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Biomedical subjects

J H Lin

Publications and source records attributed to J H Lin.

At least 127 records · Page 7Linked to original sources
PubMed1999

Power Doppler ultrasound imaging in neonatal cerebral venous sinus thrombosis.

Neonatal sinus thrombosis is a rare occurrence in sick neonates. Because of its nonspecific manifestations, the incidence is underestimated. This disease may not be demonstrated by conventional color Doppler and is diagnosed by computed tomography or magnetic resonance imaging. The authors report a neonate with neonatal sinus thrombosis diagnosed by power Doppler and suggest that the technique may be used as a less expensive and more available screening and follow-up method in high-risk neonates.

Female↗
PubMed1999

Dose-dependent plasma clearance of MK-826, a carbapenem antibiotic, arising from concentration-dependent plasma protein binding in rats and monkeys.

After intravenous administration of MK-826, a new carbapenem antibiotic, the compound exhibited nonlinear pharmacokinetics in rats and monkeys. In both species, time-averaged plasma clearance (based on total concentrations) increased about 5-fold over the 10- to 180-mg/kg dose range. MK-826 was extensively plasma protein bound in rat and monkey plasma, and the extent of binding was concentration dependent at plasma concentrations achieved after administration of these doses. Rosenthal analysis of the plasma protein binding indicated that there were two classes of binding sites. The binding capacity of the primary site was comparable to the plasma albumin concentration, which suggested that this primary site consisted of a single site on albumin. The extent of binding of MK-826 to rat albumin was similar to that in whole plasma. Clearance values based on unbound concentrations appeared independent of dose from 10 to 180 mg/kg, which is consistent with saturation of protein binding as the primary cause of the nonlinear pharmacokinetic behavior.

Animals↗
PubMed1999

Central control of blood pressure by nitrergic mechanisms in organum vasculosum laminae terminalis of rat brain.

Experiments were carried out to explore the possible role played by the nitric oxide (NO) system in the organum vasculosum laminae terminalis (OVLT) of rat brain in arterial pressure regulation. Intracerebroventricular (ICV) or intra-OVLT administration of NO donors such as hydroxylamine, sodium nitro-prusside or s-nitro-acetylpenicillamine caused an up to 55 mmHg decrease in blood pressure (BP) but an increase in NO release (measured by porphyrin/nafion coated carbon fibre electrodes in combination with voltammetry) in the OVLT. In contrast, ICV or intra-OVLT administration of N(G)-nitro-L-arginine methyl ester (L-NAME; a constitutive NO synthase inhibitor) caused an up to 45 mmHg increase in BP but a fall in NO release in the OVLT. Compared with the BP responses induced by ICV injection of NO donors or NO synthase inhibitors, the OVLT route of injection required a much lower dose of NO donors or NO synthase inhibitors to produce a similar BP effect. The depressor effects induced by ICV or intra-OVLT administration of NO donors were attenuated by pretreatment with intra-OVLT injection of methylene blue (an inhibitor of guanylate cyclase), haemoglobin (a NO scavenger), L-NAME or spinal transection. On the other hand, the L-NAME-induced pressor effects were attenuated by pretreatment with intra-OVLT injection of L-arginine or spinal transection. The data suggest that activation of cyclic GMP-dependent NO synthase in the OVLT of rat brain causes cyclic GMP-dependent decreases in arterial pressure via inhibiting the sympathetic efferent activity.

Animals↗
PubMed1999

The mechanotransduction of the crayfish stretch receptor neurone can be differentially activated or inactivated by local anaesthetics.

The effect of the local anaesthetics lidocaine, its meta-isomer, LL33, bupivacaine, tetracaine and procaine on the transducer properties of the stretch receptor neurone of the crayfish Pacifastacus leniusculus was investigated using a two microelectrode voltage clamp. Lidocaine increased the receptor current whereas LL33, bupivacaine and tetracaine reduced the receptor current in a reversible dose-dependent way. Procaine did not affect the receptor responses. The onset of the effect was generally slow in the order of minutes. Lidocaine increased the conductance of the mechanotransducer 50 +/- 7% (mean +/- SD, n = 4) and changed the reversal potential -8 +/- 1 mV (mean +/- SEM, n = 8), which indicates a major K+ conductance increase through the mechanosensitive channels. The other local anaesthetics increase the K+ conductance of the mechanotransducer without increasing the total conductance, which suggests that only P(Na)/P(K) is changed. These substances seem to have a Ca2+ dependent effect on the gating properties of the mechanosensitive channels in addition to their effect on the permeability through the channels as compared with lidocaine. All local anaesthetics investigated decreased the leak conductance of the receptor neurone. The effects of local anaesthetics on the mechanosensitive channels whether activating or blocking is correlated to the oil:water distribution coefficients and their relative hydrophobicity/hydrophilicity ratio. The results are consistent with the hypothesis that the local anaesthetic effect is mediated by changes in the lipid phase of the membrane.

Anesthetics, Local↗
PubMed1999

Metabolic interactions between mibefradil and HMG-CoA reductase inhibitors: an in vitro investigation with human liver preparations.

AIMS: To determine the effects of mibefradil on the nletabolism in human liver microsomal preparations of the HMG-CoA reductase inhibitors simvastatin, lovastatin, atorvastatin, cerivastatin and fluvastatin. METHODS: Metabolism of the above five statins (0.5, 5 or 10 microM), as well as of specific CYP3A4/5 and CYP2C8/9 marker substrates, was examined in human liver microsomal preparations in the presence and absence of mibefradil (0.1-50 microM). RESULTS: Mibefradil inhibited, in a concentration-dependent fashion, the metabolism of the four statins (simvastatin, lovastatin, atorvastatin and cerivastatin) known to be substrates for CYP3A. The potency of inhibition was such that the IC50 values (<1 microM) for inhibition of all of the CYP3A substrates fell within the therapeutic plasma concentrations of mibefradil, and was comparable with that of ketoconazole. However, the inhibition by mibefradil, unlike that of ketoconazole, was at least in part mechanism-based. Based on the kinetics of its inhibition of hepatic testosterone 6beta-hydroxylase activity, mibefradil was judged to be a powerful mechanism-based inhibitor of CYP3A4/5, with values for Kinactivation, Ki and partition ratio (moles of mibefradil metabolized per moles of enzyme inactivated) of 0.4 min(-1), 2.3 microM and 1.7, respectively. In contrast to the results with substrates of CYP3A, metabolism of fluvastatin, a substrate of CYP2C8/9, and the hydroxylation of tolbutamide, a functional probe for CYP2C8/9, were not inhibited by mibefradil. CONCLUSION: Mibefradil, at therapeutically relevant concentrations, strongly suppressed the metabolism in human liver microsomes of simvastatin, lovastatin, atorvastatin and cerivastatin through its inhibitory effects on CYP3A4/5, while the effects of mibefradil on fluvastatin, a substrate for CYP2C8/9, were minimal in this system. Since mibefradil is a potent mechanism-based inhibitor of CYP3A4/5, it is anticipated that clinically significant drug-drug interactions will likely ensue when mibefradil is coadministered with agents which are cleared primarily by CYP3A-mediated pathways.

Aryl Hydrocarbon Hydroxylases↗
PubMed1999

Microcalcifications of non-palpable breast lesions detected by ultrasonography: correlation with mammography and histopathology.

OBJECTIVES: Microcalcifications are generally not demonstrated well on ultrasonography. In this study, we attempted to demonstrate the usefulness of high-resolution ultrasonography in the detection of microcalcifications associated with non-palpable breast cancers. DESIGN: Fourteen patients with non-palpable breast lesions in whom microcalcifications were detected or suspected by ultrasonography and one patient in whom microcalcifications were detected on mammography only were included in the study. Mammography and analysis of biopsy specimens were performed in each patient and the findings were correlated with the ultrasonographic findings. Ultrasonography and mammography were performed independently by different physicians at different times. RESULTS: In three patients < or = 30 years of age, who were not at high risk of breast cancer and who had no evidence of cancer on palpation, high-resolution ultrasonography clearly showed microcalcifications but no mass. Two of these patients had ductal carcinoma in situ and one had small invasive carcinoma with extensive comedocarcinoma. Among the other 12 patients with non-palpable breast lesions, ultrasonography detected microcalcifications accurately in six and suggested possible microcalcifications in a further four. Microcalcifications in all of these ten patients were confirmed by mammography thereafter. Four of these ten patients had ductal carcinoma in situ, with or without invasive carcinoma. Of the remaining two patients, one demonstrated false-positive findings and one false-negative findings on ultrasound. On high-resolution ultrasonography, microcalcifications produced the appearance of twinkling stars (bright dots in different planes) in a dark sky (contrasted against ill-defined hypoechoic patches), corresponding on histopathology to groups of expanded ducts with increased cell density with or without necrosis. CONCLUSION: High-resolution ultrasonography may be used for detection of microcalcifications in non-palpable breast lesions. Ultrasonography is helpful in screening for early breast cancers, especially in young patients who are at risk for breast cancer and in whom mammography is not usually carried out.

Adult↗
PubMed1999

p50(cdc37) acting in concert with Hsp90 is required for Raf-1 function.

Genetic screens in Drosophila have identified p50(cdc37) to be an essential component of the sevenless receptor/mitogen-activated kinase protein (MAPK) signaling pathway, but neither the function nor the target of p50(cdc37) in this pathway has been defined. In this study, we examined the role of p50(cdc37) and its Hsp90 chaperone partner in Raf/Mek/MAPK signaling biochemically. We found that coexpression of wild-type p50(cdc37) with Raf-1 resulted in robust and dose-dependent activation of Raf-1 in Sf9 cells. In addition, p50(cdc37) greatly potentiated v-Src-mediated Raf-1 activation. Moreover, we found that p50(cdc37) is the primary determinant of Hsp90 recruitment to Raf-1. Overexpression of a p50(cdc37) mutant which is unable to recruit Hsp90 into the Raf-1 complex inhibited Raf-1 and MAPK activation by growth factors. Similarly, pretreatment with geldanamycin (GA), an Hsp90-specific inhibitor, prevented both the association of Raf-1 with the p50(cdc37)-Hsp90 heterodimer and Raf-1 kinase activation by serum. Activation of Raf-1 via baculovirus coexpression with oncogenic Src or Ras in Sf9 cells was also strongly inhibited by dominant negative p50(cdc37) or by GA. Thus, formation of a ternary Raf-1-p50(cdc37)-Hsp90 complex is crucial for Raf-1 activity and MAPK pathway signaling. These results provide the first biochemical evidence for the requirement of the p50(cdc37)-Hsp90 complex in protein kinase regulation and for Raf-1 function in particular.

Animals↗
PubMed1999

The influence of rehabilitation therapy on the prognosis for stroke patients--a preliminary study.

The purpose of this prospective study was to investigate the influence of rehabilitation therapy on the prognosis for stroke patients. Sociodemographic and clinical factors were collected in a sample of 147 stroke patients (81 men and 66 women) admitted to the inpatient rehabilitation department at our university hospital over 10 days between January 1, 1997 and December 31, 1997. Functional Independence Measure (FIM) scores at discharge and gains during rehabilitation period were used as the prognosis index. Statistical techniques with univariate and multiple regression analyses indicated that significant predictors of discharge FIM scores include age, previous attacks twice or over, medical comorbidities, sensory and orientation impairments, and dementia. In addition, previous stroke attacks twice or over and sensory impairment were significant predictors of FIM gains during rehabilitation period. We concluded that: 1) age is a critical factor to determine the rehabilitation outcome, but may not be an important factor to predict the ability for the improvement through rehabilitation therapy; 2) the delay of rehabilitation therapy may not affect the potential for further improvement; 3) patients with low initial functional level may have poor final outcome, they may still have good rehabilitation potential to improve the functional level; 4) complications of stroke may affect the rehabilitation outcome and should be prevented; and 5) patients with impaired mental status should not routinely be excluded from rehabilitation programs.

Adult↗
PubMed1999

Statistical method for characterization of hypertrophic cardiomyopathy by use of morphologic and pathologic measurements in pigs (Sus scrofa domestica).

BACKGROUND AND PURPOSE: Hypertrophic cardiomyopathy (HCM) is characterized by symmetric or asymmetric hypertrophy of the left and/or right ventricle. Morphologic and pathologic indices (MI and PI) of hearts were established for classification of HCM in pigs. METHODS: Fifty on-farm-performance-tested pigs (average body weight, 104.3 kg; age, 224.5 days) were randomly selected. Heart weight, length, width, heart-to-body weight ratio, and thickness of the cranial and middle portions of ventricular septum and left ventricular free wall were measured. Myocyte disorganization and necrosis, myocardial and endocardial fibrosis, and intramural coronary arterial occlusion were scored. Principal component analysis and stepwise regression analysis were used to establish MI and PI. RESULTS: MI was established by using the first principal component as the dependent variable and applying stepwise regression analysis. Hearts were classified as morphologically normal, suspicious, and hypertrophic according to the range of MI. The same statistical method was used to find PI. Hearts were classified as pathologically normal, moderately affected, or seriously affected according to the range of PI. Combining MI and PI, hearts could be classified into five groups: no hypertrophy with minor lesion (normal); hypertrophy but with rare lesion; no hypertrophy but seriously affected; suspicious; and hypertrophy and seriously affected (heart with HCM). Another 119 hearts were collected and classified. The variation of heart measurements was consistent with the original purpose of classification. CONCLUSIONS: Using fewer measurements for identification of HCM objectively in pigs seems to have practical application.

Animals↗
PubMed1999

Modulation of rat cytochrome P-450 by an investigational HIV protease inhibitor.

Previous studies in vitro have revealed that L-754,394, an HIV protease inhibitor, is a potent suicide inhibitor of cytochrome P-450 enzymes. The present report examines the effect of chronic treatment of L-754,394 on hepatic cytochrome P-450s in adult male rats. L-754,394 was administered orally once a day for 7 days and resulted in significant changes in marker activities. An unusual parabolic (ascending, then descending) profile was observed for testosterone 2beta-/6beta-(CYP 3A1/2-catalyzed) hydroxylase activities during the 7-day treatment with 20 mg/kg L-754,394. These activities, which were elevated 2-fold on day 2, returned to basal levels by day 8. In contrast, testosterone 2alpha-/16alpha-(CYP2C11-catalyzed) hydroxylase activities showed an opposite parabolic (descending, then ascending) profile during the same period, reducing to 40% of control activities on day 4, followed by a rebounding trend. Immunoquantitation of CYP 3A1/2 and 2C11 showed that the expressed protein levels were in parallel with the associated activities. Furthermore, mRNA levels of CYP 3A2 and CYP2C11 showed the same trends as the protein expression of the respective isoforms. These observations show that L-754,394 perturbs the relative abundance of P-450 isoforms in rat liver by affecting the regulation at a pretranslational step. This may further involve a disturbance of hormonal homeostasis. Although serum levels of testosterone did not show a marked change during treatment, thyroxine and triiodothyronine markedly decreased on days 2 and 4, and subsequently increased to basal levels.

Animals↗
PubMed1999

Effect of dexamethasone on the intestinal first-pass metabolism of indinavir in rats: evidence of cytochrome P-450 3A [correction of P-450 A] and p-glycoprotein induction .

Indinavir, a potent and specific inhibitor of HIV protease, is a known substrate of cytochrome P-450 (CYP) 3A and p-glycoprotein. The purpose of this study is to investigate and compare the inducing effect of dexamethasone (DEX) on CYP3A and p-glycoprotein in the hepatic and intestinal first-pass metabolism of indinavir in rats. Pretreatment of rats with DEX had little effect on the pharmacokinetics (Cl and T(1/2)) after i.v. administration of indinavir, whereas DEX markedly altered the peak concentration (C(max)) and bioavailability of indinavir after oral dosing. The C(max) decreased from 2.8 microM in control rats to 0.28 microM in DEX-treated rats, and bioavailability decreased from 28 to 12.4%. The decreased bioavailability after DEX pretreatment was due mainly to an increase in first-pass metabolism. Intestinal first-pass metabolism (E(G)) increased from 6% in control rats to 34% in DEX-treated rats, and hepatic first-pass metabolism (E(H)) increased from 65 to 82%. Analysis of in vitro kinetic data revealed that the increased intestinal and hepatic metabolism by DEX was attributed to an increase in the V(max), as a result of CYP3A induction, without a significant change in the K(m) values. DEX pretreatment also induced p-glycoprotein in the intestine and liver of rats. p-Glycoprotein appeared to increase the intestinal metabolism of indinavir whereas it had little effect on the hepatic metabolism of indinavir. Although it has been suggested that the role of intestinal metabolism for some drugs is quantitatively greater than that of hepatic metabolism in the overall first-pass metabolism, the contribution of intestinal metabolism to the overall first-pass metabolism of indinavir in rats is not quantitatively as important as the hepatic metabolism, regardless of DEX induction.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

The relation between admission balance and functional outcomes following stroke rehabilitation: a medical center based study.

This prospective study evaluated the clinical use of the Fugl-Meyer Balance Scale (FMBS) on stroke patients during hospitalization and assessed the relationship between balance score at admission to the rehabilitation program and functional outcome at discharge. One hundred and sixty-three stroke patients admitted to the in-patient rehabilitation department of a university-based medical center between January 1 and December 31, 1997 were recruited for this investigation. Functional ability was evaluated with the Functional Independence Measure (FIM) instrument, and balance was measured using the 7-item Fugl-Meyer Balance Scale. These measures were assessed both at admission to and discharge from the inpatient rehabilitation program. Pearson correlation and multiple regression analyses were used to determine the relationship between balance and functional ability scores at admission and rehabilitation outcomes at discharge, including length of stay, functional gain, and efficiency. The results demonstrated that the balance score at admission accounted for 6% of the variation in length of stay, once demographic influences were controlled. The FIM efficiency score could possibly be predicted by the balance ability at admission, which accounted for 3% of the variance. However, the balance score could not provide predictive information about the FIM gain beyond that already provided by the FIM score at admission, which accounted for 4% of the variance with demographic factors controlled. Overall, balance ability at admission, assessed by the Fugl-Meyer Balance Scale, had no or at least only little, contribution to account for the variance in rehabilitation outcomes. These findings suggest that the use of Fugl-Meyer Balance Scale at admission to stroke inpatient rehabilitation seemed not to enhance the ability to predict rehabilitation outcomes.

Adult↗
PubMed1999

Sequential Doppler sonographic studies of embolization in a patient with hepatic involvement in hereditary hemorrhagic telangiectasia: correlation with angiographic findings.

A 41-year-old man was admitted for symptoms of progressive congestive heart failure. His family history and the results of a physical examination were highly suggestive of Osler-Weber-Rendu disease (hereditary hemorrhagic telangiectasia, HHT). Cardiac catheterization and hepatic angiography demonstrated HHT with left-to-right shunting from the liver. The patient underwent transcatheter arterial embolization (TAE) of the right hepatic artery. We performed both Doppler sonography and angiography before and after TAE. The treatment improved the clinical manifestations of congestive heart failure, including the edema of the leg and dyspnea. Doppler sonographic studies also showed an increased resistive index in the right hepatic artery and decreased flow volumes and velocities in the right and middle hepatic veins, respectively, after treatment. Corresponding changes on angiography after TAE showed decreased right hepatic arterial flow and nonopacified branches distal to the coils, disappearance of the mottled hepatogram in the right lobe, reduction of contrast agent staining, and enhanced calibers in the right and middle hepatic veins. This case illustrates that qualitative and quantitative studies with duplex and color Doppler ultrasound can be used to detect or define the extent of hepatic involvement in HHT patients before TAE, monitor hemodynamic changes of the intrahepatic vasculature after TAE, evaluate the efficacy of treatment, and possibly obviate the need for repeated angiography for diagnosis only.

Adult↗
PubMed1999

Interaction of diclofenac and quinidine in monkeys: stimulation of diclofenac metabolism.

The cytochrome P-450 (CYP)3A4-mediated metabolism of diclofenac is stimulated in vitro by quinidine. A similar effect is observed in incubations with monkey liver microsomes. We describe an in vivo interaction of diclofenac and quinidine that leads to enhanced clearance of diclofenac in monkeys. After a dose of diclofenac via portal vein infusion at 0.055 mg/kg/h, steady-state systemic plasma drug concentrations in three male rhesus monkeys were 87, 104, and 32 ng/ml, respectively (control). When diclofenac was coadministered with quinidine (0.25 mg/kg/h) via the same route, the corresponding plasma diclofenac concentrations were 50, 59, and 18 ng/ml, representing 57, 56, and 56% of control values, respectively. In contrast, steady-state systemic diclofenac concentrations in the same three monkeys were elevated 1.4 to 2.5 times when the monkeys were pretreated with L-754,394 (10 mg/kg i.v.), an inhibitor of CYP3A. Further investigation indicated that the plasma protein binding (>99%) and blood/plasma ratio (0.7) of diclofenac remained unchanged in the presence of quinidine. Therefore, the decreases in plasma concentrations of diclofenac after a combined dose of diclofenac and quinidine are taken to reflect increased hepatic clearance of the drug, presumably resulting from the stimulation of CYP3A-catalyzed oxidative metabolism. Consistent with this proposed mechanism, a 2-fold increase in the formation of 5-hydroxydiclofenac derivatives was observed in monkey hepatocyte suspensions containing diclofenac and quinidine. Stimulation of diclofenac metabolism by quinidine was diminished when monkey liver microsomes were pretreated with antibodies against CYP3A. Subsequent kinetic studies indicated that the K(m) value for the CYP-mediated conversion of diclofenac to its 5-hydroxy derivatives was little changed (75 versus 59 microM), whereas V(max) increased 2.5-fold in the presence of quinidine. These data suggest that the catalytic capacity of monkey hepatic CYP3A toward diclofenac metabolism is enhanced by quinidine.

Animals↗
PubMed1999

Pharmacokinetics of alendronate: an overview.

Alendronate (4-amino-1-hydroxybutylidene-1,1-bisphosphonate, MK-217, Fosamax), an aminobisphosphonate, is a potent inhibitor of osteoclast-mediated bone resorption and is used for the treatment of bone disorders, osteoporosis and Pagets disease of bone. Alendronate, like all bisphosphonates, is absorbed poorly in animals and humans; oral bioavailability is less than 2% in all species studied, including humans. Systemically available alendronate disappears very rapidly from plasma, and the drug is either taken up by bone tissues or excreted by the kidneys. Renal excretion is the only route of elimination, and urinary recovery is similar among species, ranging from 30% to 50% in a 24-hour collection period. Studies in rats show that alendronate is actively secreted by an uncharacterised renal transport system, but not by anionic or cationic renal transport systems. Drug not excreted within 24 hours after dosing is believed to be sequestered in the skeleton, from which it is liberated slowly into the circulation to be eliminated renally. Once taken up by the bone, the elimination of alendronate from bone tissue is slow, ranging from 200 days in rats, 3 years in dogs and 12 years in humans. The phamacokinetics and unique targeting of alendronate to bone contribute to the utility of this drug for the management of skeletal disorders.

Absorption↗
PubMed1999

Nonlinear pharmacokinetics of efavirenz (DMP-266), a potent HIV-1 reverse transcriptase inhibitor, in rats and monkeys.

Efavirenz (EFV, Sustiva, Stocrin, DMP-266, L-743,726) is a potent and selective non-nucleoside inhibitor of HIV-1 reverse transcriptase. Pharmacokinetics of EFV was studied in rats and monkeys, the safety assessment species. In rats, after 2 and 5 mg/kg i.v. administrations, the mean CLp, Vdss, and T1/2 were 67 ml/min/kg, 5.0 liters/kg, and 1 h, respectively. EFV was metabolized completely, and the products were excreted almost exclusively via bile. At the higher dose of 15 mg/kg, the CLp was reduced by 36%, implying saturation of metabolism processes. A similar phenomenon occurred in monkeys, where the CLp declined by 60% as the i.v. dose was increased from 5 to 15 mg/kg. After oral dosing, the bioavailability of EFV in rats (10 mg/kg) and monkeys (2 mg/kg) was 16% and 42%, respectively. Higher doses in both species led to disproportionate increases in the AUC and higher Tmax values, suggesting saturation of metabolism and/or prolongation of absorption. The delay in Tmax was more pronounced in monkeys where the plasma concentrations reached plateaus and were sustained for 4 to 20 h. In rats, the prolongation of absorption was due to delayed gastric emptying as demonstrated by >10-fold slower transit of [14C]polyethylene glycol through the stomach of EFV-pretreated animals. The delayed gastric emptying in monkeys also was observed when the animals dosed at 160 mg/kg exhibited emesis, 8 h postdose, which was found to contain a substantial portion of the dose. These results demonstrated that in rats and monkeys, both delayed gastric emptying and saturation of metabolic processes played significant roles in the nonlinear pharmacokinetics of EFV.

Alkynes↗
PubMed1998

Connexins regulate calcium signaling by controlling ATP release.

Forced expression of gap junction proteins, connexins, enables gap junction-deficient cell lines to propagate intercellular calcium waves. Here, we show that ATP secretion from the poorly coupled cell lines, C6 glioma, HeLa, and U373 glioblastoma, is potentiated 5- to 15-fold by connexin expression. ATP release required purinergic receptor-activated intracellular Ca2+ mobilization and was inhibited by Cl- channel blockers. Calcium wave propagation also was reduced by purinergic receptor antagonists and by Cl- channel blockers but insensitive to gap junction inhibitors. These observations suggest that cell-to-cell signaling associated with connexin expression results from enhanced ATP release and not, as previously believed, from an increase in intercellular coupling.

Adenosine Triphosphatases↗