[Intra-arterial combination chemotherapy using both regimen selected by chemosensitivity test and caffeine to increase effect for osteosarcoma in extremity]

We treated three patients with osteosarcoma in extremity with intra-arterial combination chemotherapy using a regimen selected by succinate dehydrogenase inhibition chemosensitivity test, and used caffeine to enhance its effect. In two patients with osteosarcoma in distal diametaphysis of the radius and extraskeletal osteosarcoma in sole of the foot, the effect of intra-arterial combination chemotherapy was increased and followed by the functional limb salvage procedure. But in one patient with osteosarcoma in the proximal tibia, the effect of pre-operative intra-arterial combination chemotherapy could not be increased, so amputation was required. He was changed to a post-operative intra-venous combination chemotherapy regimen selected by chemosensitivity test of the surgical material. All patients have been continuously disease-free at five to twelve months after surgery.

Fluorescence in situ hybridization analysis of chromosomal localization of three human cytochrome P450 2C genes (CYP2C8, 2C9, and 2C10) at 10q24.1

Chromosomal localization of three human cytochrome P450 genes belonging to the CYP2C subfamily (CYP2C8, 2C9, and 2C10) was identified by fluorescence in situ hybridization (FISH). An original MP-8 clone was used as a DNA probe for the assignment of the CYP2C10 gene, while two cDNA probes, a 1.37 kb fragment of CYP2C8 and a 1.19 kb fragment of CYP2C9, were obtained after amplifying the predicted fragments (MP-20 and MP-4 clones, respectively) by polymerase chain reaction using a single human liver cDNA library. The results showed that three human CYP2C8, 2C9, and 2C10 cDNAs were located at the same subchromosomal region, 10q24.1.

Monoclonal antibody to phosphatidylserine inhibits Na+/K(+)-ATPase activity

A monoclonal IgG, directed to phosphatidylserine (PS1G3), partially (40-50%) inhibited Na+/K(+)-ATPase activity (forward running reaction cycle) without affecting the K0.5 values for Na+,K+ and MgATP. The Hill or interaction coefficients (nH) for Na+ and K+ for this reaction were reduced from 3.0 to 1.6 and from 1.6 to 0.8, respectively. The K(+)-stimulated p-nitrophenylphosphatase activity (p-NPPase), which is a partial reaction sequence of the Na+/K(+)-ATPase system (but in the backward running mode), was inhibited more strongly (about 70%) due to an increase in K+/substrate antagonism. In this system K0.5 and nH values for both p-nitrophenyl phosphate (p-NPP) and K+ were increased by the mAb. At the maximally inhibitory concentration of PS1G3 the Vmax of the p-NPPase was also reduced. Partial reactions, which were inhibited by PS1G3, are: (1) the Na(+)-activated phosphorylation (non-competitive vs. Na+), (2) the Rb+ occlusion (competitive vs. Rb+). Partial reactions not harmed by PS1G3 are: (3) the K(+)-dependent dephosphorylation, (4) the K(+)-dependent E1 + K+<-->E2K transition. We conclude that PtdSer is involved in cation occlusion, possibly by forming part of the access gate.

Ultrasonically guided percutaneous microwave coagulation therapy for small hepatocellular carcinoma

BACKGROUND

The authors have used percutaneous microwave coagulation therapy (PMCT) as a new percutaneous local treatment for single unresectable hepatocellular carcinoma (HCC) measuring 2 cm or less in greatest dimension (small HCC). PMCT was used to attempt a cure of the disease. In this study, the efficacy of this treatment was assessed.

METHODS

PMCT was performed on 18 patients with single small HCC. A microwave electrode (custom-made, 30-cm long by 1.6-mm thick) was inserted percutaneously into the tumor area under ultrasonic guidance. Microwaves at 60 W for 120 seconds were used to irradiate the tumor and surrounding area.

RESULTS

After PMCT was administered, various image findings were correlated with tissue necrosis. At the tumor and surrounding area, ultrasonography showed echogenic change, contrast enhancement disappeared on contrast enhanced computed tomography, and magnetic resonance imaging (T2-weighted image) showed decreased intensity in all cases after treatment. Complete necrosis of the tumor area in a specimen obtained from one patient who underwent hepatectomy after PMCT also was confirmed. The treatment reduced levels of the tumor marker, alpha-fetoprotein, which had been high in some patients. Although the follow-up period was short (11-33 months), 17 patients remain alive. Local recurrence in the treated area has not been detected, and no serious side effects or complications have been encountered.

CONCLUSIONS

PMCT may be an effective and safe treatment for small HCCs.

Ultrasonically guided percutaneous microwave coagulation therapy for small hepatocellular carcinoma

BACKGROUND

The authors have used percutaneous microwave coagulation therapy (PMCT) as a new percutaneous local treatment for single unresectable hepatocellular carcinoma (HCC) measuring 2 cm or less in greatest dimension (small HCC). PMCT was used to attempt a cure of the disease. In this study, the efficacy of this treatment was assessed.

METHODS

PMCT was performed on 18 patients with single small HCC. A microwave electrode (custom-made, 30-cm long by 1.6-mm thick) was inserted percutaneously into the tumor area under ultrasonic guidance. Microwaves at 60 W for 120 seconds were used to irradiate the tumor and surrounding area.

RESULTS

After PMCT was administered, various image findings were correlated with tissue necrosis. At the tumor and surrounding area, ultrasonography showed echogenic change, contrast enhancement disappeared on contrast enhanced computed tomography, and magnetic resonance imaging (T2-weighted image) showed decreased intensity in all cases after treatment. Complete necrosis of the tumor area in a specimen obtained from one patient who underwent hepatectomy after PMCT also was confirmed. The treatment reduced levels of the tumor marker, alpha-fetoprotein, which had been high in some patients. Although the follow-up period was short (11-33 months), 17 patients remain alive. Local recurrence in the treated area has not been detected, and no serious side effects or complications have been encountered.

CONCLUSIONS

PMCT may be an effective and safe treatment for small HCCs.

Arrangement of fiber pieces for a wide wavelength conversion range by fiber four-wave mixing

A new technique is reported for obtaining a wide wavelength conversion range in fiber four-wave mixing. One fiber is cut into short fiber pieces and rearranged, considering the zero-dispersion wavelength of each fiber piece. With this rearrangement, the wavelength conversion range is expanded, compared with that in the original fiber. An experiment using a 6-km fiber confirms the technique.

Ultrasonically guided percutaneous microwave coagulation therapy for small hepatocellular carcinoma

BACKGROUND

The authors have used percutaneous microwave coagulation therapy (PMCT) as a new percutaneous local treatment for single unresectable hepatocellular carcinoma (HCC) measuring 2 cm or less in greatest dimension (small HCC). PMCT was used to attempt a cure of the disease. In this study, the efficacy of this treatment was assessed.

METHODS

PMCT was performed on 18 patients with single small HCC. A microwave electrode (custom-made, 30-cm long by 1.6-mm thick) was inserted percutaneously into the tumor area under ultrasonic guidance. Microwaves at 60 W for 120 seconds were used to irradiate the tumor and surrounding area.

RESULTS

After PMCT was administered, various image findings were correlated with tissue necrosis. At the tumor and surrounding area, ultrasonography showed echogenic change, contrast enhancement disappeared on contrast enhanced computed tomography, and magnetic resonance imaging (T2-weighted image) showed decreased intensity in all cases after treatment. Complete necrosis of the tumor area in a specimen obtained from one patient who underwent hepatectomy after PMCT also was confirmed. The treatment reduced levels of the tumor marker, alpha-fetoprotein, which had been high in some patients. Although the follow-up period was short (11-33 months), 17 patients remain alive. Local recurrence in the treated area has not been detected, and no serious side effects or complications have been encountered.

CONCLUSIONS

PMCT may be an effective and safe treatment for small HCCs.

Cloning of cDNAs for cecropins A and B, and expression of the genes in the silkworm, Bombyx mori

cDNA clones coding cecropins A and B were isolated from a cDNA library constructed from the fat body of immunized Bombyx mori larvae. The cloned cDNAs had an open reading frame of 63 amino acids, indicating the primary translated peptides were processed to form mature cecropins of 35 amino acid residues. The homology in the coding regions of cecropins A and B was 73%. In immunized fat body, the expression of both cecropin A and B genes reached the maximal level 5 h after the injection of soluble peptidoglycan, and the high level was maintained until 9 h after immunization. The cecropin A and B genes were expressed at high levels in fat body and hemocytes, at lower but significant levels in malpighian tube, slightly in midgut, and none in silk gland.

Induction of extrahepatic biliary carcinoma by N-nitrosobis(2-oxopropyl)amine in hamsters given cholecystoduodenostomy with dissection of the common duct

The methods we used to produce a carcinoma in the extrahepatic bile duct and gallbladder in hamsters are described along with the characteristics of the induced tumors. Female Syrian golden hamsters were first subjected to cholecystoduodenostomy with dissection of the extrahepatic bile duct on the distal end of the common duct (CDDB) and were, 4 weeks later, treated with weekly subcutaneous injections of N-nitrosobis(2-oxopropyl)amine (BOP) at a dose of 10 mg/kg body weight for 9 weeks. The animals were killed at the 12th, 16th and 20th week after the initiation of BOP treatment. Extrahepatic bile duct carcinoma developed in 16%, 24% and 41% and gallbladder carcinoma occurred in 58%, 81% and 82% of the hamsters, respectively, at the corresponding times of killing. The incidences were significantly higher than those in sham-operated controls (P < 0.01). The induced extrahepatic bile duct carcinomas were predominantly of the polypoid type and gallbladder carcinomas were of the papillary type in growth form, being morphologically similar to early stage biliary carcinoma in humans. Immunohistochemical staining using bromodeoxyuridine and anti-bromodeoxyuridine monoclonal antibody demonstrated that the CDDB procedure greatly accelerated the cell kinetic activity of the biliary epithelium, and this was considered to be a major factor promoting the development of biliary carcinomas in this hamster model. In conclusion, this new model provides a high incidence of tumor development at the extrahepatic biliary tract and is expected to be useful for clarifying the characteristics of this highly malignant tumor.

[Clinical evaluation of changes in serum zinc and copper concentrations around pulmonary operation]

Serum zinc and copper were measured in 47 patients undergoing pulmonary operation. They were divided into two groups according to the extent of the operation. Group A consisted of 32 patients with lung cancer, in whom lobectomy with lymphadenectomy was performed through the postero-lateral thoracotomy. Group B consisted of 15 patients with benign pulmonary lesion or metastatic pulmonary tumor, in whom wedge resection was performed through the axillary thoracotomy. In Group A, the serum zinc concentration most decreased 6 hours after surgery. It returned to normal level in 5-7 days and to the preoperative level within 14 days. In Group B, the maximal fall in serum zinc was at 3 hours after operation. Restoration to normal level was at 2nd postoperative day and to the preoperative level was at 5th postoperative day. The differences in serum zinc between two groups were significant (p < 0.05) from just after operation to 4th postoperative day. The degree of maximal decrease in serum zinc in Group A was more than that in Group B. Blood loss, operation time and pulmonary function did not influenced the change of serum zinc concentration in our series. These results show that degree and duration of reduction in serum zinc depends on the surgical trauma. On the other hand, no significant difference in serum copper levels was observed between two groups. The influence of pre- and post-operative pneumonia on serum zinc concentrations were followed in 3 patients. Fall and rise in serum zinc levels coincided with manifestation of and recovery from pneumonia.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of an established transplantable adenocarcinoma of the gallbladder in Syrian golden hamster

A carcinoma of the gallbladder was transplantable in Syrian golden hamsters. The tumor was induced by subcutaneous injection of N-nitrosobis (2-oxopropyl) amine (BOP) following dissection of the common duct and preparation of a cholecysto-duodenostomy. The histology revealed a poorly differentiated adenocarcinoma. The tumor was inoculated into the cavity of the gallbladder and subcutaneous tissue of the hamster and was transplantable (uptake rate was 100%). This tumor expressed blood group-related antigens, including A, H, and P-glycoproteins. To our knowledge, this is the first report of carcinoma of the gallbladder transplantable in a laboratory animal.

Suppressive effects of the anti-allergic drugs, tranilast and azelastine, on the lysophosphatidylserine-dependent activation of rat mast cells

Anti-allergic drugs, tranilast and azelastine, were examined for their effects on lysophosphatidylserine (lysoPS)-dependent histamine release from rat mast cells. Although both compounds suppressed the histamine release in a dose-dependent manner, the inhibition was affected by lysoPS concentration differently. In the presence of an increasing concentration of lysoPS, the suppressive effect of tranilast decreased. The inhibition by azelastine, however, was independent of the concentration of lysoPS. The findings suggest that these two drugs inhibit lysoPS-depedent histamine release through essentially different routes.

A novel peptide probe for studying the transbilayer movement of phosphatidylethanolamine

Ro09-0198 is a cyclic peptide isolated from Streptoverticillium griseoverticillatum which recognizes strictly the structure of phosphatidylethanolamine (PE) and forms an equimolar complex with the phospholipid on biological membranes. To use the peptide as a probe for analyzing the transbilayer movement of PE, we labeled the amino-terminal amino acid of the peptide with biotin without changing either the reactivity or specificity of the peptide. The amount of the peptide bound to the membrane was measured by enzyme linked immunosorbent assay (ELISA) after extraction of the peptide from the membrane. The peptide showed a strict temperature-dependent binding to human erythrocytes and the binding increased with increasing temperature. Since the peptide bound to PE in a temperature-independent manner and the binding to membrane PE is not affected by membrane proteins, the present temperature-dependent binding of the peptide to the cell membranes was likely to reflect temperature-dependent translocation of PE. The binding of the peptide to erythrocytes differed greatly among animal species. The peptide also showed temperature-dependent binding to a human histocytic lymphoma cell line, U937, suggesting that the peptide will provide a novel and convenient probe for analyzing the transbilayer movement of PE in eukaryotic cells.

Miller-Dieker lissencephaly gene encodes a subunit of brain platelet-activating factor acetylhydrolase [corrected]

Platelet-activating factor (PAF) is involved in a variety of biological and pathological processes and PAF acetylhydrolase, which inactivates PAF by removing the acetyl group at the sn-2 position, is widely distributed in plasma and tissue cytosols. One isoform of PAF acetylhydrolase present in bovine brain cortex is a heterotrimer comprising subunits with relative molecular masses of 45K, 30K and 29K (ref. 4). We have now isolated the complementary DNA for the 45K subunit. Sequence analysis revealed a striking identity (99%) of the subunit with a protein encoded by the causative gene (LIS-1) for Miller-Dieker lissencephaly, a human brain malformation manifested by a smooth cerebral surface and abnormal neuronal migration. This indicates that the LIS-1 gene product is a human homologue of the 45K subunit of intracellular PAF acetylhydrolase. Our results raise the possibility that PAF and PAF acetylhydrolase are important in the formation of the brain cortex during differentiation and development.

Dual regulation of cytosolic phospholipase A2 in mast cells after cross-linking of FC epsilon-receptor

We have reported previously that cultured mast cells (MC) express three discrete phospholipases A2 (PLA2s), one of which corresponds to arachidonoyl-preferential cytosolic PLA2 (cPLA2). In the present study, we investigated the possible role of cPLA2 in eicosanoid synthesis by activating mouse bone marrow-derived mast cells (BMMC) through cross-linking of the high affinity IgE receptor (Fc epsilon RI) with a specific Ag. BMMC released arachidonic acid within 2 min after Fc epsilon RI cross-linking. A rapid, transient phosphorylation of cPLA2 was observed after Fc epsilon RI cross-linking, reaching the maximum within 2 min, and accompanied by an increase of cPLA2 activity in the cell lysate. Exposure of BMMC to the IgE-Ag for longer periods resulted in a time-dependent increase of the cPLA2 protein. The increase was detected within 10 h after stimulation and reached the maximum within 30 h. Dexamethasone inhibited the Ag-stimulated cPLA2 induction significantly. cPLA2 activity in cells stimulated for 24 h was increased significantly, and suppressed in cells treated with dexamethasone. When the cells were exposed to IgE-Ag for 36 h and then challenged with a secondary agonist, thrombin, arachidonate release was augmented significantly in comparison with cells without the Ag pretreatment. Thus, cPLA2 activation in BMMC by short term exposure to the Ag might be regulated by post-Fc epsilon RI modification (phosphorylation) of pre-existing enzyme, whereas that observed after long term exposure might be explained by the increase in cPLA2 protein.

Dual regulation of cytosolic phospholipase A2 in mast cells after cross-linking of FC epsilon-receptor

We have reported previously that cultured mast cells (MC) express three discrete phospholipases A2 (PLA2s), one of which corresponds to arachidonoyl-preferential cytosolic PLA2 (cPLA2). In the present study, we investigated the possible role of cPLA2 in eicosanoid synthesis by activating mouse bone marrow-derived mast cells (BMMC) through cross-linking of the high affinity IgE receptor (Fc epsilon RI) with a specific Ag. BMMC released arachidonic acid within 2 min after Fc epsilon RI cross-linking. A rapid, transient phosphorylation of cPLA2 was observed after Fc epsilon RI cross-linking, reaching the maximum within 2 min, and accompanied by an increase of cPLA2 activity in the cell lysate. Exposure of BMMC to the IgE-Ag for longer periods resulted in a time-dependent increase of the cPLA2 protein. The increase was detected within 10 h after stimulation and reached the maximum within 30 h. Dexamethasone inhibited the Ag-stimulated cPLA2 induction significantly. cPLA2 activity in cells stimulated for 24 h was increased significantly, and suppressed in cells treated with dexamethasone. When the cells were exposed to IgE-Ag for 36 h and then challenged with a secondary agonist, thrombin, arachidonate release was augmented significantly in comparison with cells without the Ag pretreatment. Thus, cPLA2 activation in BMMC by short term exposure to the Ag might be regulated by post-Fc epsilon RI modification (phosphorylation) of pre-existing enzyme, whereas that observed after long term exposure might be explained by the increase in cPLA2 protein.

Dual modulation by adenosine of ATP-activated channels through GTP-binding proteins in rat pheochromocytoma PC12 cells

Effects of adenosine on inward current activated by extracellular ATP were examined in rat pheochromocytoma PC12 cells. Adenosine induced two types of modulation on the current activated by 30 microM ATP; a low concentration of adenosine (1 microM) inhibited the current whereas a high concentration (> 10 microM) enhanced the current. Neither the inhibition nor the enhancement was observed in cells pretreated with pertussis toxin (PTX), or in cells dialyzed with guanosine 5'-O-(2-thiotriphosphate) trilithium salt (GDP beta S). In contrast, dialysis with K-252a, a protein kinase inhibitor, abolished the inhibition, but not the enhancement. Adenosine induced similar inhibition and enhancement on ATP-evoked increase in intracellular free Ca2+ concentration. The results suggest that adenosine produces dual modulation on the ATP-activated channels through different mechanisms involving PTX-sensitive GTP-binding proteins.

Structure-specific inhibition of lysosomal cholesterol transport in macrophages by various steroids

Cultured mouse peritoneal macrophages effectively take up and metabolize liposomes containing phosphatidylserine and cholesterol, resulting in massive accumulation of cholesteryl esters and triacylglycerols in their cytoplasm (Nishikawa, K., Arai, H. and Inoue, K. (1990) J. Biol. Chem. 265, 5226-5231). With this system, various steroid derivatives were assessed as to their ability to inhibit the cholesteryl ester formation from endocytosed cholesterol in macrophages. Among the steroids tested, one group of steroids having an oxo group at the C17 or C20 position, such as androstenedione, dehydroisoandrosterone, progesterone and pregnenolone, completely inhibited cholesteryl ester formation at 10 microM. Another group of steroids having a hydroxy group at the C17 position, such as testosterone and androstenediol, had a lesser effect; complete inhibition of cholesteryl ester formation was achieved with 100 microM or more. The mechanism underlying the inhibition by the former class of steroids was further studied. These steroids did not block the uptake or lysosomal hydrolysis of liposomes, nor esterification of fatty acyl chains into triacylglycerols. Moreover, dehydroisoandrosterone and pregnenolone, both of which possess a hydroxy group at the C3 position, had essentially no effect on 25-hydroxycholesterol-stimulated esterification of endogenous cellular cholesterol. On the other hand, androstenedione and progesterone, which possess an oxo group at the C3 position, had a mild inhibitory effect on the esterification of endogenous cholesterol. Upon incubation with a steroid having an oxo group at the C17 or C20 position, free cholesterol taken up by macrophages was accumulated in phagolysosomes, as judged from cytochemical study with filipin-cholesterol staining. These results indicate that a series of structurally-related steroids characterized by the presence of an oxo group at the C17 or C20 position inhibit cholesteryl ester formation in macrophages through blocking the intracellular transport of endocytosed cholesterol from lysosomes to endoplasmic reticulum.

[Interferon treatment of type C fulminant hepatitis]

On the contrary to Western countries, there are a substantial number of patients with type C fulminant hepatitis (FH) including coinfection on type A and type B hepatitis in Asian countries. The pathogenesis of FH is not fully understood, however, recent clinical observations suggest that enhanced host immune responses contribute to hepatocyte destruction in type C FH. In contrast to type B FH, type C FH is characterized by gradual and continuous liver necrosis probably duo to persistent infection of hepatitis C virus. Administration of interferon with immunosuppressive agents is the treatment of choice. Prognosis may be improved if the treatment is started in the early stage of the disease.

GABA-ergic and substance P-ergic double-innervation to noradrenergic neurons in the rat locus coeruleus

Synaptic contacts between noradrenaline (NA) neurons and GABA (gamma-aminobutyric acid) afferents and/or substance P (SP) afferents in the locus coeruleus (LC) were examined by a combination of immunoelectron microscopic mirror method and double-immunostaining method. For visualization of NA and GABA, we used antibodies against NA and GABA synthesizing enzymes, i.e., tyrosine hydroxylase (TH) and glutamic acid decarboxylase (GAD). GAD-immunoreactive (IR) and SP-IR axon terminals often made synaptic contacts with NA neurons, respectively. Furthermore, we identified that a single NA neuron simultaneously receives synaptic inputs from GAD-IR and SP-IR afferents. These NA neurons made symmetrical synaptic contacts with GAD-IR axon terminals and asymmetrical contacts with SP-IR axon terminals. This suggests that central NA neuronal mechanisms are affected by GABA and SP neurons in a different manner.

Immunohistochemical study of cathepsin B. Prognostic significance in human lung cancer

BACKGROUND

The concentration of cysteine proteinase cathepsin B has been shown to be elevated in association with malignancy or metastatic potential of human and rodent tumors, but its prognostic value for human lung cancer remains undetermined.

METHODS

Using a polyclonal antibody, immunohistochemical analyses of cathepsin B were performed on paraffin embedded sections of tumors obtained surgically from 108 patients with non-small cell lung cancer (49 squamous cell carcinomas, 59 adenocarcinomas). The immunohistochemical expressions of cathepsin B in the tumors were compared with patient survival.

RESULTS

Higher grade expression of cathepsin B was associated significantly with shorter survival in non-small cell lung cancer (P < 0.01), in squamous cell carcinoma (P < 0.05), and in adenocarcinoma (P < 0.01). A similar result also was seen in Stage I non-small cell lung cancer (P < 0.05).

CONCLUSIONS

The authors concluded that the immunohistochemical staining pattern of cathepsin B may be a useful predictor of survival for human lung cancer.

Potentiation by adenosine of ATP-evoked dopamine release via a pertussis toxin-sensitive mechanism in rat phaeochromocytoma PC12 cells

1. The effects of adenosine on adenosine 5'-triphosphate (ATP)-evoked dopamine release from rat phaeochromocytoma PC12 cells was investigated to determine whether adenosine exerts a regulatory effect on the ATP-evoked response. Adenosine potentiated ATP (30 microM)-evoked dopamine release in a concentration-dependent manner over a concentration-range of 1 to 100 microM. Adenosine (100 microM) shifted the concentration-dependence of the ATP-evoked response to the left without affecting the maximal response. 2. Aminophylline, a non-selective adenosine receptor antagonist, and CP66713, a selective antagonist at the A2 subclass of adenosine receptors, abolished the adenosine-induced potentiation. Furthermore, 8-cyclopentyltheophylline, a selective antagonist at the adenosine A1 receptor partially inhibited the adenosine-evoked potentiation. CGS22492, a selective A2 receptor agonist, potentiated ATP-evoked dopamine release whereas N6-cyclohexyladenosine (CHA), a selective A1 receptor agonist, had no effect. 3. Pertussis toxin (PTX), a bacterial exotoxin which catalyzes the ADP-ribosylation of guanosine 5'-triphosphate (GTP)-binding proteins (G-proteins), inhibited the adenosine-induced potentiation of dopamine release. Dibutyryl cyclic AMP (db cyclic AMP), an analogue of cyclic AMP, had no effect on the release on the ATP-evoked response. 4. Adenosine potentiated the ATP-evoked rise in intracellular Ca2+ concentration ([Ca]i) in PC12 cells. This potentiation was also observed with CGS 22492 but not with CHA. PTX completely inhibited the adenosine-induced potentiation of the rise in [Ca]i. 5. On the basis of these findings, we suggest that the adenosine-induced potentiation of ATP-evoked dopamine release was due to an increase in [Ca]i in the cells. Although the potentiation is most likely mediated by a subclass of A2 receptors, the subclass may be different from those previously reported since the potentiation was sensitive to PTX and was not reproduced by db cyclic AMP.

Facilitation by 5-hydroxytryptamine of ATP-activated current in rat pheochromocytoma cells

The effects of 5-hydroxytryptamine (5-HT) on an inward current activated by extracellular ATP were investigated in rat pheochromocytoma PC12 cells. Under whole-cell voltage-clamp conditions 5-HT (10 microM) reversibly enhanced the amplitude of the current activated by 30 microM ATP. The enhancement may not be due to an increase in the number of functional channels because the current activated by 300 microM ATP was not remarkably augmented compared with the current activated by 30 microM ATP. The current enhancement by 100 microM 5-HT was less obvious than that by 10 microM 5-HT. When the current kinetics were compared, activation of the ATP-evoked current was accelerated to the same extent by either 10 or 100 microM 5-HT, whereas deactivation was largely more accelerated by 100 microM 5-HT. Propranolol (10 microM), a 5-HT1 receptor antagonist, or LY53857 (10 microM), a 5-HT2 receptor antagonist, exerted an agonistic effect: the ATP-activated current was facilitated by these compounds. Metoclopramide (10 microM), a 5-HT3 receptor antagonist, neither facilitated the ATP-activated current, nor blocked the current facilitation by 5-HT. Guanosine 5'-O-(2-thiodiphosphate) (GDP[beta S]) (2 mM), the non-hydrolysable analog of guanosine 5'-triphosphate (GTP), or K-252a (2 microM), a protein kinase inhibitor, did not affect the facilitation by 5-HT of the ATP-activated current when they were included in the intracellular solution. The ATP-activated current pre-facilitated by 10 microM dopamine was not enhanced by 10 microM 5-HT. Similarly, the pre-facilitation by 5-HT attenuated the current enhancement by dopamine.(ABSTRACT TRUNCATED AT 250 WORDS)