide signal pathway since both agonists significantly increased 1,4,5-IP(3) formation and Ca(2+) mobilization was abolished by the phospholipase C inhibitor U73122. In Ca(2+)-free medium, ACh or ATP discharged the IP(3)-sensitive Ca(2+) store and essentially abolished subsequent [Ca(2+)](i) response to thapsigargin (TG). Exposure to ionomycin and monensin after TG induced a further mobilization of Ca(2+), suggesting IP(3)-insensitive stores are present. Furthermore, depletion of IP(3)-sensitive Ca(2+) stores by TG, ACh and ATP enhanced plasmalemmal Ca(2+)-entry pathways. Exposure to tumor necrosis factor-alpha (TNF-alpha), a cytokine associated with lymphocyte invasion of salivary epithelial cells in autoimmune disorders, significantly reduced ACh-stimulated Ca(2+) mobilization. TNF-alpha inhibitory effect on Ca(2+) mobilization was not directly due to an interaction on muscarinic receptors since ACh-induced 1,4,5-IP(3) formation was not altered. These results in the Par-C5 cell line indicate 1) [Ca(2+)](i) is regulated by muscarinic and P2Y-nucleotide receptors and partly by alpha(1)-adrenergic receptors; 2) IP(3)-sensitive and -insensitive Ca(2+) stores exist; 3) Ca(2+) influx activated by ACh, ATP or TG is mediated by the store-operated Ca(2+) entry pathway; and 4) muscarinic agonist-stimulated Ca(2+) mobilization is altered by the cytokine TNF-alpha.

Characterization of the calcium signaling system in the submandibular cell line SMG-C6

Establishment of salivary cell lines retaining normal morphological and physiological characteristics is important in the investigation of salivary cell function. A submandibular gland cell line, SMG-C6, has recently been established. In the present study, we characterized the phosphoinositide (PI)-Ca2+ signaling system in this cell line. Inositol 1,4,5-trisphosphate(1,4,5-IP3) formation, as well as Ca2+ storage, release, and influx in response to muscarinic, alpha1-adrenergic, P2Y-nucleotide, and cytokine receptor agonists were determined. Ca2+ release from intracellular stores was strongly stimulated by acetylcholine (ACh) and ATP, but not by norepinephrine (NA), epidermal growth factor (EGF), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNFalpha). Consistently, 1, 4,5-IP3 formation was dramatically stimulated by ACh and ATP. ACh-stimulated cytosolic free Ca2+ concentration [Ca2+]i increase was inhibited by ryanodine, suggesting that the Ca2+-induced Ca2+ release mechanism is involved in the ACh-elicited Ca2+ release process. Furthermore, ACh and ATP partially discharged the IP3-sensitive Ca2+ store, and a subsequent exposure to thapsigargin (TG) induced further [Ca2+]i increase. However, exposure to TG depleted the store and a subsequent stimulation with ACh or ATP did not induce further [Ca2+]i increase, suggesting that ACh and ATP discharge the same storage site sensitive to TG. As in freshly isolated submandibular acinar cells, exposure to ionomycin and monensin following ACh or TG induced further [Ca2+]i increase, suggesting that IP3-insensitive stores exist in SMG-C6 cells. Ca2+ influx was activated by ACh, ATP, or TG, and was significantly inhibited by La3+, suggesting the involvement of store-operated Ca2+ entry (SOCE) pathway. These results indicate that in SMG-C6 cells: (i) Ca2+ release is triggered by muscarinic and P2Y-nucleotide receptor agonists through formation of IP3; (ii) both the IP3-sensitive and -insensitive Ca2+ stores are present; and (iii) Ca2+ influx is mediated by the store-operated Ca2+ entry pathway. We conclude that Ca2+ regulation in SMG-C6 cells is similar to that in freshly isolated SMG acinar cells; therefore, this cell line represents an excellent SMG cell model in terms of intracellular Ca2+ signaling.

Characterization of the calcium signaling system in the submandibular cell line SMG-C6

Establishment of salivary cell lines retaining normal morphological and physiological characteristics is important in the investigation of salivary cell function. A submandibular gland cell line, SMG-C6, has recently been established. In the present study, we characterized the phosphoinositide (PI)-Ca2+ signaling system in this cell line. Inositol 1,4,5-trisphosphate(1,4,5-IP3) formation, as well as Ca2+ storage, release, and influx in response to muscarinic, alpha1-adrenergic, P2Y-nucleotide, and cytokine receptor agonists were determined. Ca2+ release from intracellular stores was strongly stimulated by acetylcholine (ACh) and ATP, but not by norepinephrine (NA), epidermal growth factor (EGF), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNFalpha). Consistently, 1, 4,5-IP3 formation was dramatically stimulated by ACh and ATP. ACh-stimulated cytosolic free Ca2+ concentration [Ca2+]i increase was inhibited by ryanodine, suggesting that the Ca2+-induced Ca2+ release mechanism is involved in the ACh-elicited Ca2+ release process. Furthermore, ACh and ATP partially discharged the IP3-sensitive Ca2+ store, and a subsequent exposure to thapsigargin (TG) induced further [Ca2+]i increase. However, exposure to TG depleted the store and a subsequent stimulation with ACh or ATP did not induce further [Ca2+]i increase, suggesting that ACh and ATP discharge the same storage site sensitive to TG. As in freshly isolated submandibular acinar cells, exposure to ionomycin and monensin following ACh or TG induced further [Ca2+]i increase, suggesting that IP3-insensitive stores exist in SMG-C6 cells. Ca2+ influx was activated by ACh, ATP, or TG, and was significantly inhibited by La3+, suggesting the involvement of store-operated Ca2+ entry (SOCE) pathway. These results indicate that in SMG-C6 cells: (i) Ca2+ release is triggered by muscarinic and P2Y-nucleotide receptor agonists through formation of IP3; (ii) both the IP3-sensitive and -insensitive Ca2+ stores are present; and (iii) Ca2+ influx is mediated by the store-operated Ca2+ entry pathway. We conclude that Ca2+ regulation in SMG-C6 cells is similar to that in freshly isolated SMG acinar cells; therefore, this cell line represents an excellent SMG cell model in terms of intracellular Ca2+ signaling.

Ion transport in an immortalized rat submandibular cell line SMG-C6

The immortalized rat submandibular epithelial cell line, SMG-C6, cultured on porous tissue culture supports, forms polarized, tight-junction epithelia facilitating bioelectric characterization in Ussing chambers. The SMG-C6 epithelia generated transepithelial resistances of 956+/-84Omega.cm2 and potential differences (PD) of -16.9 +/- 1.5mV (apical surface negative) with a basal short-circuit current (Isc) of 23.9 +/- 1.7 microA/cm2 (n = 69). P2 nucleotide receptor agonists, ATP or UTP, applied apically or basolaterally induced a transient increase in Isc, followed by a sustained decreased below baseline value. The peak DeltaIsc increase was partly sensitive to Cl- and K+ channel inhibitors, DPC, glibenclamide, and tetraethylammonium (TEA) and was completely abolished following Ca2+ chelation with BAPTA or bilateral substitution of gluconate for Cl-. The major component of basal Isc was sensitive to apical Na+ replacement or amiloride (half-maximal inhibitory concentration 392 nM). Following pretreatment with amiloride, ATP induced a significantly greater Isc; however, the poststimulatory decline was abolished, suggesting an ATP-induced inhibition of amiloride-sensitive Na+ transport. Consistent with the ion transport properties found in Ussing chambers, SMG-C6 cells express the rat epithelial Na+ channel alpha-subunit (alpha-rENaC). Thus, cultured SMG-C6 cells produce tight polarized epithelia on permeable support with stimulated Cl- secretory conductance and an inward Isc accounted for by amiloride-sensitive Na+ absorption.

Ion transport in an immortalized rat submandibular cell line SMG-C6

The immortalized rat submandibular epithelial cell line, SMG-C6, cultured on porous tissue culture supports, forms polarized, tight-junction epithelia facilitating bioelectric characterization in Ussing chambers. The SMG-C6 epithelia generated transepithelial resistances of 956+/-84Omega.cm2 and potential differences (PD) of -16.9 +/- 1.5mV (apical surface negative) with a basal short-circuit current (Isc) of 23.9 +/- 1.7 microA/cm2 (n = 69). P2 nucleotide receptor agonists, ATP or UTP, applied apically or basolaterally induced a transient increase in Isc, followed by a sustained decreased below baseline value. The peak DeltaIsc increase was partly sensitive to Cl- and K+ channel inhibitors, DPC, glibenclamide, and tetraethylammonium (TEA) and was completely abolished following Ca2+ chelation with BAPTA or bilateral substitution of gluconate for Cl-. The major component of basal Isc was sensitive to apical Na+ replacement or amiloride (half-maximal inhibitory concentration 392 nM). Following pretreatment with amiloride, ATP induced a significantly greater Isc; however, the poststimulatory decline was abolished, suggesting an ATP-induced inhibition of amiloride-sensitive Na+ transport. Consistent with the ion transport properties found in Ussing chambers, SMG-C6 cells express the rat epithelial Na+ channel alpha-subunit (alpha-rENaC). Thus, cultured SMG-C6 cells produce tight polarized epithelia on permeable support with stimulated Cl- secretory conductance and an inward Isc accounted for by amiloride-sensitive Na+ absorption.

Effects of low concentrations of paraoxon on Ca(2+) mobilization in a human parotid salivary cell-line HSY

The salivary gland is a target organ of organophosphate pesticides (OPs). Inhibition of acetylcholinesterase (AChE) by OPs leads to a decrease in acetylcholine (ACh) breakdown that results in overstimulation of muscarinic cholinergic receptors (mChR). However, OPs may also directly interact with downstream elements of the phosphoinositide (PI) signalling pathway coupled with mChR. The present study examined the effects of exposure to low concentrations of the OP paraoxon on inositol 1,4,5-trisphosphate (IP(3)) formation and Ca(2+) mobilization in response to ACh or ATP in the human parotid cell-line HSY. Exposure to 0.1 and 1 nM, but not 10 nM, paraoxon for 24 hr significantly elevated the basal cytosolic free Ca(2+) ([Ca(2+)](i)). This increase was abolished by atropine. Ca(2+) release from the IP(3)-sensitive store in response to ACh or ATP, a P2Y-nucleotide agonist, was significantly increased in cells pre-exposed to 0.1 nM paraoxon. However, IP(3) formation was inhibited by paraoxon but mChR expression was not altered. Although IP(3) receptor expression was not changed, Ca(2+) release elicited by IP(3) in streptolysin O toxin-permeabilized cells was significantly larger in cells pre-exposed to 0.1 nM paraoxon, suggesting that paraoxon increases the sensitivity of IP(3) receptors. Paraoxon exposure also induced a concentration-dependent reduction in the total capacity of intracellular Ca(2+) stores, whereas the capacity of the IP(3)-sensitive Ca(2+) store was not altered by paraoxon, as judged by discharging of the IP(3)-sensitive Ca(2+) store with thapsigargin (TG). Ca(2+) influx stimulated by ACh or ATP was also enhanced by 0.1 nM, but not 1 and 10 nM, paraoxon. On the other hand, Ca(2+) influx activated by TG was enhanced by exposure to all concentrations of paraoxon, indicating that paraoxon modulates the Ca(2+) entry pathway. These results suggest that low concentrations of paraoxon interact with elements of the PI pathway, enhancing Ca(2+) release and influx mechanisms.

Regulation of (1-3)-beta-glucan-stimulated Ca(2+) influx by protein kinase C in NR8383 alveolar macrophages

Stimulation of (1-3)-beta-glucan receptors results in Ca(2+) influx through receptor-operated channels in alveolar macrophages (AMs), but the mechanism(s) regulating Ca(2+) influx is still undefined. In this study we investigated the role of protein kinase C (PKC) regulation of Ca(2+) influx in the NR8383 AM cell line using the particulate (1-3)-beta-glucan receptor agonist zymosan. PKC inhibition with calphostin C (CC) or bisindolymaleimide I (BSM) significantly reduced zymosan-induced Ca(2+) influx, whereas activation of PKC with phorbol-12-myristate 13-acetate (PMA) or 1, 2-dioctanoyl-sn-glycerol (DOG) mimicked zymosan, inducing a concentration-dependent Ca(2+) influx. This influx was dependent on extracellular Ca(2+) and inhibited by the receptor-operated Ca(2+) channel blocker SK&F96365, indicating that zymosan and PKC activate Ca(2+) influx through a similar pathway. NR8383 AMs expressed one new PKC isoform (delta) and two atypical PKC isoforms (iota and lambda), but conventional PKC isoforms were not present. Stimulation with zymosan resulted in a translocation of PKC-delta from the cytosol to the membrane fraction. Furthermore, inhibition of protein tyrosine kinases (PTKs) with genistein prevented zymosan-stimulated Ca(2+) influx and PKC-delta translocation. These results suggest that PKC-delta plays a critical role in regulating (1-3)-beta-glucan receptor activated Ca(2+) influx in NR8383 AMs and PKC-delta translocation is possibly dependent on PTK activity.

Changes in calcium concentrations in subcellular compartments of rat submandibular gland acinar cells induced by cholinergic stimulation

The effects of cholinergic and alpha-adrenergic stimulation on calcium concentrations in rat submandibular gland acinar cells were evaluated at the subcellular level by electron probe X-ray microanalysis, and the subcellular distribution of receptors for inositol 1,4,5-trisphosphate (IP(3)Rs) was investigated by electron microscopic immunohistochemistry. For measurement of calcium concentrations, experiments were carried out both in vivo and in vitro. In in vivo experiments, fragments of glands were removed and slam-frozen 3 min after intraperitoneal injection of an agonist. In in vitro experiments, the gland tissue was enzymatically dispersed, treated with an agonist in the presence or absence of extracellular Ca(2+), and slam-frozen. The frozen specimens were cut into ultrathin cryosections, which were then freeze dried. Spectra were collected from secretory granules, the perinuclear cytoplasm containing endoplasmic reticulum (ER), and the nucleus of the acinar cells. A clear decrease in calcium content in secretory granules was observed after cholinergic stimulation both in vivo and in vitro in the presence or absence of extracellular Ca(2+). In the presence of extracellular Ca(2+), cholinergic stimulation following alpha-adrenergic stimulation reduced the calcium content in secretory granules to the same extent as cholinergic stimulation alone. No significant changes in the calcium content of the perinuclear cytoplasm and the nucleus were noticed after cholinergic stimulation. alpha-adrenergic stimulation did not significantly affect the calcium concentrations in any of the three compartments studied. IP(3)Rs were localized to ER lamellae, but not to secretory granule membranes or to nuclear membranes. Our findings suggest that: (1) in rat submandibular acini, Ca(2+) can be released from secretory granules by exposure to cholinergic, but not alpha-adrenergic, stimuli, (2) there are, however, no IP(3)Rs present in the granular membrane and the trigger for the Ca(2+) release remains under study, and (3) the response to either type of stimulus does not involve changes in the Ca(2+) content of the nucleus or of the perinuclear cytoplasm/ER, despite the presence of IP(3)Rs in the latter structure. This may be the result of limitation in the technique used, which cannot measure changes in the proper compartment of the ER.

Effects of forksolin, dibutyryl cAMP and H89 on Ca2+ mobilization in submandibular salivary cells of newborn rats

The effects of substances which affect cAMP or the cAMP-dependent protein kinase (PKA) on the inositol 1,4,5-trisphosphate (IP3) and Ca2+ responses to acetylcholine or thapsigargin were investigated in submandibular gland cells of newborn rats. Exposure to forskolin, dibutyryl cAMP or the PKA inhibitor H89 did not affect the formation of IP3 or the release of Ca2+ from intracellular stores elicited by acetylcholine. However, the thapsigargin-induced Ca2+ release was reduced by dibutyryl cAMP and enhanced by H89 in immature cells. Ca2+ influx activated by acetylcholine and thapsigargin was additive in immature cells but not in mature cells, suggesting the presence of a separate Ca2+ entry pathway in immature cells. Moreover, the acetylcholine-stimulated Ca2+ influx was significantly potentiated by forskolin and dibutyrylcAMP, but not by H89 in immature cells. In contrast, the thapsigargin-activated Ca2+ influx was dramatically enhanced by H89, but not by forskolin and dibutyrylcAMP in these cells. This modulation of Ca2+ mobilization by the test substances is different from that observed in mature submandibular cells in which forskolin, dibutyrylcAMP and H89 affected both IP3 formation and Ca2+ release in response to acetylcholine. Therefore, these results suggest differences in the interaction between the cAMP-PKA and the phosphoinositide-Ca2+ signalling pathways of mature and immature salivary cells. The modulation of Ca2+ influx by the cAMP-PKA pathway in immature cells is likely to play a part in the maturation of salivary cells.

Modulation of Ca2+ mobilization by protein kinase C in the submandibular duct cell line A253

The expression of protein kinase C (PKC) isoforms and the modulation of Ca2+ mobilization by PKC were investigated in the human submandibular duct cell line A253. Three new PKC (nPKC) isoforms (delta, epsilon, and theta) and one atypical PKC (aPKC) isoform (lambda) are expressed in this cell line. No classical PKC (cPKC) isoforms were present. The effects of the PKC activator phorbol 12-myristate-13-acetate (PMA) and of the PKC inhibitors calphostin C (CC) and bisindolymaleimide I (BSM) on inositol 1,4,5-trisphosphate (IP3) and Ca2+ responses to ATP and to thapsigargin (TG) were investigated. Pre-exposure to PMA inhibited IP3 formation, Ca2+ release and Ca2+ influx in response to ATP. Pre-exposure to CC or BSM slightly enhanced IP3 formation but inhibited the Ca2+ release and the Ca2+ influx induced by ATP. In contrast, pre-exposure to PMA did not modify the Ca2+ release induced by TG, but reduced the influx of Ca2+ seen in the presence of this Ca2+-ATPase inhibitor. These results suggest that PKC modulates elements of the IP3/Ca2+ signal transduction pathway in A253 cells by (1) inhibiting phosphatidylinositol turnover and altering the sensitivity of the Ca2+ channels to IP3, (2) altering the activity, the sensitivity to inhibitors, or the distribution of the TG-sensitive Ca2+ ATPase, and (3) modulating Ca2+ entry pathways.

Effects of serum on calcium mobilization in the submandibular cell line A253

The effects of serum on inositol 1,4,5-trisphosphate (IP3) formation and Ca2+ mobilization in the human submandibular cell line A253 were studied. Exposure of A253 cells to fetal bovine serum (FBS) elicited a 3.3-fold increase in IP3 formation and a concentration-dependent transient increase in cytosolic free Ca2+ concentration ([Ca2+]i), which was similar in Ca2+-containing and Ca2+-free media. Newborn bovine serum (NBS), but not bovine serum albumin (BSA), induced a similar response. The Ca2+ release triggered by FBS was significantly (88%) reduced by the phospholipase C inhibitor U73122, indicating that Ca2+ release induced by FBS is through the PLC pathway. Pretreatment with the tyrosine kinase inhibitor genistein abolished the FBS- and NBS-induced Ca2+ release, suggesting that tyrosine kinase plays an important role in mediating the Ca2+ release. Pre-exposure to ATP or thapsigargin (TG) significantly reduced the FBS-induced [Ca2+]i increase, indicating that Ca2+ release caused by FBS is from the TG- or ATP-sensitive Ca2+ store. While FBS exposure elicited a large Ca2+ release, it reduced Ca2+ influx. Furthermore, FBS significantly inhibited the Ca2+ influx activated by the depletion of intracellular stores by ATP or TG. These results suggest that (1) serum elicits Ca2+ release from ATP- and TG-sensitive stores, which is mediated by IP3; (2) the serum-induced Ca2+ release may be modulated by a tyrosine kinase-associated process; and (3) serum strongly inhibits Ca2+ influxes including the store depletion-activated Ca2+ influx.

Inhibition of Ca2+ influx by pentoxifylline in NR8383 alveolar macrophages

Pentoxifylline (PTF), a phosphodiesterase (PDE) inhibitor, can prevent inflammation and tissue damage in animal and in vitro human studies. However, the underlying mechanism remains unclear. Since Ca2+ is a critical signal regulating the release of inflammatory mediators in macrophages, the effects of PTF on Ca2+ influx were examined in NR8383 alveolar macrophages (AMs). PTF induced a dose-dependent inhibition on Ca2+ influx activated by zymosan and by protein kinase C (PKC) activators 1,2-dioctanoyl-sn-glycerol (DOG) or phorbol-12-myristate 13-acetate (PMA). The inhibition appeared to be specifically on the receptor-operated Ca2+ entry. The capacitative Ca2+ entry was not affected by PTF. The inhibition was not due to altered cAMP levels since the zymosan-activated Ca2+ influx was not affected by the adenylate cyclase activator forskolin, nor by dibutyryl cAMP. Pretreatment with protein tyrosine kinase (PTK) inhibitor genistein abolished zymosan-induced, but not DOG-induced Ca2+ influx, suggesting that PTK is an upstream element of the signaling cascade and not the target of PTF. The Ca2+ entry activated by zymosan and by PKC activators was inhibited by the mitogen-activated protein kinase (MAPK) inhibitor PD98059. Moreover, activation of MAPK by C6-ceramide (C6C) triggered a similar Ca2+ influx as elicited by zymosan and PKC activators, suggesting that MAPK is an element of the pathway. The C6C-induced Ca2+ influx was also inhibited by PTF. These results indicate that PTF blocks the receptor-operated Ca2+ influx in NR8383 AMs by inhibiting PDE which may acts as a downstream element of the signaling pathway or by direct interaction with Ca2+ channels.

Modulation of Ca2+ mobilization by protein kinase C in rat submandibular acinar cells

The effects of protein kinase C (PKC) activation and inhibition on the inositol 1,4,5-trisphosphate (IP3) and cytosolic Ca2+ ([Ca2+]i) responses of rat submandibular acinar cells were investigated. IP3 formation in response to acetylcholine (ACh) was not affected by the PKC activator phorbol 12-myristate 13-acetate (PMA), nor by the PKC inhibitor calphostin C (CaC). The ACh-elicited initial increase in [Ca2+]i in the absence of extracellular Ca2+ was not changed by short-term (0.5 min) exposure to PMA, but significantly reduced by long-term (30 min) exposure to PMA, and also by pre-exposure to the PKC inhibitors CaC and chelerythrine chloride (ChC). After ACh stimulation, subsequent exposure to ionomycin caused a significantly (258%) larger [Ca2+]i increase in CaC-treated cells than in control cells. However, pre-exposure to CaC for 30 min did not alter the Ca2+ release induced by ionomycin alone. These results suggest that the reduction of the initial [Ca2+]i increase is due to an inhibition of the Ca2+ release mechanism and not to store shrinkage. The thapsigargin (TG)-induced increase in [Ca2+]i was significantly reduced by short-term (0.5 min), but not by long-term (30 min) exposure to PMA, nor by pre-exposure to ChC or CaC. Subsequent exposure to ionomycin after TG resulted in a significantly (70%) larger [Ca2+]i increase in PMA-treated cells than in control cells, suggesting that activation of PKC slows down the Ca2+ efflux or passive leak seen in the presence of TG. Taken together, these results indicate that inhibition of PKC reduces the IP3-induced Ca2+ release and activation of PKC reduces the Ca2+ efflux seen after inhibition of the endoplasmic Ca2+-ATPase in submandibular acinar cells.

Cross-talk in signal transduction pathways of rat submandibular acinar cells

The effects of cyclic AMP-generating substances and of the cAMP-dependent protein kinase (PKA) inhibitor H89 on the inositol 1,4,5-trisphosphate (IP3) and Ca2+ responses to acetylcholine (ACh) were examined in rat submandibular acini. Pre-exposure to forskolin (5 microM) and to dibutyryl cyclic AMP (db-cAMP, 1 mM) increased the IP3 formation in response to ACh while H89 reduced it. The enhancement of the IP3 response was not seen, however, in cells pre-exposed to isoproterenol (10 microM) for 45 min. Despite the increase in IP3 formation, pre-exposure to forskolin or db-cAMP inhibited the release of Ca2+ induced by ACh in cells incubated in Ca2+-free solutions. H89 had no effect on the ACh-generated Ca2+ signal. Manipulation of PKA had no effect on the release of Ca2+ induced by thapsigargin. Pre-exposure to test substances caused changes in the rate of Ca2+ influx which paralleled those in Ca2+ release. It is concluded that PKA interacts with IP3/Ca2+-mediated signaling in submandibular cells at two levels, IP3 generation and Ca2+ release from IP3-sensitive stores. Through phosphorylation of target elements, PKA modifies the coupling of the muscarinic receptor with membrane phosphoinositides and the sensitivity of endoplasmic Ca2+ channels to IP3. The effects on these two components of the IP3/Ca2+ signaling pathway depend, however, on the length of exposure to test substances and on the up- or down-regulation of PKA.

Alterations in Ca2+ storage and mobilization in submandibular acinar cells of reserpine-treated rats

The present study investigated the effects of the catecholamine-depleting drug reserpine on cellular Ca2+ storage and mobilization in rat submandibular acinar cells. Adult rats received seven daily injections of reserpine (0.5 mg/kg) and inositol 1,4,5-trisphosphate (IP3) formation and Ca2+ mobilization were measured in isolated submandibular acinar cells. Ultrastructural analysis demonstrated a significant reduction in rough endoplasmic reticulum (ER) and a dramatic accumulation of secretory granules in the cells of treated animals. Reserpine reduced acetylcholine (ACh)-stimulated IP3 formation by 46% and the initial increase in cytosolic Ca2+ concentration ([Ca2+]i) in response to ACh or thapsigargin was reduced by 21 and 56%, respectively. While norepinephrine (NE) did not induce significant IP3 formation, the [Ca2+]i response to NE was increased 360% by reserpine treatment. Reserpine treatment also enhanced the sustained [Ca2+]i increase following these stimuli. After stimulation with ACh or NE, exposure to ionomycin caused a further elevation in [Ca2+]i which was significantly larger in the cells of treated animals. After exposure to agonist + ionomycin, addition of monensin induced a third increase in [Ca2+]i which was significantly larger in cells of reserpine-treated animals. While capacitative Ca2+ entry was not altered, NE-activated Ca2+ influx was abolished after reserpine treatment. Reserpine treatment therefore alters IP3-sensitive and insensitive Ca2+ stores, non-capacitative Ca2+ influx and active Ca2+ transport in submandibular acinar cells of rats.

Effects of particulate and soluble (1-3)-beta-glucans on Ca2+ influx in NR8383 alveolar macrophages

Particulate and soluble (1-3)-beta-glucans are effective in preventing infections by enhancing macrophage and neutrophil functions. However, the mechanisms triggering these enhanced cellular responses are essentially unknown. We recently demonstrated that zymosan, a particulate (1-3)-beta-glucan receptor agonist, caused an influx of Ca2+ in NR8383 rat alveolar macrophages (AMs) and a resulting increase in intracellular Ca2+ (Zhang et al., J. Leukoc. Biol. 62 (1997) 341-348). Since Ca2+ is important in mediating leukocyte responses, we investigated whether other (1-3)-beta-glucans also alter Ca2+ mobilization in AMs. Particulate and soluble (1-3)-beta-glucans derived from Saccharomyces cerevisiae were used in these studies. Like zymosan, particulate (1-3)-beta-glucan (WGPs) caused a concentration-dependent increase in [Ca2+]i, which was inhibited by removal of extracellular Ca2+ and by SKF96365, an inhibitor of receptor-operated Ca2+ channels. When three different soluble (1-3)-beta-glucans, with molecular weights of approximately 11,000, 150,000, and 1,000,000 Da, were tested alone for effects on Ca2+ responses, the low molecular weight (1-3)-beta-glucan produced no effect and the intermediate and high molecular weight (1-3)-beta-glucans caused only a small increase in [Ca2+]i. Interestingly, however, all three soluble (1-3)-beta-glucans could significantly reduce the Ca2+ responses induced by a subsequent exposure to either WGPs or zymosan. These results demonstrate that: 1) particulate (1-3)-beta-glucan activates Ca2+ influx in NR8383 macrophages through receptor-operated Ca2+ channels; 2) soluble (1-3)-beta-glucans do not strongly activate Ca2+ influx in these cells; and 3) soluble (1-3)-beta-glucans significantly inhibit Ca2+ influx induced by WGPs or zymosan. Soluble (1-3)-beta-glucans are likely to prevent Ca2+ influx by competitively binding to the (1-3)-beta-glucan receptors recognizing zymosan and WGPs. The smaller Ca2+ influx induced by soluble (1-3)-beta-glucans may represent only a partial activation of post-receptor signal transduction pathways necessary for inducing Ca2+ influx.

Characterization of Ca2+ mobilization in the human submandibular duct cell line A253

The regulation of Ca2+ mobilization in the human submandibular duct cell line A253 was investigated by monitoring cytosolic free Ca2+ concentrations ([Ca2+]i) using the Ca(2+)-sensitive fluorescent indicator fura-2 and by measuring inositol 1,4,5-triphosphate (IP3) formation. An increase in [Ca2+]i was elicited by ATP, isoproterenol (IPR), or vasoactive intestinal polypeptide (VIP), but not by acetylcholine, norepinephrine, or substance P, suggesting that Ca2+ mobilization is regulated by P2-purinergic, beta 2-adrenergic, and VIP receptors. 1,4,5-IP3 formation was significantly increased by ATP but not by the other agonists. Exposure of the cells to a membrane permeable cAMP analog, dibutyryl-cAMP, or to the adenylate cyclase activator forskolin induced a smaller increase in [Ca2+]i, indicating that the IPR-induced Ca2+ release is not mediated by cyclic AMP. Inhibition of the endoplasmic Ca(2+)-ATPase with thapsigargin (TG) in Ca(2+)-free medium induced a 207% increase in [Ca2+]i, and a subsequent exposure to ATP caused a further increase in [Ca2+]i of 104%. Similarly, TG exposure after ATP induced a further Ca2+ release, suggesting that the TG-sensitive store and the IP3-sensitive store do not overlap. Similar results were observed by sequential exposure to TG and IPR or to ATP and IPR. Ca2+ influx across the plasma membrane was enhanced after ATP or TG, but not after IPR. Our findings show a unique pattern of Ca2+ mobilization in the A253 cell line: (i) Ca2+ mobilization is regulated by P2-purinergic, beta 2-adrenergic, and VIP receptors; (ii) Ca2+ release is mediated by 1,4,5-IP3 and probably by an unknown mediator; (iii) TG, P2-, and beta 2-agonists discharge separate Ca2+ stores; and (iv) ATP and TG, but not IPR, regulate Ca2+ influx.

Regulation of cytosolic free Ca2+ in cultured rat alveolar macrophages (NR8383)

Ca2+ mobilization in the rat alveolar macrophage cell line NR8383 was examined with the Ca2+-sensitive fluorescent probe Fura-2. ATP and norepinephrine elicited a 108 and 46% increase, respectively, in cytosolic free Ca2+ concentration ([Ca2+]i). Acetylcholine, nicotine, isoproterenol, substance P, and vasoactive intestinal polypeptide did not alter [Ca2+]i. Inositol 1,4,5-trisphosphate (IP3) formation was also activated by ATP. The carbohydrate-rich cell wall preparation, zymosan, induced a gradual [Ca2+]i, increase only in the presence of external Ca2+, but did not activate IP3 formation. This increase was abolished by laminarin and by removal of extracellular Ca2+, suggesting that the [Ca2+]i increase was activated by beta-glucan receptors and mediated by Ca2+ influx. This influx was significantly reduced by SKF96365, but not by nifedipine, (omega-conotoxin GVIA, (omega-agatoxin IVA, or flunarizine. These results suggest that release of intracellular Ca2+ in NR8383 cells is regulated by P2-purinoceptors and that zymosan causes Ca2+ influx via a receptor-operated pathway.

Comparison of calcium mobilization in response to noradrenaline and acetylcholine in submandibular cells of newborn and adult rats

The response of mature and immature rat submandibular cells to alpha-receptor stimulation was compared in terms of the generation of inositol triphosphate (IP3) and Ca2+ mobilization, and of how the calcium mobilization response affects acetycholine (ACh)-induced Ca2+ mobilization. In mature cells, noradrenaline (NA) caused much smaller IP3 and Ca2+ responses than ACh. However, the Ca2+ release induced by NA was enough to partially discharge an agonist-sensitive store and to reduce Ca2+ release by a subsequent ACh stimulus. Exposure to NA also caused an influx of Ca2+ in the mature cells, which was largely associated with Ca2+ entry induced by store depletion (i.e. capacitative entry). In the immature submandibular cells of newborn rats, NA caused essentially no IP3 response and a small Ca2+ release, which only partially affected the Ca2+ released by a subsequent exposure to ACh. In contrast to adult cells, immature cells did not show an increased Ca2+ influx after exposure to NA. However, prestimulation with this agonist potentiated the Ca2+ influx activated by ACh in the cells of newborn rats, but not in cells of adult rats. As both mature and immature submandibular cells have a well-developed phosphoinositide turnover response to ACh, the findings in mature cells suggest a less efficient coupling between alpha-receptors and phospholipase C, while those in immature cells suggest that this coupling is even less functional in the early stages of postnatal development. In permeabilized and 45Ca(2+)-loaded mature cells, cyclic ADP-ribose (cADPR) released 13.4% of loaded 45Ca2+ and this release was significantly reduced by pre-exposure to IP3. Similarly, pre-exposure to cADPR also reduced the IP3-induced 45Ca2+ release. It is concluded that: (1) stimulation with NA induces a smaller Ca2+ release in mature and immature submandibular cells than ACh; (2) the mediator for this small Ca2+ mobilization may be cADPR; and (3) NA stimulates capacitative Ca2+ entry in mature cells, but not in immature cells, and it also activates a Ca2+ entry pathway distinct from the one induced by store depletion, particularly in immature cells.

Effects of cholinergic and alpha-adrenergic agonists on the monovalent ion content of rat submandibular gland acinar cells studied by X-ray microanalysis

The effects of cholinergic and alpha-adrenergic stimulation (in vivo and in vitro) on the monovalent ion content of rat submandibular gland acinar cells were evaluated at the subcellular level by X-ray microanalysis. Fragments of glands or enzymatically dispersed acini were slam-frozen and cut into ultrathin cryosections. Spectra were collected from secretory granules, nucleus, the basal cytoplasm containing endoplasmic reticulum and the apical cytoplasm identified between secretory granules. No significant changes in Na and Cl content were observed after the isolation of acini, but the K concentration decreased compared with cells from in situ glands. The Cl and K content in all four compartments studied decreased significantly after cholinergic stimulation both in vivo and in vitro but in a more restricted fashion after alpha-adrenergic stimulation. Our findings indicate that: (1) the physiological mechanisms regulating the monovalent ion composition of submandibular cells are relatively well preserved in isolated acinar cells; (2) the results from in vivo experiments are in good agreement with those from in vitro experiments; and (3) the effects of cholinergic and alpha-adrenergic stimulation on the K+ and Cl- efflux at the subcellular level are similar but the response is generally less with alpha-adrenergic stimulation.

The effect of paclitaxel on the progression of polycystic kidney disease in rodents

Woo et al (Nature 368:750-753) reported that parenteral administration of paclitaxel arrested the striking renal enlargement and prolonged life in C57BL/6J-cpk/cpk mice with a rapidly progressive form of polycystic kidney disease (PKD). In the current study, we sought to determine whether paclitaxel could alter the progression of other forms of hereditary PKD in rodents. Paclitaxel was administered by intraperitoneal injection to C57BL/6J-cpk/cpk mice and Han:SPRD-Cy/Cy rats with rapidly progressive PKD and to DBA/2FG-pcy/pcy mice and Han:SPRD-Cy/+ rats with slowly progressive PKD. Paclitaxel (150 micrograms/wk) prolonged the survival of cpk/cpk mice from 24.5 days to more than 65 days and decreased kidney weight relative to body weight from 16.5% at 21 days of age to 8.2% at more than 65 days of age. Mortality attributable to paclitaxel was 12%. By contrast, the administration of paclitaxel (0.1 to 15 mg/kg/wk) to 7- to 10-day-old Han:SPRD-Cy/Cy rats with rapidly progressive PKD had no effect on the course of the disease; moreover, paclitaxel caused severe side effects and premature death in all the Cy/Cy animals. Heterozygous male Cy/+ rats develop slowly progressive renal enlargement and azotemia. Paclitaxel, administered at 7, 15, or 27 mg/kg/wk to male Cy/+ rats from 4 until 10 weeks of age, reduced body weight gain, had an inconsistent effect on kidney weight relative to body weight, and had no effect on the serum urea nitrogen concentration. Mortality associated with the 7, 15, and 27 mg/kg/wk doses of paclitaxel was 0%, 15.4%, and 28.5%, respectively. DBA/2FG-pcy/pcy mice of either sex developed slowly progressive renal enlargement and azotemia. The administration of paclitaxel (100 to 150 micrograms/wk) from 2 to 10 weeks of age to DBA/2FG-pcy/pcy mice with cystic disease had no effect on the increase in kidney weight or on the level of serum urea nitrogen in comparison to untreated cystic animals. Mortality associated with 100- and 150-micrograms/wk doses of paclitaxel was 0% and 20%, respectively. We conclude that paclitaxel diminished the rate of renal enlargement and increased the life span of cpk/cpk mice but not Cy/Cy rats with rapidly progressive forms of PKD. Paclitaxel had no apparent benefit in Cy/+ rats nor pcy/pcy mice with slowly progressive PKD. On the basis of these studies in rodents, it appears that paclitaxel has limited potential usefulness as a therapeutic agent in the treatment of PKD.

Differences in intracellular CA2+ stores of submandibular cells of adult and newborn rats

The intracellular Ca2+ stores of submandibular acinar cells of adult and newborn rats were compared by measuring changes in cytosolic Ca2+ ([Ca2+]i) with the Ca2+-sensitive fluorescent probe, fura-2, in intact cells and 45Ca2+ release in permeabilized cells. In cells of adult rats, acetylcholine (ACh) and thapsigargin (TG) elicited, respectively, a 105% and 125% net increase in [Ca2+]i in Ca2+-free medium. In cells of newborn animals, the ACh-induced [Ca2+]i increase (218%) was larger; but the TG-induced increase was significantly smaller (77%), suggesting that the TG-sensitive Ca2+ pump of the store is less developed, abundant, or responsive in these cells. After ACh or TG, ionomycin elicited a further Ca2+ release. Ionomycin by itself completely discharged the ACh- and TG-sensitive store in cells of mature glands but not in cells of immature glands, suggesting a further difference in the distribution of the agonist and ionomycin sensitivities in the two types of cells. After exposure to ACh + ionomycin or TG + ionomycin, collapsing the intracellular pH gradient with monensin caused a third and large Ca2+ release (262% and 289%, respectively) in cells of adult rats, but a significantly smaller release (96%, P < 0.001, and 57%, P < 0.001, respectively) in cells of newborn rats, suggesting that a third, IP3-insensitive acidic store is significantly smaller in cells of immature glands. In permeabilized and 45Ca2+-loaded cells, inositol-1,4,5-trisphosphate (IP3, 5 microM) induced an identical 45Ca2+ release (34% and 33%, respectively) in both types of cells, but TG induced a significant smaller 45Ca2+ release in cells of immature glands (15%) than in cells of mature glands (33%). Monensin discharged <10% of loaded 45Ca2+ in both types of cells, indicating that the radiotracer was not loaded into the monensin-sensitive store. These results suggest that in cells of immature glands: (1) the TG-sensitive Ca2+ pump of the IP3-sensitive store is not well developed; (ii) the IP3-sensitive store is not completely discharged by ionomycin; and (iii) an acidic store likely to be associated with secretory granules is also underdeveloped and of a smaller size than in cells of mature glands.

Evidence for a Ca2+ pool associated with secretory granules in rat submandibular acinar cells

Intracellular Ca2+ stores in rat submandibular acinar cells were characterized using the Ca(2+)-sensitive fluorescent indicator fura 2 and the radiotracer 45Ca2+. Acetylcholine induced a rapid Ca2+ release from a store sensitive to inositol 1,4,5-trisphosphate (IP3) and to thapsigargin (TG). After this store was presumably depleted, ionomycin caused a further increase in cytosolic free Ca2+ concentration ([Ca2+]i), suggesting the presence of an IP3-insensitive Ca2+ release from a store that is more extensive and heterogeneous than the IP3-sensitive one and includes a small mitochondrial component. After both of these stores had been discharged, exposure to monensin caused an additional release of Ca2+ from a third store. This store appears to be associated with secretory granules, since Ca2+ release was significantly reduced when degranulation was induced by isoprenaline. This third store appears to be insensitive to IP3, discharges Ca2+ when the pH gradient across the limiting membrane is collapsed with monensin and only in the presence of both ionomycin and monensin. Ca2+ release from this store is not by Na+/Ca2+ exchange, since simply altering [Na+]i did not cause significant Ca2+ release. In permeabilized cells, IP3 and TG released approx. 35% of 45Ca2+, and ionomycin released an additional 57%, whereas monensin only caused a small additional release, suggesting that only IP3- and ionomycin-sensitive stores are loaded with 45Ca2+ under these conditions. The absence of significant isotope uptake into the ionomycin+monensin-sensitive store may result from a low rate of tracer accumulation or from the lack of Ca2+ pumps in the store. The pattern of response was similar in the presence and absence of mitochondrial inhibitors, indicating that the store is not located in mitochondria. In summary, these results suggest that a substantial IP3-insensitive Ca2+ store is present in secretory granules in rat submandibular acinar cells.

Absence of acetylcholine- and ionomycin-activated Cl- currents in submandibular cells of early postnatal rats

Using the whole-cell patch-clamp technique, we investigated developmental changes in the expression of an acetylcholine- (Ach-) activated Cl- conductance in rat submandibular acinar cells. ACh induced an oscillatory inward current in cells isolated from animals older than 5 weeks, but not in animals less than 2-3 weeks of age. The current/voltage (I/V) relationship of the ACh-induced current was that of an outward rectifier, and the current was inhibited by intracellular BAPTA, a Ca2+ buffer, indicating the current was Ca2+ activated. The ACh-induced current was also blocked in the presence of DPC and SITS, two Cl- current inhibitors in other tissues. Ionomycin mimicked the effect of ACh but in a nonoscillatory fashion. The appearance of the ionomycin-induced currents was also age related, as the current was not observed to occur in animals less than 2-3 weeks old. Since both ACh and ionomycin significantly increase cytosolic [Ca2+] in the acinar cells of young animals, the correlation between the age dependence of the ACh-activated Cl- current and the ionomycin-activated Cl- current responses suggests that the lack of responsiveness observed in the young animals is due to the absence of Ca2+-activated Cl- channels, rather than to a deficiency of a cellular mediator.

Evidence for reduced capacity for Ca2+ removal from the cytosol in submandibular cells of newborn rats

The increase in cytosolic free Ca2+ concentration ([Ca2+]i) seen in submandibular cells of early postnatal rats following exposure to acetylcholine (ACh) is larger than in cells of adult rats. To elucidate possible reasons for this difference, we compared Ca2+ movements through Ca2+ pumps in both types of cells using Ca(2+)-sensitive fluorescent probe fura-2 and the radiotracer 45Ca2+. Ca2+ release induced by endoplasmic reticulum (ER) Ca(2+)-pump inhibitor thapsigargin (TG) was significantly smaller in neonatal cells than in adult cells, whereas the inositol 1,4,5-trisphosphate (IP3)-elicited Ca2+ release was comparable in both cell types. This suggests that although the size of the IP3-sensitive Ca2+ pool is adequate in immature cells, the activity of TG-sensitive Ca2+ pump in this pool is lower. The activity of the plasma membrane (PM) Ca(2+)-pump, measured by extrusion of 45Ca2+, was also significantly lower in immature cells. These results indicate that both ER and PM Ca2+ pumps may be functionally underdeveloped in immature cells, and that the enhanced increase of [Ca2+]i seen in response to ACh in immature cells may be partially, if not completely, due to a reduced capacity for removal of Ca2+ from the cytosol by active mechanisms.

G-protein coupling of muscarinic receptors in adult and neonatal rat submandibular cells

The submandibular glands of neonatal and adult rats express muscarinic cholinergic receptors. Receptor occupancy initiates signaling through activation of phospholipase C, hydrolysis of inositol phospholipids, and calcium mobilization. The increased cytoplasmic [Ca2+] activates ion transport pathways, resulting in secretion of primary saliva. We have previously shown that muscarinic receptors are present in the gland of neonates and that they couple effectively to inositol trisphosphate production and Ca2+ mobilization but that the monovalent ion transport paths are poorly activated. To characterize age-related differences in signal transduction further, we examined the coupling of muscarinic receptors to G-proteins by determining the effect of GTP on the IC50 for competition by the muscarinic agonist carbachol with the radiolabeled antagonist, 3H-quinuclidinyl benzylate. Data were fit to one-site and two-site models, and in all cases the two-site model provided the better fit. Using the two-site model, a substantial GTP-induced shift from high affinity to low affinity binding was observed in membranes from adults, whereas more of the receptors were already in the low affinity form in the membranes from neonates, and little additional shift was induced by GTP. These results suggest differences in the G-protein coupling of muscarinic receptors in submandibular cells of adult and early postnatal rats that may be associated with differences in the content, affinity, or properties (i.e., posttranslational modifications) of G-proteins as the cells mature.

Chloride secretion in the submandibular gland of adult and early postnatal rats studied by X-ray microanalysis

Submandibular acinar cells of 1-day-old, 7-day-old, and adult rats were analyzed with X-ray microanalysis after stimulation with carbachol for different time periods (2-7 min). In unstimulated animals, marked differences in elemental content between compartments could be observed: secretory granules had a higher Ca and lower P and K content than other cell compartments. Comparison between different age groups showed significant differences for Ca, which increased with age in all compartments; Mg increased with age in the secretory granules and the apical cytoplasm. Only the glands from adult animals showed a significant effect of cholinergic stimulation: a transient decrease in Cl and K. The Cl concentration in the secretory granules decreased to 60% of the control value, which suggests that the granules release Cl upon stimulation. In young animals, no or little change in elemental distribution was observed after stimulation. This may indicate that Cl- secretion mechanisms are much less prominent in young animals. The ultrastructure of submandibular secretory granules depends on the preparation method: condensed and electrondense in freeze-substituted unfixed tissue, decondensed and more translucent in aldehyde-fixed tissue. This may indicate that the granules can transport water, and swell during the process of aldehyde fixation.

Polycystic kidney disease: etiology, pathogenesis, and treatment

Once viewed as hopelessly incurable disorders and the dustbin for careers in academic medicine, the polycystic kidney diseases have emerged as prime targets of pathophysiologic study and palliative and definitive treatment in the era of molecular medicine. Polycystic kidney disease (PKD) may be hereditary or acquired. The major inherited types are autosomal dominant (AD) and autosomal recessive (AR). ADPKD is caused by at least two (and possibly three) genes located on separate chromosomes, while ADPKD-1 is due to a 14 kb transcript in a duplicated region on the short arm of chromosome 16 very near the alpha-globin gene cluster and the gene for one form of tuberous sclerosis. ADPKD-2 has been assigned to the long arm of chromosome 4. ARPKD is due to a mutated gene on both copies of the long arm of chromosome 6. Cysts originate in renal tubules. Proliferation of tubule epithelial cells modulated by endocrine, paracrine, and autocrine factors is a major element in the pathogenesis of renal cystic diseases. In addition, fluid that is abnormally accumulated within the cysts is derived from glomerular filtrate and, to a greater extent, by transepithelial fluid secretion. Abnormal synthesis and degradation of matrix components associated with interstitial inflammation are additional features in the pathogenesis of renal cystic diseases. The ADPKD genotypes are characterized by bilateral kidney cysts, hypertension, hematuria, renal infection, stones, and renal insufficiency. ADPKD is a systemic disorder; cysts appear with decreasing frequency in the kidneys, liver, pancreas, brain, spleen, ovaries, and testis. Cardiac valvular disorders, abdominal and inguinal hernias, and aneurysms of cerebral and coronary arteries and aorta are also associated with ADPKD. Treatment is supportive: dietary regulation of salt and protein intake, control of hypertension and renal stones, and dialysis and transplantation at the end stage. ARPKD is a relatively rare disease that causes clinical symptoms at birth, with significant mortality in the first month of life. The cysts develop primarily in the collecting ducts because of a failure in the maturation process. Early complications include Potter's syndrome; excessive size of the kidneys, causing respiratory dysfunction; hypertension; and renal insufficiency. Hepatic fibrosis is an associated extrarenal problem that results in significant morbidity in young children and adolescents. Treatment includes supportive care, dialysis, and renal transplantation. Acquired cysts (solitary/simple) are commonplace in older persons. Multiple cysts may be seen in association with potassium deficiency, congenital disorders, metabolic diseases, and toxic renal injury.(ABSTRACT TRUNCATED AT 400 WORDS)

Developmental aspects of fluid and electrolyte secretion in salivary glands

The salivary glands of rodents undergo considerable cytodifferentiation after birth and are useful models for the study of functional development, including the mechanisms of fluid and electrolyte secretion. In the rat submandibular gland, secretion of salivary fluid cannot be elicited until approximately 2 weeks of age. The currently accepted model of salivary fluid secretion indicates that this process depends on the activation, on stimulation of cholinergic receptors, of several ion transport systems, resulting in a net transport of osmotically active ions (primarily Cl- and Na+) across the acinar epithelium. This creates the necessary osmotic gradient for the transacinar movement of water. The process is associated with a signal transduction pathway involving the formation of phosphoinositide products (primarily inositol triphosphate or IP3) and the mobilization of Ca2+. The latter regulates monovalent ion conductances (K+, Cl-), which are critical for the secretory process. Immature submandibular glands and cells of early postnatal rats have a lower density of cholinergic receptors and release less K+ and Cl- than mature cells and gradually develop other ion transport systems (such as a Na, K, 2Cl cotransport system) involved in the secretory process. Surprisingly, they form more IP3 and show a larger increase in cytosolic Ca2+ when stimulated with maximal or supramaximal concentrations of agonist. Therefore, they show some interesting dissociations in the signal transduction mechanism that suggest differences in the coupling between receptors and membrane phosphoinositides, between IP3 and IP3-dependent Ca2+ stores, and between the Ca2+ signal and the monovalent ion transport systems which are critical for secretion.

Responses of salivary acinar cells to intracellular alkalinization

Responses of rat submandibular acini to intracellular alkalinization were investigated. Intracellular alkalinization was induced by addition of NH4Cl or methyl amines, or by prepulse with Na butyrate. Only partial recovery occurred following Na butyrate prepulse or methylated amine addition, but full recovery was observed following addition of NH4Cl. The latter recovery was DIDS and dimethylamiloride-insensitive but was inhibited by bumetanide or high [K+] and stimulated in Na(+)-free buffer and by ouabain. Acetylcholine stimulated recovery from NH4Cl- or Na butyrate pre-pulse-induced alkalinization and reduced the extent of alkalinization induced by methylated amines. Acetylcholine-stimulated recovery from NH4Cl-induced alkalinization was mimicked by substance P or ionomycin and was partially Ca(2+)-dependent. This stimulated recovery was bumetanide-insensitive but was partially sensitive to charybdotoxin. Taken together, these data indicate that in unstimulated cells, recovery from alkalinization induced by NH4Cl occurs by bumetanide-sensitive transport of the NH4+ ion, that DIDS-inhibitable anion transport contributes little to this recovery, and that acetylcholine and other Ca(2+)-elevating agents accelerate recovery from NH4Cl-induced alkaline challenge by a mechanism insensitive to bumetanide, DIDS, ouabain, and dimethylamiloride but sensitive to extracellular Ca2+ and to charybdotoxin. Partial recovery from alkaline challenge can also occur in the absence of NH4+ ions, and acetylcholine also stimulates this mode of recovery. Together, these data suggest that these cells have little intrinsic ability to recover from intracellular alkalinization and that the NH4+ ion may be a surrogate for K+ in at least two ion transport pathways.

Muscarinic signaling pathway in submandibular cells of adult and early postnatal rats

Elements of the muscarinic signal transduction pathway were compared in submandibular acinar cells of 1-day-old, 1-week-old, and adult rats after exposure to concentrations of acetylcholine ranging from 0.05 to 10 microM. Formation of inositol trisphosphate (IP3) and intracellular Ca2+ were comparable in cells from the three age groups after exposure to agonist concentrations < 1 microM. At higher agonist concentrations, IP3 generation and peak initial changes in [Ca2+]i were significantly greater in cells of newborn animals. In cells of 1-week-old animals, increased peak [Ca2+]i responses were seen even at low agonist concentrations, although IP3 production was not increased when compared with fully mature cells. Increased initial [Ca2+]i peaks, but comparable subsequent plateau [Ca2+]i values, were seen in the immature cells in both Ca(2+)-containing and Ca(2+)-free solutions. Permeabilized cells of early postnatal animals took up less 45Ca2+ into nonmitochondrial Ca2+ pools in the presence of 1.5 mM ATP and also released less tracer in response to intermediate IP3 concentrations than adult cells. Developing salivary cells thus show differences in important functional linkages of the muscarinic signal transduction pathway, including those between receptor activation and phosphoinositide turnover and between IP3 and release of internally stored Ca2+. Differences in the Ca2+ stores or in their sensitivity to IP3 may account for the latter observation. Immature salivary cells seem to have adequate mechanisms for Ca2+ entry.

Intracellular [Ca2+] and K+ and Cl- efflux responses in submandibular cells of neonatal and adult rats

The effects of graded doses (5 x 10(-8) to 10(-5)) acetylcholine on intracellular Ca2+ and on 86Rb and 36Cl efflux were compared in submandibular cell clusters of 1 and 7 day-old and adult rats. Initial Ca2+ peaks were similar at agonists concentrations lower than 10(-7) M but the release of Rb+ and Cl- were smaller in cells of young animals. At higher agonist concentrations, Ca2+ peaks were higher in immature cells; however, initial Cl- (but not Rb+) efflux was similar to that of mature cells. Plateau Ca2+ levels were independent of age and agonist concentrations but the content of Cl- and Rb+ varied greatly and differences between age groups were less evident. These data confirm a dissociation between intracellular Ca2+ levels and Ca(2+)-mediated ion transport in immature salivary cells.

Effects of NH4Cl and dimethylamine on Cl- fluxes in resting and stimulated rat submandibular acinar cells

Transmembrane movements of K+ and Cl- in salivary acinar cells are important in the formation of saliva, and may be affected by changes in intracellular pH (pHi). Exposure to NH4Cl increases pHi transiently, but NH4+ may have effects independent of pHi. To investigate how Cl- transport may be altered under these conditions, rat submandibular acini were exposed to NH4Cl, and transmembrane Cl- transport was studied with 36Cl-. NH4Cl increased intracellular Cl- in these cells. The initial phase of this increase was partially HCO(3-)-dependent and was inhibited by 1 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), while the sustained phase was inhibited by 0.1 mM bumetanide. NH4Cl also inhibited acetylcholine-induced Cl- efflux from tracer preloaded cells. Changes in pH did not always correlate in time or extent with those of Cl- transport. We conclude that 1) exposure to NH4Cl increases Cl-uptake primarily by a bumetanide-sensitive transport system that did not reach steady state during the experiment, 2) exposure to NH4Cl also stimulates Cl- uptake by a DIDS-sensitive mechanism, and 3) only the latter is pHi sensitive.

Intracellular pH changes induced by exposure to weak acids and bases in submandibular cells of early postnatal rats

The intracellular pH of submandibular cells of adult, 1-day-old and 1-week-old rats was measured with the pH sensitive fluorimetric indicator SNARF-1, following shifts induced by exposure to a weak acid (sodium butyrate) or a weak base (NH4Cl). The effects of several ion transport inhibitors and agonists on both the pH change and the rate of recovery were examined. The results indicate that, in most respects, the processes involved in pH regulation were similar in the neonatal and mature cells. However, cholinergic and peptidergic stimulation accelerated recovery from sodium butyrate-induced acidification more, and from NH4Cl-induced alkalinization less, in cell preparations from 1-day-old animals.

The effect of NH4Cl on Rb+ fluxes in resting and stimulated rat submandibular acinar cells

Dispersed salivary acini isolated from the rat submandibular gland were incubated in a HEPES-buffered Krebs-Ringer solution or in the same buffer containing 20 mM NH4Cl and the accumulation and efflux of K+ were measured with the radiotracer 86Rb+, in the presence and absence of acetylcholine and of transport inhibitors. Exposure to NH4Cl caused a significant (greater than 50%) reduction in tracer accumulation. This effect was blocked by 0.1 mM bumetanide, but not by 1 mM ouabain. The effect of NH4Cl was, on the other hand, nearly additive with that of 1 microM acetylcholine. In cells preincubated with tracer, acute addition of NH4Cl caused a significant net efflux of isotope, so that the tracer content fell to 45% of the control value within 10 min. Bumetanide added to preloaded cells in the same fashion had no effect on tracer content and did not modify the efflux of 86Rb+ induced by 1 microM acetylcholine. However, this inhibitor essentially abolished the NH4Cl-induced tracer efflux. Exposure to NH4Cl during tracer loading did not appear to affect subsequent agonist-stimulated tracer efflux. These results suggest that: (1) the inhibition of K+ entry by NH4Cl is due to an effective competition by the NH4+ ion with Rb+ (and K+) for uptake via a bumetanide-sensitive Na+/K+/2Cl- contransporter.(ABSTRACT TRUNCATED AT 250 WORDS)

Na+ influx mechanisms in submandibular salivary cells of newborn rats

Uptake of this isotopic tracer was essentially the same as in cells derived from salivary glands of adult animals, both in the absence and in the presence of 1 microM acetylcholine, 10 microM monensin or 10 microM A23187. Tracer accumulation in resting cells was inhibited in the immature cells by 1 mM amiloride but the inhibition was significantly smaller than in fully mature cells (16 and 33%, respectively). Bumetanide inhibited tracer uptake by 28% in mature cells not exposed to agonist, but had essentially no effect in those of newborn rats. The tracer content of adult cells exposed to acetylcholine in Ca(2+)-free incubation solutions was significantly reduced when compared to that of cells exposed to agonist in solutions containing 1.0 mM CaCl2. A similar but significantly smaller reduction in tracer content was observed in cells of newborn animals incubated in the Ca(2+)-free medium. The inhibition of 22Na uptake observed in the presence of amiloride was the same in both types of cells in the presence or absence of external Ca2+. The findings suggest that Na entry into immature salivary cells of newborn rats is quantitatively similar to that in mature cells, but that the contribution of the loop diuretic-sensitive co-transporter and of the amiloride-sensitive Na/H exchange to Na+ entry is less in the immature cells. Na entry in the immature cells is likely to occur, therefore, primarily by other mechanisms such as Ca(2+)-regulated channels.

Effects of acetylcholine and monensin on 22Na uptake and cytosolic Ca2+ in rat submandibular salivary cells

Cells isolated by enzymatic digestion of gland fragments were incubated in solutions with or without Ca2+ or Na+ and exposed to monensin (10 microM) or acetylcholine (1 microM). Effects on accumulation of 22Na and on cell Ca2+ (measured with fura-2) were compared. In Ca2(+)-containing medium, accumulation of 22Na was increased by the 2 drugs (23 and 20%, respectively) and their effects were additive. Tracer accumulation was also increased by the ionophore A23187. The effect of monensin was not inhibited by 1 mM amiloride, but partially inhibited by 1 mM furosemide. Acetylcholine caused a rapid increase (peak) in cell Ca2+, followed by a gradual decline, while monensin caused a gradual increase with no initial peak. In Ca2(+)-free medium, acetylcholine failed to enhance 22Na accumulation, but still caused a rapid peak in cell Ca2+, followed by a more rapid decrease to resting levels. Monensin enhanced 22Na uptake 16% and caused a gradual increase in cell Ca2+ in this medium. In a medium with no Na+ but containing 1 mM Ca2+, acetylcholine increased cell Ca2+ but no initial peak was observed; monensin caused a slight decrease in cell Ca2+ and then an increase to resting levels. These results suggest important interactions between Na+ and Ca2+ movements in salivary cells. Ca2+ mobilization may activate Na+ uptake and changes in cell Na+ may, in turn, influence Ca2+ mobilization from cell pools. Some of these interactions may involve a Na/Ca co- or counter-transport system.

Amiloride inhibits 22Na uptake and [3H]QNB binding in rat submandibular cells

Dispersed acini isolated by collagenase digestion of the rat submandibular gland were used to compare the effects of amiloride and furosemide on the uptake of the isotopic tracer 22Na and on the binding of [3H]quinuclidinyl benzylate ([3H]QNB). In mM concentrations, both inhibitors reduced 22Na uptake in resting cells 34 and 25-29%, respectively. Acetylcholine (1 microM) enhanced uptake 23% and this effect was reduced 45% by amiloride and 26% by furosemide. Amiloride inhibited the binding of [3H]QNB to crude membranes prepared from fresh submandibular glands in a dose-dependent fashion (IC50 = 8 x 10(-6) M). Furosemide (3 x 10(-8) to 10(-3) M) did not inhibit radioligand binding. Na influx into resting salivary acini thus appears to occur by both amiloride-sensitive and furosemide-sensitive transport systems. The similar inhibition by furosemide of unstimulated and stimulated uptake of 22Na suggests that acetylcholine does not significantly activate the cotransport system within the time frame (i.e., 2 min) of the experiments. Acetylcholine appears to activate an amiloride-sensitive Na/H antiport, but amiloride blocks cholinergic receptors and may thus affect Na transport by receptor blockade. Other actions of amiloride, such as its ability to penetrate into cells and to act as a weak base which alters intracellular pH, may also contribute to the inhibition of Na entry into salivary cells.

Inhibition of 36Cl uptake by stilbene sulphonic acid derivatives and loop diuretics in rat submandibular salivary acini

Acini were isolated from submandibular glands by enzymatic digestion and incubated in HCO3-containing and HCO3-free [hydroxyethyl-1-piperazine-ethane sulphonic acid (HEPES) buffered] solutions to compare the accumulation of the isotopic tracer 36Cl in the absence and presence of stilbene sulphonic acid derivatives and of loop diuretics. Tracer accumulation was similar in both solutions in the absence of inhibitors and reached 17-19 nmol/mg protein after 5 min of incubation. Exposure to 10(-3) M 4,4'-diisothiocyano-2,2'-stilbene disulphonic acid (DIDS) or to 10(-4) M bumetanide in HCO3-buffered medium resulted in significant reductions in both the initial phase (from 0 to 5 min) and the steady-state phase (5-30 min) of 36Cl accumulation. By contrast, in HCO3-free, HEPES-buffered incubation solution, DIDS was significantly less effective in reducing 36Cl accumulation, while bumetanide was somewhat more effective than in HCO3-buffered medium. At a higher dose (10(-3) M), furosemide was less effective than bumetanide in reducing the steady-state tracer content of the cells in the HCO3-buffered medium (22% versus 35% reduction), although the effects were similar in the initial phase of tracer uptake. Exposure to 10(-4) M 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid (SITS) caused an increase in the steady-state 36Cl content of the acini of 24 +/- 9%. Exposure to bumetanide and DIDS caused an additive reduction of tracer content, while exposure to bumetanide and SITS resulted in a smaller reduction than with bumetanide alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Ca2+ mobilization and Cl efflux in submandibular salivary cells of adult and newborn rats

These cells were isolated by enzymatic digestion from glands of 1-day-old and fully mature rats. The effects of exposure to acetylcholine on cytosolic Ca2+ and Cl efflux were studied by, respectively, spectrofluorimetry of fura-2 and the net efflux of the isotopic tracer 36Cl from preloaded cells. In both types of cells, when incubated in Ca2+-containing solutions, acetylcholine initially caused a rapid, significant increase in cytosolic Ca2+ (from approx. 90 to 480-570 nmol), followed by a slower decrease to a plateau value of 280-290 nmol. The initial peak persisted (315-339 nmol) in Ca2+-free solutions but the cytosolic Ca2+ concentrations decreased rapidly to levels below prestimulation values (30 nmol). 36Cl efflux in tracer preloaded cells incubated in Ca2+-containing medium in the presence of acetylcholine was 18% in cells of new born animals and 35% in adult cells. In Ca2+-free medium, mature cells showed a transient but significant (26%) efflux of 36Cl. Cells of 1-day-old rats did not show a net efflux of 36Cl under these conditions, but subsequent addition of Ca2+ caused a 15% reduction (i.e. efflux) in tracer content. The antagonist 3,4,5-trimethoxybenzoate-8(N,N-dithylamino)octyl ester (TMB 8), which blocks internal Ca2+ release, inhibited both the initial increase in cell Ca2+ in both types of cells and the transient efflux of 36Cl seen in mature cells when incubated in Ca2+-free solutions. At high concentrations (5 mM), LaCl3 inhibited efflux of 36Cl in mature cells but not in those of newborn rats. However, at lower concentrations (0.1 mM), which do not interfere with fluorescence spectra, LaCl3 did not inhibit the effect of acetylcholine on cell Ca2+. These results suggest that Cl efflux in adult submandibular cells is regulated by an increase in cell Ca2+ arising from release of internal Ca2+ and from influx of external Ca2+. Both of these responses are evident in cells of newborn animals but Cl efflux is either decreased or absent. This is likely to be associated with a deficiency in the Cl channels or in the coupling between Ca2+ and the channel substrate through regulatory molecules associated with phosphorylation of the channel protein.

The reserpine-treated rat as an experimental animal model for cystic fibrosis: abnormal Cl transport in pancreatic acinar cells

Pancreatic acini of control and reserpine-treated rats were incubated with the isotopic tracer 36Cl to compare Cl accumulation in the absence and presence of secretagogues and transport inhibitors. Two phases of Cl accumulation were ascertained in resting control cells: an initial rate (0-5 min) and a steady state level (10-30 min) of accumulation. Both phases were enhanced by acetylcholine (1 microM) and caerulein (10 nM), but not by 10 nM vasointestinal peptide or 10 microM forskolin. Exposure to 1 mM DIDS (4,4'-diisothiocyano-2,2'-stilbene disulfonic acid) inhibited both phases of Cl accumulation, whereas exposure to 1 mM amiloride had a delayed effect on the initial rate and reduced the steady state phase in both resting (unstimulated) or acetylcholine-stimulated cells. Furosemide (1 mM) had no effect on Cl accumulation when added to the cells just before tracer, but reduced it when added 10 min before. Neither the initial phase nor the steady state level of Cl accumulation were enhanced by acetylcholine in acini of reserpine-treated rats and the effect of DIDS on the initial phase was smaller than in control cells. Continued exposure to this inhibitor resulted, furthermore, in a significantly larger steady state Cl content. The inhibitory effects of amiloride and of a 10-min preincubation with furosemide were similar to those observed in control cells. These results suggest that Cl accumulates in rat pancreatic acini by way of DIDS-sensitive mechanisms that are activated by Ca2+-mediated, but not by cAMP-mediated, secretagogues. These mechanisms are altered in acini of reserpine-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of alpha-receptor stimulation on Cl transport by rat submandibular acini

Dispersed salivary acini isolated from the rat submandibular gland by enzymatic digestion were used to study the effects of alpha-receptor stimulation on transmembrane transport of 36Cl. In the absence of secretagogue, the tracer accumulated in the cells in a time-dependent manner until a steady-state content of 6.8 +/- 0.1 nmol/mg protein was attained after 3-5 min of incubation. Epinephrine (1 mumol/L) alone did not modify 36Cl accumulation but in the presence of the beta-receptor blocker propranolol (1 mumol/L) caused a significant (21%) reduction in the isotope content of the cells to 5.2 +/- 0.1 nmol/mg protein. In acini pre-loaded with 36Cl for 12 min, 1 mumol/L epinephrine caused a rapid but transient net efflux of tracer, but the isotope content subsequently increased to pre-stimulation levels. In the presence of propranolol, however, the efflux of 36Cl induced by epinephrine was larger and more sustained and was partially inhibited by the K-channel blocker quinidine (1 mmol/L) and significantly by the absence of Ca2+ in the incubation medium. The alpha-agonist phenylephrine (10 mumol/L) also significantly reduced the steady-state 36Cl content of tracer-pre-loaded cells. By contrast, exposure of the acini to epinephrine in the presence of the alpha-receptor blocker phentolamine, or the beta-agonist isoproterenol, increased the tracer content of the cells, whether the drugs were added at time zero or to tracer-pre-loaded cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of isoproterenol on Cl transport in rat submandibular salivary-gland acini

In the absence of the beta-adrenoceptor agonist, isoproterenol, acini accumulated 36Cl in a time-dependent manner until a steady-state content of 7.4 +/- 0.2 nmol/mg protein was attained after 5 min of incubation. In the presence of 10 microM isoproterenol the tracer content increased significantly in the first few minutes (40 per cent after 2 min, 33 per cent after 5 min) but then decreased and was essentially the same as in the absence of agonist after 15 min. This effect was inhibited by 1 mM furosemide but was still observed when the cells were incubated in K-free medium. Exposure of tracer-preloaded cells with steady-state isotope content to 10 microM isoproterenol likewise caused a transient but significant increase in tracer content (32 per cent after 6 min); exposure to 1 microM acetylcholine caused a significant and sustained decrease in tracer content (30 per cent), which was not prevented by pre-incubating the cells for 5 min with isoproterenol. Similar transient increases in tracer content of preloaded cells were observed upon exposure to 10 microM concentrations of forskolin or dibutyryl cAMP. Stimulation of beta-receptors does not therefore cause a net Cl efflux in salivary acini and does not prevent the net efflux induced by stimulation of cholinergic receptors. As this efflux may be via a conductance pathway or channels in the apical membrane, these channels do not seem to be regulated by a beta-receptor-coupled, cAMP-mediated pathway in salivary cells.(ABSTRACT TRUNCATED AT 250 WORDS)