ATP is released from rabbit urinary bladder epithelial cells by hydrostatic pressure changes--a possible sensory mechanism?

1. The responses of rabbit urinary bladder to hydrostatic pressure changes and to electrical stimulation have been investigated using both the Ussing chamber and a superfusion apparatus. These experiments enabled us to monitor changes in both ionic transport across the tissue and cellular ATP release from it. 2. The urinary bladder of the rabbit maintains an electrical potential difference across its wall as a result largely of active sodium transport from the urinary (mucosal) to the serosal surface. 3. Small hydrostatic pressure differences produced by removal of bathing fluid from one side of the tissue caused reproducible changes in both potential difference and short-circuit current. The magnitude of these changes increases as the volume of fluid removed increases. 3. Amiloride on the mucosal (urinary), but not the serosal, surface of the membrane reduces the transepithelial potential difference and short-circuit current with an IC50 of 300 nM. Amiloride reduces the size of, but does not abolish, transepithelial potential changes caused by alterations in hydrostatic pressure. 4. Field electrical stimulation of strips of bladder tissue produces a reproducible release of ATP. Such release was demonstrated to occur largely from urothelial cells and is apparently non-vesicular as it increases in the absence of calcium and is not abolished by tetrodotoxin. 5. It is proposed that ATP is released from the urothelium as a sensory mediator for the degree of distension of the rabbit urinary bladder and other sensory modalities.

A randomized study of paclitaxel versus cyclophosphamide/methotrexate/5-fluorouracil/prednisone in previously untreated patients with advanced breast cancer: preliminary results. Taxol Investigational Trials Group, Australia/New Zealand

When administered as a single agent to previously treated patients with advanced breast cancer, paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) has good activity. This trial was undertaken to compare paclitaxel with standard chemotherapy as front-line treatment for this disease. Patients with measurable or evaluable metastatic breast cancer, no prior chemotherapy for metastatic disease, and Eastern Cooperative Oncology Group performance status of 0 to 2 were randomized to receive either paclitaxel 200 mg/m2 intravenously over 3 hours for eight cycles over 24 weeks or standard treatment with oral cyclophosphamide 100 mg/m2/d days 1 to 14, intravenous methotrexate 40 mg/m2 days 1 and 8, intravenous 5-fluorouracil 600 mg/m2 days 1 and 8, and oral prednisone 40 mg/m2 daily days 1 to 14 (CMFP) for six cycles over 24 weeks. Patients whose disease progressed or relapsed were recommended for second-line therapy with epirubicin. Accrual has been completed with 209 patients randomized, and an interim analysis of the first 100 patients is reported here. Analysis of quality of life, assessed by the linear analogue scale and overall quality of life indices, is ongoing. Objective response occurred in 31% (confidence interval, 19% to 45%) with paclitaxel and 35% (confidence interval, 22% to 51%) with CMFP, with stable disease in an additional 33% and 29%, respectively. Median time to progression was 5.5 months with paclitaxel and 6.4 months with CMFP, with a median survival of 17.3 months for patients treated with paclitaxel and 11.3 months for those given CMFP. Grades 3 and 4 neutropenia occurred in 64% of patients with paclitaxel and 63% with CMFP. However, febrile neutropenia was the primary reason for hospitalization in 1% of paclitaxel courses, compared with 8% with CMFP. Major infections (World Health Organization grade 4) were seen in 7% of patients treated with CMFP, but in none of those given paclitaxel. Moderate or severe mucositis occurred in 13% of paclitaxel and 27% of CMFP patients. Alopecia and peripheral neuropathy were more common with paclitaxel. Quality of life assessments in the first 100 patients suggest better overall results for those treated with paclitaxel compared with CMFP. Preliminary analyses suggest that single-agent paclitaxel is well tolerated and provides control of metastatic cancer comparable to that of CMFP combination therapy when used as front-line therapy in an outpatient setting.

Paclitaxel as first-line treatment for metastatic breast cancer. The Taxol Investigational Trials Group, Australia and New Zealand

When administered as a single agent in pretreated patients with advanced breast cancer, paclitaxel (Taxol) exhibits remarkable antitumor activity. This trial was undertaken to compare paclitaxel with standard chemotherapy as front-line therapy for this disease. Patients with measurable or evaluable metastatic breast cancer, no prior chemotherapy for metastatic disease, and an Eastern Cooperative Oncology Group performance status of 0 to 2 were randomized to receive paclitaxel 200 mg/m2 intravenously over 3 hours for eight cycles (6 months) or standard treatment with oral cyclophosphamide (Cytoxan) 100 mg/m2/d days 1 through 14, intravenous methotrexate 40 mg/ m2 days 1 and 8, intravenous 5-fluorouracil 600 mg/m2 days 1 and 8, and oral prednisolone 40 mg/m2/d (CMFP) days 1 through 14 for six cycles (6 months). Patients whose disease progressed or relapsed were recommended to receive second-line epirubicin. Accrual has been completed with 208 patients randomized, but a preplanned interim analysis of the first 100 patients is reported here. Analysis of quality of life, assessed by a linear analogue scale and overall quality of life indices, is ongoing. Objective response occurred in 31% (confidence interval, 19% to 45%) with paclitaxel and 35% (confidence interval, 22% to 51%) with CMFP with stable disease in an additional 33% and 29%, respectively. Median time to progression was 5.5 months for paclitaxel-treated patients and 6.4 months for those given CMFP, with median survival durations of 17.3 and 11.3 months, respectively. Grades 3 and 4 neutropenia occurred in 64% of patients treated with paclitaxel and in 63% treated with CMFP. However, febrile neutropenia was the primary reason for hospitalization in 1% of paclitaxel courses, compared with 8% of CMFP courses. Nine percent of the patients had major infections with CMFP, but none were seen with paclitaxel. Moderate or severe mucositis occurred in 13% of paclitaxel-treated and 27% of CMFP-treated patients. Alopecia and peripheral neuropathy were more common with paclitaxel. Quality of life assessments in the first 100 patients suggest better overall results on paclitaxel treatment as compared with CMFP. Preliminary analyses suggest that single-agent paclitaxel is well tolerated and provides comparable control of metastatic cancer to CMFP combination therapy when used as front-line treatment.

New insights on P2X purinoceptors

Significant advances in understanding of P2X purinoceptor pharmacology have been made in the last few years. The limitations of nucleotide agonists as drug tools have now been amply demonstrated. Fortunately, inhibitors of the degrading ecto-ATPase enzymes are becoming available and it has become apparent that the complete removal of all divalent cations can be used experimentally in some systems to prevent nucleotide breakdown. Despite these issues, convincing evidence for P2X receptor heterogeneity, from data with agonists, has recently been reported. A number of new antagonists at P2X purinoceptors have also recently been described which to some degree appear to be more specific and useful than earlier antagonists like suramin. It is now apparent that suramin is a poor antagonist of ATP in many tissues because it potently inhibits ATPase activity at similar concentrations to those at which it blocks the P2X purinoceptor. Advances in the use of radiolabelled nucleotides as radioligands for binding studies has allowed the demonstration of P2X purinoceptors in a variety of tissues throughout the body including the brain. These studies have also provided evidence for receptor heterogeneity. Excitingly, two P2X purinoceptor genes have been cloned but operational studies suggest that more than two types exist. The cloning studies have also demonstrated a unique structure for the P2X purinoceptor which differentiates it from all other ligand-gated ion channel receptors. Further studies on P2X purinoceptor operation and structure are needed to help resolve controversies alluded to regarding the characterization and classification of nucleotide receptors. Hopefully such studies will also lead to a better understanding of the physiological and pathological importance of ATP and its activation of P2X purinoceptors. This will require the identification of better drug tools, in particular antagonists which may also provide the basis for novel therapeutic agents.

Implantation of sutured posterior chamber intraocular lenses

We describe a technique for implanting sutured posterior chamber intraocular lenses. Results of a small series using this technique in different clinical situations with at least 12 months follow-up are presented.

Effects of divalent cations on the potency of ATP and related agonists in the rat isolated vagus nerve: implications for P2 purinoceptor classification

1. By use of a 'grease-gap' technique, the depolarizing effects of adenosine 5'-triphosphate (ATP) and ATP analogues on the rat isolated vagus nerve were determined in normal and in Ca2+/Mg(2+)-free (+ 1 x 10(-3) M ethylenediamine tetraacetic acid) physiological salt solution (PSS). 2. In normal PSS, ATP produced concentration-dependent depolarization responses but the concentration-effect curve to ATP was incomplete and a maximum effect was not achieved. The threshold concentration for depolarization was 1 x 10(-5) M and at the highest concentration tested (1 x 10(-3) M) the peak amplitude of the response to ATP only amounted to 71% of the depolarization produced by a near maximal response to 5-hydroxytryptamine (5-HT, 1 x 10(-5) M). 3. In Ca2+/Mg(2+)-free PSS, ATP produced depolarization responses at much lower concentrations and of markedly larger amplitude. Under these conditions, the threshold concentration for depolarization was 1-3 x 10(-7) M and the maximal response to ATP amounted to 526% of the response to 5-HT (1 x 10(-5) M) in normal PSS. The concentration-effect curve to ATP was sigmoid, with a defined maximum effect and a mean EC50 value of 1.2 x 10(-6) M. 4. In contrast to the effects on responses to ATP, the absence of divalent cations in the PSS did not modify the effective concentrations of either alpha, beta-methylene ATP or 5-HT. However, the maximum responses to both alpha, beta-methylene ATP and 5-HT were significantly increased in Ca2+/Mg(2+)-free PSS. 5. The depolarizing effects of several analogues of ATP were determined in Ca2+/Mg2+-free PSS.ATP-gamma-S and 2-methylthioATP were of similar potency to ATP (respective equi-effective molar ratios(EMRs) of 1.9 and 1.3, where ATP = 1) and similar maximum responses were obtained. Alpha, beta-MethyleneATP, beta, gamma-methylene ATP and ,beta, gamma-imido ATP were considerably less potent than ATP, analysis yielding mean EMRs of 48.9, 85.0 and 60.0, respectively. Maximum responses to these latter three agonists were not obtained at the highest concentrations tested (1 x 10-4-3 X 10- M). Benzoyl ATP, adenosine 5'-0-(2-thiodiphosphate) and adenosine diphosphate produced only small depolarizing responses at high concentrations (>1 x 10-4 M). Adenosine monophosphate, adenosine and uridine S'-triphosphate each had little or no depolarizing effect in Ca2+/Mg2+-free PSS.6. These data demonstrate that in the absence of divalent cations the excitatory actions of some, but not all, purine nucleotides in the rat vagus nerve are markedly potentiated. In Ca2+/Mg2+-free PSS, the rank order of agonist potencies was ATP = 2-methylthioATP = ATP-gamma-S>> alpha,beta-methylene ATP = beta, gamma imido ATP = P,y-methylene ATP. These findings are in stark contrast to our previous observations in normal PSS where the rank order of agonist potencies for these nucleotides was alpha,beta-methyleneATP> ATP-gamma-S > beta,gamma-imido ATP = beta,gamma-methylene ATP> 2-methylthioATP> ATP.7. We suggest that the two different rank orders of potency can be explained by differential metabolism involving Ca2+/Mg2+-dependent ectonucleotidases. If so, these data indicate that ATP and 2-methylthioATP are inherently more potent than alpha,beta-methylene ATP as agonists at neuronal P2X purinoceptors in the rat vagus nerve. The possible implications of these findings to the present system for subclassifying P2 purinoceptors are profound.

Evidence for the presence of two types of P2 purinoceptor in the guinea-pig ileal longitudinal smooth muscle preparation

The effects of some agonists acting at P2 purinoceptors on guinea-pig isolated ileum longitudinal smooth muscle have been examined. The preparation contracted in response to ATP, alpha,beta-methylene ATP and 2-methylthio ATP, but not UTP. In this respect, alpha,beta-methylene ATP and 2-methylthio ATP were approximately equipotent and both were 10-50 times more active than ATP. Responses to alpha,beta-methylene ATP, but not 2-methylthio ATP or ATP, were antagonised by atropine and tetrodotoxin, suggesting that alpha,beta-methylene ATP activates cholinergic nerves in the ileum, whilst the other two compounds act on the smooth muscle. Two other purine nucleotide analogues, beta,gamma-methylene ATP and beta,gamma-imido ATP, did not cause contraction. However, both compounds antagonised responses to alpha,beta-methylene ATP, but not those to 2-methylthio ATP. Suramin antagonised responses to both alpha,beta-methylene ATP and 2-methylthio ATP, whilst Cibacron blue was without effect on responses to either agonist. We conclude that the purinoceptor on cholinergic nerves has some of the characteristics of the P2x purinoceptor, whilst the purinoceptor on ileal smooth muscle has some of the characteristics of the P2Y purinoceptor. However, further work will be necessary before definitive classification is possible.

The use of antagonists to characterize the receptors mediating depolarization of the rat isolated vagus nerve by alpha, beta-methylene adenosine 5'-triphosphate

1. We have previously found that the P2x-purinoceptor agonist, alpha, beta-methylene adenosine 5'-triphosphate (alpha, beta-methylene ATP), depolarizes the rat cervical vagus nerve, measured with a 'grease-gap' extracellular recording technique. This effect was attenuated by the P2 purinoceptor antagonist, suramin. In the present study we have investigated in more detail the antagonism produced by suramin and have also investigated the actions of two other putative P2 purinoceptor antagonists, cibacron blue and pyridoxal-phosphate-6-azophenyl-2', 5'-disulphonic acid (iso-PPADS). Furthermore, we have studied the interactions between suramin and cibacron blue or iso-PPADS in an attempt to determine whether these antagonists act at a common receptor site. 2. Suramin (1 x 10(-5)-1 x 10(-4) M) produced reversible, concentration-related rightward displacements of the concentration-effect curve to alpha, beta-methylene ATP. Schild analysis of this antagonism yielded a pA2 value of 5.90 with a slope value of 0.47. 3. Cibacron blue (3 x 10(-5)-1 x 10(-4) M) also antagonized depolarizations induced by alpha, beta-methylene ATP. The antagonistic effects of cibacron blue were slow to reach equilibrium but could be readily reversed on washout. At low concentrations for antagonism, cibacron blue (1 x 10(-5) M and 3 x 10(-5) M) produced enhancement of the maximal response to alpha, beta-methylene ATP. At the highest concentration tested (1 x 10(-4) M) the concentration-effect curve to alpha, beta-methylene ATP was shifted to the right in a parallel manner, yielding a pKB estimate of 4.96. 4. Iso-PPADS (1 X 10-6 1 X 10-5- M) produced a concentration-related depression in the maxima ofthe concentration-effect curves to alpha,beta-methylene ATP. Analysis of these data by a double reciprocal plot yielded a pKB estimate of 6.02. This profile of insurmountable antagonism could not be attributed to irreversible binding of iso-PPADS to the receptor since the effect of iso-PPADS could be reversed on washing, albeit slowly.5. In the presence of suramin (1 x 10-4 M), cibacron blue (1 x 10-4 M) produced no further rightward displacement of the alpha,beta-methylene ATP concentration-effect curve. The mean agonist concentration ratios in the presence of suramin or cibacron blue alone (11.7 and 10.3, respectively) were not significantly different from the mean concentration-ratio in the presence of both antagonists (11.8). This finding suggests that high concentrations of alpha,beta-methylene ATP activate a receptor population which is resistant to blockade by either antagonist.6. The antagonistic effect of iso-PPADS (1 x 10-5 M) was partially attenuated by suramin (1I x 10-4 M).It is possible that this interaction reflects a slow dissociation of iso-PPADS from the receptor with which suramin and alpha,beta-methylene ATP interact.7. Suramin, cibacron blue or iso-PPADS had no marked effect on depolarization produced by 5-hydroxytryptamine (5-HT, 1 x 10-7-3 x 10-5 M), indicating their specificity in antagonizing responses to alpha, beta-methylene ATP.8. Responses to alpha,beta-methylene ATP were not antagonized by 8-para-sulphophenyltheophylline (3 x 10-5M), ondansetron (1 x 10-7 M), bicuculline (1 x I0-5 M), phentolamine (1 X 10-6 M) or hexamethonium(1 X 10-4 M), which are antagonists at P1-purinoceptors, 5-HT3 receptors, GABAA receptors, a-adrenoceptors and nicotinic cholinoceptors, respectively, thereby excluding the involvement of these receptors.Indomethacin (3 X 10-6 M) had no effect on responses to alpha,beta-methylene ATP.9. The results obtained with three purinoceptor antagonists confirm and extend our original supposition that alpha,beta-methylene ATP-induced depolarization of the rat vagus nerve is mediated predominantly via P2 purinoceptors, thought to be of the P2,X subtype. The finding that responses induced by high concentrations of agonist were resistant to blockade by suramin and cibacron blue, but could be attenuated by iso-PPADS, adds further weight to our speculation that the purinoceptor population in the rat vagus nerve is heterogeneous.

Characterization of purinoceptors mediating depolarization of rat isolated vagus nerve

1. As part of a broader study to characterize neuronal purinoceptors, the effects of adenosine 5'-triphosphate (ATP) and a range of ATP analogues were investigated on the extracellularly recorded membrane potential of the rat isolated vagus nerve, using a 'grease-gap' technique. 2. ATP evoked depolarization of the rat vagus nerve. The concentration-effect curve to ATP was not monophasic: at the lower concentrations (1 x 10(-5)-1 x 10(-3) M) the curve was shallow (< 50% of the near maximal response to 5-hydroxytryptamine (5-HT)) whilst at higher concentrations the relationship between concentration and amplitude of depolarization was steeper (> 135% of the response to 5-HT at the highest concentration tested, 1 x 10(-2) M). On washout of the high drug concentrations large after-hyperpolarizations were often observed. 3. alpha,beta-methylene ATP (1 x 10(-6)-3 x 10(-4) M), beta,gamma-methylene ATP (1 x 10(-6)-1 x 10(-3) M), and 5'-adenylylimidodiphosphate (beta,gamma-imido ATP; 1 x 10(-6)-1 x 10(-3) M) were all more potent than ATP and produced large depolarizations of the rat vagus nerve at the highest concentrations tested (> 150% of the response to 5-HT). The overall rank order of potency was alpha,beta-methylene ATP > beta,gamma-methylene ATP = beta,gamma-imido ATP > ATP. 4. In contrast, 2-methylthio ATP (1 x 10(-6)-1 x 10(-3) M) produced relatively small depolarizations (< 100% of the response to 5-HT). As was the case with low concentrations of ATP, the concentration-effect curve to 2-methylthio ATP was very shallow. 5. Adenosine 5'-diphosphate (ADP), adenosine 5'-monophosphate (AMP), adenosine and adenosine 5'-O-(2-thiodiphosphate) (ADP-beta-s; all 1 x 10-6 1 x 10-3M) evoked only small depolarizations of the vagus nerve, amounting to 47 +/- 2.5%, 40.8 +/- 7.8%, 33.7 +/- 3.3% and 62.4 +/- 12.7% of the response to 5-HT, respectively. Uridine 5'-triphosphate (UTP; 1 X 10-6 1 X 10-3M) was inactive.6. The P2 purinoceptor antagonist, suramin (1 x 10-5-M-1 X 10-4 M), antagonized responses to alpha-beta-methylene ATP. The nature of this antagonism was not, however, consistent with simple competitive kinetics between agonist and antagonist. Depolarizations produced by beta,gamma-methylene ATP and beta,gamma-imido ATP were also attenuated by suramin (1 x 10-4 M), but in contrast, suramin had no effect on responses to ADP, 2-methylthio ATP, ADP-beta-S or 5-HT.7. In addition to its antagonist effects, suramin (10-4 M) markedly increased the maximum amplitude of the depolarization produced by ATP.8. It is concluded that a heterogeneous receptor population mediates depolarization of the rat vagus nerve by purine nucleotides. Importantly, the large amplitude depolarizations to alpha,beta-methylene ATP,beta,gamma-methylene ATP and beta,gamma-imido ATP are mediated via receptors that share many characteristics of the classical P2, receptor. In contrast, the relatively small depolarizing effects of ADP, ADP-beta-S and 2-methylthio ATP were suramin-resistant. Although it appears that other purinoceptors are present,these data suggest that the rat vagus nerve may serve as a useful preparation for studying the pharmacology of neuronal P2x receptors.

Functional characterization of three adenosine receptor types

1. The purpose of the present study was to classify adenosine receptors into A1 and A2 subtypes in a wide range of isolated tissues and cell types (rat adipocytes and atria, guinea-pig ileum and atria (A1); guinea-pig aorta, dog coronary artery and human platelets and neutrophils (A2)) using the R- and S-diastereoisomers of N-phenylisopropyladenosine (PIA), N-cyclopentyladenosine (CPA), the novel compound, N-[(1S,trans)-2-hydroxycyclopentyl]adenosine (GR79236), N-[(2-methylphenyl)methyl]adenosine (metrifudil), 2-(phenylamino)adenosine (CV1808), and 2[[2-[4-(2-carboxyethyl)phenyl]ethyl]amino]-N- ethylcarboxamidoadenosine (CGS21680); N-ethylcarboxamidoadenosine (NECA) was used as a standard. 2. Results obtained in all tissue preparations previously reported to contain A1-receptors could be described by a single rank order of agonist potency: CPA > or = GR79236, R-PIA > or = NECA >> S-PAI > or = metrifudil > or = CV1808, CGS21680. 3. In contrast, two distinct rank orders of agonist potency were observed in preparations previously reported to contain A2-receptors. In dog coronary artery, human neutrophils and platelets the rank order of potency was: CV1808, CGS21680 > or = NECA > R-PIA > or = metrifudil > or = CPA > GR79236 S-PIA. However, in guinea-pig aorta the rank order was: NECA > metrifudil > R-PIA, CPA > CV1808, GR79236 > or = S-PIA, CGS21680. 4. The results of this study are consistent with the existence of three types of adenosine receptor: A1-and two subtypes of A2-receptor. The receptor present in dog coronary artery, human platelets and neutrophils, probably corresponds to the A2a subtype, whilst that present in the guinea-pig aorta may be of the A2b subtype.

Suppression of non-esterified fatty acids and triacylglycerol in experimental animals by the adenosine analogue GR79236

1. This is the first description of the metabolic activity of a novel adenosine A1-receptor agonist, GR79236. GR79236 inhibited catecholamine-induced lipolysis in human, rat and dog isolated adipocytes. 2. Oral administration of GR79236 (0.1-10 mg/kg) to fed rats induced minimal changes in the plasma concentration of non-esterified fatty acids and in the blood concentrations of glucose and lactate. 3. Intravenous infusion of GR79236 to fasted pithed rats, or oral administration of GR79236 to fasted conscious rats and dogs, produced time- and dose-dependent decreases in the plasma non-esterified fatty acid concentration. In the fasted rats, doses of GR79236 that lowered plasma levels of non-esterified fatty acids also produced hypotriglyceridaemia and anti-ketotic effects. 4. Only in the pithed rats were acute effects on the plasma glucose and lactate concentrations observed. Hypoglycaemia and hyperlactataemia occurred over the dose range studied (1 x 10(-11)-1 x 10(-8) mol min-1 kg-1). 5. This profile of activity suggests that compounds such as GR79236 might be agents which can be used to define the role of excessive lipolysis in experimental (and human) pathophysiology.