Effect of ACL reconstruction tunnels on stress in the distal femur.

PURPOSE: This study examined the change in femoral stress caused by graft tunnels drilled for anterior cruciate ligament (ACL) reconstruction. Using a computational model, the number, geometry and position of the graft tunnels exits were varied to determine the effect on bone stress. METHODS: A finite element model of the distal femur was developed from a CT scan of a cadaveric knee. To assess the model, the strain calculated computationally was compared to experimentally measured strains in eleven unpaired human cadaver femurs. Using the computational model, the number, geometry and position of the graft tunnel exits were varied to determine the effect on bone stress based on the stress concentration factor: the ratio of bone stress with tunnels to intact bone stress. RESULTS: The results indicated that the second tunnel in double-bundle ACL reconstruction results in approximately a 20 % increase in the maximum femoral stress as compared to single-bundle reconstruction. The highest stresses occur at the tunnel exits. The position of the tunnel exits effects femoral stress with the stress increasing slightly (AM SCR from 0.7 to 1 and PL SCR from 1.2 to 1.3) when the AM tunnel exit is moved anteriorly and having greater increases as the posterior lateral (PL) tunnel exit is moved laterally (PL SCR from 1.2 to 1.7) or posteriorly (PL SCR from 1.2 to 2). CONCLUSION: In anatomical ACL reconstruction, the tunnel entrances are dictated by anatomy; however, there can be variations in tunnel exit positions. Consideration should be given when positioning tunnel exits on the effect on stress in the femur. Moving the PL tunnel exit laterally or posteriorly increases in the stress at the PL tunnel exit.

Echolocation and pursuit of prey by bats.

Echolocating bats use different information-gathering strategies for hunting prey in open, uncluttered environments, in relatively open environments with some obstacles, and in densely cluttered environments. These situations differ in the extent to which individual targets such as flying insects can be detected as isolated objects or must be separated perceptually from backgrounds. Echolocating bats also differ in whether they use high-resolution, multidimensional images of targets or concentrate specifically on one particular target dimension, such as movement, to detect prey.

Different contributions of voltage-sensitive Ca2+ channels to histamine-induced catecholamine release and tyrosine hydroxylase activation in bovine adrenal chromaffin cells.

Histamine stimulates catecholamine release and tyrosine hydroxylase activity in a Ca(2+)-dependent manner in bovine adrenal chromaffin cells. The role of voltage-sensitive Ca2+ channels in these two responses has been investigated. Using an EC50 concentration of histamine, 1 microM, catecholamine release was enhanced by (+/-)BayK8644, and partially inhibited by nitrendipine and omega-agatoxin IVA, blockers of L- and P/Q-type Ca2+ channels. omega-Conotoxin GVIA gave small and variable inhibitory effects. With a maximal histamine concentration, 10 microM, similar results were obtained except that now omega-conotoxin GVIA reliably reduced release. In contrast, neither (+/-)BayK8644 nor any of the individual Ca2+ channel antagonists had any significant effect on tyrosine hydroxylase (TOH) activation induced by either an EC50 or a maximal concentration of histamine. When high concentrations of nitrendipine, omega-conotoxin GVIA and omega-agatoxin IVA were combined with omega-conotoxin MVIIC (a non-selective blocker of N, P and Q channels) to block voltage-sensitive Ca2+ channels in these cells, release induced by K+ depolarization was completely blocked. Release caused by histamine, however, was substantially reduced but not abolished. The combination of antagonists also only partially inhibited TOH activation by histamine. The results show that the G protein-coupled receptor agonist histamine activates several different types of voltage-sensitive Ca2+ channels in chromaffin cells to mediate its cellular effects. Histamine may also activate additional pathways for Ca2+ entry. The results also suggest that the manner by which Ca2+ controls release and TOH activation once it has entered chromaffin cells through these channels are different.

Metabolic turnover of proliferation-related nuclear proteins in serum-stimulated Swiss mouse 3T3 cells.

Stimulation of quiescent Swiss mouse 3T3 cells either by serum or by pure growth factors induces DNA synthesis after a lag period of about 15 h. Following restimulation by serum or by growth factors there is an overall increase of 2-4-fold in the rate of biosynthesis of nuclear proteins. Two nuclear polypeptides show specific temporal correlations with the transition from quiescence to proliferation. The synthesis of p30 (30 kDa, pI 5.2) is at a maximum within 5 h of restimulation, while the synthesis of p36 (36 kDa, pI 4.25) is first seen at 10-12 h after restimulation. The synthesis of p36 correlates well with the initiation of DNA biosynthesis. The metabolic turnover of both of these proteins has been estimated by pulse-chase and by cycloheximide inhibition experiments. They both have a half-life of 10-15 h and appear to be cell-cycle related.

ADP-ribosylation reactions in plants.

Poly ADP-ribosylation is a post-translational modification of protein structure and function that occurs in the nucleus of most eukaryotic cells. Although its function has not been fully elucidated it is thought to have a role in the processing DNA strand breaks. Poly(ADP-ribose) polymerase, a highly conserved enzyme, is well studied in animal cell systems but is less well characterised in plants. Our present understanding of mono and poly ADP-ribosylation reactions in plants is reviewed in this article.

Effects of N- and L-type calcium channel antagonists and (+/-)-Bay K8644 on nerve-induced catecholamine secretion from bovine perfused adrenal glands.

1. The effects of N- and L-type calcium channel antagonists and (+/-)-Bay K8644 on catecholamine release from chromaffin cells and acetylcholine release from splanchnic nerve terminals was investigated in bovine perfused adrenal glands. 2. Adrenal glands were perfused retrogradely and preloaded with [3H]-choline. Subsequent efflux of 3H-labelled compounds was taken as an index of acetylcholine release from the splanchnic nerve terminals. Noradrenaline and adrenaline release from the glands was measured by h.p.l.c. with electrochemical detection. 3. A maximally effective frequency of field stimulation of the adrenal nerves, 10 Hz, induced release of catecholamines and 3H-labelled compounds. Tetrodotoxin (1 microM) abolished release of both catecholamines and 3H-labelled compounds. A combination of mecamylamine (5 microM) and atropine (1 microM) inhibited nerve-induced catecholamine release by about 75% but did not inhibit release of 3H-labelled compounds. Reducing the concentration of extracellular calcium 5 fold to 0.5 mM inhibited nerve-induced catecholamine release by 80% and release of 3H-labelled compounds by 50%. 4. (+/-)-Bay K8644 (1 microM), nitrendipine (1 microM), omega-conotoxin-GVIA (10 nM) and the combination of nitrendipine and omega-conotoxin-GVIA each had no effect on nerve-induced release of 3H-labelled compounds. 5. (+/-)-Bay K8644 (1 microM) potentiated nerve-induced catecholamine release by 75%. Nitrendipine (1 microM) reduced release by 20% but this did not reach statistical significance, omega-Conotoxin-GVIA (10 nM) reduced nerve-induced catecholamine release by 75%, while the combination of omega-conotoxin-GVIA and nitrendipine reduced release to the same extent as omega-conotoxin-GVIA alone. 6. Exogenous acetylcholine perfusion through the glands produced a concentration-dependent increase in catecholamine release. The maximally effective concentration of acetylcholine for catecholamine release was > or = 300 microM, while 30 microM acetylcholine gave comparable catecholamine release to that obtained with 10 Hz field stimulation. 7. (+/-)-Bay K8644 (1 microM), nitrendipine (1 microM) and omega-conotoxin-GVIA (10 nM) each had no significant effect on catecholamine release evoked by perfusion of the gland with either a near maximally effective concentration of acetylcholine, 100 microM, or with the lower concentration of 30 microM. 8. The results show that the omega-conotoxin-GVIA-sensitive N-type voltage-sensitive calcium channels located on the chromaffin cells are largely responsible for catecholamine release induced by nerve stimulation in bovine adrenal glands. In contrast, N-type calcium channels are not involved in catecholamine release induced by exogenous acetylcholine. L-type voltage sensitive calcium channels do not play a major role in nerve-induced or exogenously applied acetylcholine-induced catecholamine release. However, the L-type calcium channels do have the potential to augment powerfully nerve-induced catecholamine release. N- and L-type calcium channels do not play a major role in the presynaptic release of acetylcholine.

Multiple calcium channels are required for pituitary adenylate cyclase-activating polypeptide-induced catecholamine secretion from bovine cultured adrenal chromaffin cells.

The effects of L-, N-, P- and Q-type calcium channel antagonists and (+/-)-BayK-8644 on catecholamine release induced by pituitary adenylate cyclase-activating polypeptide (PACAP-27) were investigated in bovine cultured adrenal chromaffin cells. PACAP-27 induced the release of 4-15% of the total cellular catecholamines over 7 min, with an EC50 of 20 nM and the effect approaching maximum at 100 nM. Catecholamine release was fully dependent on the presence of extracellular calcium. The dihydropyridine nitrendipine which inhibits L-type calcium channels inhibited PACAP-27-induced secretion in a concentration dependent manner with an inhibition of 20-30% at 1 microM. In contrast, (+/-)-BayK-8644, which prolongs the opening of L-type calcium channels produced a concentration-dependent increase in PACAP-27-induced catecholamine release with 1 microM increasing release by 40-60%. Blockade of N-type calcium channels with omega-conotoxin GVIA reduced release by 5-15%. Block of P-type channels with low concentrations of omega-agatoxin IVA (< or = 30 nM) had no significant effect on release, while higher concentrations (100-300 nM) which block Q-type channels reduced release by up to 15%. omega-Conotoxin MVIIC, an antagonist of Q-type calcium channels and also of N- and P-type channels, inhibited release in a concentration-dependent manner with a near maximum effect of 30-50% produced by 300 nM. The combination of omega-conotoxin GVIA and omega-agatoxin IVA reduced release by 40-50%. Addition of omega-conotoxin MVIIC (300 nM) to the combination of omega-conotoxin GVIA (10 nM) and omega-agatoxin IVA (100 nM) did not inhibit catecholamine release more than with omega-conotoxin GVIA and omega-agatoxin IVA alone, indicating that 100 nM omega-agatoxin IVA was sufficient to block the Q-type calcium channels. When nitrendipine was used together with omega-conotoxin GVIA, omega-agatoxin IVA and omega-conotoxin MVIIC, catecholamine release induced by 20 nM or 100 nM PACAP-27 was reduced by 70-85%. Taken together these results suggest that influx of calcium through multiple different voltage-sensitive calcium channels mediate PACAP-27-induced catecholamine release from bovine chromaffin cells, and that L-, N- and Q-channels contribute to this response.

Caffeine enhances sympathetic purinergic and noradrenergic transmission in the guinea-pig isolated vas deferens.

Intracellular recording techniques were used to monitor the resting membrane potential of smooth muscle cells and the excitatory junction potentials (EJPs) evoked by stimulation of the hypogastric nerve. Stimulation with trains of 15 pulses at 1 Hz or 0.33 Hz evoked individual EJPs which increased in amplitude from the first pulse and reached a plateau after 6-8 pulses. Stimulation at 1 Hz resulted in EJPs facilitating to a plateau level of approximately 25 mV, whereas with stimulation at 0.33 Hz the EJPs only facilitated to a plateau level of about 12 mV. With stimulation at 1 Hz, caffeine (3 mM and 10 mM), increased the amplitude of the first few EJPs in each train and decreased the extent of facilitation and reduced the amplitude of fully facilitated EJPs. In comparison, the amplitude of all EJPs evoked by stimulation at 0.33 Hz was increased by caffeine (3 mM and 10 mM). With 0.33 Hz stimulation, facilitation of the first few EJPs was observed in the presence of 3 mM caffeine but not in the presence of 10 mM caffeine. In the presence of the alpha 2-adrenoceptor antagonist idazoxan, caffeine (3 mM and 10 mM) still enhanced the amplitude of EJPs early in trains of stimulation but there was no depression of EJPs later in the trains. Similarly, in reserpine-treated vasa deferentia, caffeine (3 mM) enhanced EJPs early in the train of stimulation at 1 Hz and there was no depression of EJPs at the end of the train. In addition to electrophysiological experiments, the effect of caffeine (0.1-30 mM) on the resting and stimulation-induced (S-I) efflux of radioactivity was investigated in guinea-pig isolated vasa deferentia previously incubated with [3H]-noradrenaline. Caffeine (10 mM) did not affect the resting efflux of [3H]-noradrenaline but significantly enhanced the S-I efflux by 150-160%. The present findings suggest that caffeine enhances sympathetic purinergic and noradrenergic transmission at the sympathetic neuroeffector junction in the guinea-pig vas deferens. Moreover, the increased release of transmitter noradrenaline can modulate purinergic transmission by activation of alpha 2-adrenoceptors located at sympathetic neuroeffector sites.

Studies on the mechanism of enhancement of purinergic transmission by caffeine in the guinea-pig isolated vas deferens.

1. Purinergic transmission from sympathetic nerves in the guinea-pig vas deferens was monitored using intracellular recording techniques. Stimulation of the hypogastric nerve with trains of 15 pulses at 1 Hz evoked excitatory junction potentials (EJPs) which increased in amplitude from the first pulse and reached a maximum after 6-8 pulses. 2. Caffeine (3 and 10 mm), depolarized cells by 5-10 mV and increased the amplitude of the first few EJPs in each train but reduced the maximum amplitude of EJPs late in the train. 3. The adenosine receptor antagonist 8-p-sulphophenyl-theophylline (8-SPT; 30 microm) had no effect on either the resting membrane potential or the EJP amplitude; however, at 100 microm it reduced the amplitude of all EJPs by 5-10%. 4. Adenosine (10 and 30 microm) reduced the amplitude of EJPs in a concentration-dependent manner. The inhibitory effect of adenosine on EJP amplitude was prevented by pretreatment with either caffeine (3 mm) or 8-SPT (30 microm). 5. Ryanodine (30 microm) did not alter EJP amplitude and did not inhibit the enhancement of the first EJP by caffeine (3 mm). Incubation of the tissue with the cell permeable calcium chelator 1-2-bis(o-aminophenoxy)ethane-N,N-N',N'-tetraacetic acid (BAPT-AM) resulted in a depression of EJP amplitude and a longer time to reach maximum amplitude. In cells that had been exposed to BAPT-AM, caffeine 3 mm still increased amplitude of EJP early in the train. 6. The phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX; 500 microm), hyperpolarized cells and increased the amplitude of EJP throughout the train of stimulation. In the presence of IBMX, caffeine 3 mm still depolarized the cells and enhanced the EJP early in the train of stimulation. 7. The findings in this study confirm that caffeine and 8-SPT are effective inhibitors of the actions of adenosine. However, caffeine has an additional action to enhance EJP early during a train of stimulation, which cannot be attributed to blockade of adenosine receptors, but which may be related to inhibition of phosphodiesterase.

Evaluation of a community fissure sealant programme in County Meath, Ireland.

OBJECTIVE: To evaluate the fissure sealant programme operated by the North Eastern Health Board Dental Service in County Meath, Republic of Ireland. The fissure sealant programme forms part of the school dental service aimed at children in first class (age group 6-7 years). DESIGN: Cross sectional study with retrospective analysis of dental records. CLINICAL SETTING: Schools in County Meath in 1999. PARTICIPANTS: Children in fourth class (mean age 9.6 years) in the school year 1999/2000 who had participated in the fissure sealant programme in the school year 1996/97. MAIN OUTCOME MEASURES: Sealant retention using the criteria of Simonsen. RESULTS: The mean age of sealant was 2.3 years. Fifty six percent of sealants were completely retained, 27% were partially retained and 12.8% were missing. The majority (73%) of children had some sealant on at least one tooth. Caries experience in previously sealed teeth was low (2.9%). Children who had all four first permanent molars sealed had a significantly lower DMFT (visual) than those who had no sealants (Wilcoxan p < 0.0001). CONCLUSION: Despite lack of maintenance of sealants in this study, retention rates compared favourably with similar international studies and caries experience in previously sealed teeth was low. The use of a written sealant policy and protocol for sealant application and equipment maintenance could further improve retention rates. Children who had no sealants had significantly poorer dental health than children who had all four first permanent molars sealed.

Dental health and treatment needs among a sample of Bangladeshi medical users aged 40 years and over living in Tower Hamlets, UK.

AIM: To assess the dental health status and treatment needs of Bangladeshi medical care users aged 40 years and over and to explore the relationship of oral disease status, tobacco usage and paan (betel quid) chewing. DESIGN: Multi-centre cross-sectional study. SETTING: General medical practitioners' waiting areas in Tower Hamlets, UK. SUBJECTS: 185 Bangladeshi adults aged 40 years and over. INTERVENTION: A clinical examination and an interview schedule. MEASURES: Dental status, periodontal status, dental plaque, calculus and denture status. Tobacco smoking and paan chewing behaviour. RESULTS: The response rate was 74%. 85% of participants were dentate with an average number of 24 (SD +/- 5.4) standing teeth. The mean DMFT score was 5.38, with missing teeth (3.81) being the major component. The decayed component was 0.43 and the filled was 1.14. 46% of participants were assessed as being free from gingivitis. Significant relationships between chewing paan and aspects of dental and periodontal status were found. Impacts of oral health were reported by 45% of the respondents. The normative need for dental treatment was 96% with a perceived need of 48%. CONCLUSION: There was considerable normative dental need. Whilst caries experience was low, there were high levels of periodontal treatment needs. Paan chewing was related to aspects of dental and periodontal status.

Prevalence of oral lesions among a sample of Bangladeshi medical users aged 40 years and over living in Tower Hamlets, UK.

AIM: To collect data on the prevalence of oral mucosal lesions among Bangladeshi medical care users aged 40 years and over and to explore the relationship of oral disease status and tobacco smoking and paan (betel quid) chewing. DESIGN: Multi-centre cross-sectional study. SETTING: General medical practitioners' waiting areas in Tower Hamlets, UK. SUBJECTS: 185 Bangladeshi adults aged 40 years old and over. METHOD: An oral mucosal examination, based on WHO criteria and an interview. Information on tobacco smoking and paan chewing behaviour was collected during the interview. RESULTS: Out of 185 adults there was a response rate of 74%. Oral mucosal lesions were observed in 40% of participants. The most common lesion was found to be leukoplakia with a prevalence of 25%. Significant relationships were found between smoking and the presence of oral pathology and between paan chewing with tobacco and the presence of leukoplakia. CONCLUSION: In this study of older Bangladeshi medical care users there was a high prevalence of oral mucosal lesions. Sensitively tailored health promotion interventions, which aim to reduce tobacco use, should be developed for this population.

The prevalence of dental erosion in the maxillary incisors of 14-year-old schoolchildren living in Tower Hamlets and Hackney, London, UK.

The purpose of this study was to assess the prevalence of dental erosion in the maxillary incisors of a sample of 14-year-old schoolchildren and to explore the aetiological factors responsible for that erosion. The cross-sectionally design study took place in secondary schools in inner-city London, UK and involved 525, 14-year-old schoolchildren selected at random in a clinical examination and a self-completed questionnaire. The outcomes measures for dental erosion were; the prevalence, the area and depth of lesions and the risk factors. The prevalence of labial and palatal erosion was 16.9 per cent and 12 per cent respectively. Risk factors and behaviours including daily frequency of ingestion of acidic fruits and drinks, food vomiting, toothbrushing frequency, and swimming habits were not shown to have any relationship with the presence of erosion. It was concluded that the prevalence of erosion in the maxillary incisors of this sample was higher labially and lower palatally than in previously reported national figures. The risk factors which were investigated were not shown to have any relationship with the presence of erosion. Further investigations of these issues are necessary to establish whether or not dental erosion is a public health problem in the UK.

Dental service use and the implications for oral cancer screening in a sample of Bangladeshi adult medical care users living in Tower Hamlets, UK.

AIM: To assess the use of dental services, barriers to uptake of dental care and attitudes to regular dental examinations and the prevalence of tobacco and paan chewing habits in a group of Bangladeshi medical care users. DESIGN: Multi-centre cross-sectional study. SETTING: Four general medical practices' waiting areas in Tower Hamlets. SUBJECTS: Bangladeshi adults aged 40 years and over. INTERVENTION: An interview schedule. MAIN OUTCOME MEASURES: The prevalence of tobacco smoking and paan chewing with or without the addition of tobacco. The use of dental services, barriers to the use of dental services and attitudes to regular dental examinations. RESULTS: Results were obtained from 158 subjects (response rate 85%). 25% of the whole sample had never visited a dentist. These were significantly (P < 0.05) more likely to be women, who also thought regular check-ups were of little value. In their use of health services 73% experienced language difficulties. 33% of the sample were tobacco smokers. Paan was chewed by 78% of the sample with significantly (P < 0.05) more females than males adding tobacco to their quid and chewing more frequently than males. CONCLUSION: There are considerable barriers to be overcome if dental practices are to be the site for oral cancer screening and oral health promotion in this population. There are sex differences in reported behaviour and attitudes about use of dental services and in tobacco and paan use in this Bangladeshi sample. Further research is needed to establish why this ethnic minority attend general medical practices but not general dental practices.

On-line determination and control of fat content in batches of beef trimmings by NIR imaging spectroscopy.

An NIR imaging scanner was calibrated for on-line determination of the fat content of beef trimmings. A good calibration model was obtained for fat in intact beef (R=0.98, RMSECV=3.0%). The developed model could be used on single pixels to get an image of the fat distribution, or on the average spectrum from each trimming/portion of trimmings passing under the scanner. The fat model gave a rather high prediction error (RMSEP=8.7%) and a correlation of 0.84 when applied to 45 single trimmings with average fat content ranging from 1.6 to 49.3% fat. Test measurements on streams of trimmings making up batches varying from 10 to 24 kg gave a much lower prediction error (RMSEP=1.33%). Simulations based on true measurements indicate that the RMSEP decreases with increasing batch size and, for the present case, reached about 0.6% for 100 kg batches. The NIR scanner was tested on six batches of intact trimmings varying from 145 to 210 kg and gave similar fat estimates as an established microwave system obtained on the ground batches. The proven concept should be applicable to on-line estimation of fat in trimmings in order to determine the batch fat content and also to control the production of batches to different target fat levels. A possible requirement for the concept to work properly is that the trimming or layer of trimmings on the belt is not too thick. In this study maximum thickness was about 8 cm. Thicker trimmings might be measured, but careful hardware adjustments are then required.

Biosynthesis of nuclear proteins after stimulation of quiescent Swiss mouse 3T3 cells.

Stimulation of quiescent Swiss mouse 3T3 fibroblasts either by serum or by the low molecular weight hormones, prostaglandin F2 alpha and insulin, induces DNA synthesis after a lag period of about 15 h. Following restimulation by serum or these pure hormones there is an overall increase of two- to fourfold in the rate of biosynthesis of nuclear proteins. In addition, there is a relative decrease in some proteins (Mr = 200 X 10(3), pI 6.0-6.5), while others increase (e.g. actin). Two polypeptides show specific correlations with the exit from G0. The synthesis of p30 (Mr = 30 X 10(3), pI 5.2) is at a maximum within 5 h of restimulation, while the synthesis of p36 (Mr = 36 X 10(3), pI = 4.25) is first seen at 10-20 h after restimulation. Synthesis of p36 correlates well with the initiation of DNA synthesis. The synthesis of both proteins is stimulated by serum and by the hormones. Thus there are common biosynthetic responses to different stimuli indicating convergent pathways leading to DNA biosynthesis. Addition of hydrocortisone with the growth-stimulatory hormones inhibits both entry into the S phase and biosynthesis of p36. In contrast, hydrocortisone does not alter the biosynthesis of p30. This 'early' protein, p30, is different from the products of both c-fos and c-myc. Therefore, we have identified two specific components that might participate in the regulation of cell proliferation.

Variation in the length of the lag phase following serum restimulation of mouse 3T3 cells.

We have investigated the length of the lag phase (time taken for the first cells to enter S phase) and the kinetics of entry into DNA synthesis after serum restimulation of Swiss mouse 3T3 cell cultures that were allowed to become quiescent under different conditions. Cells were allowed to reach quiescence as a confluent monolayer in medium containing 10% (v/v) calf serum. Alternatively, when serum was reduced to 1% (v/v), cultures became quiescent at about 30% confluency and there was little cell to cell contact. The results show that the lag, or prereplicative phase becomes longer as the time spent in the quiescent state increases. This is the case in both confluent and non-confluent cultures. The rate of entry of cells into the S phase, however, remains the same under all conditions.

Differential control of tyrosine hydroxylase activation and catecholamine secretion by voltage-operated Ca2+ channels in bovine chromaffin cells.

Contributions of L-, N-, and P/Q-type voltage-operated Ca2+ channels to two responses of bovine adrenal chromaffin cells have been studied using the nonreceptor stimulus K+ depolarization. Tyrosine hydroxylase activity and catecholamine secretion were both increased by K+ over a similar concentration range and in a Ca(2+)-dependent manner. At a submaximal concentration of 20 mM K+, tyrosine hydroxylase activation was reduced by nitrendipine but unaffected individually by (+/-)-Bay K 8644, omega-conotoxin GVIA, omega-agatoxin IVA, and omega-conotoxin MVIIC. It was fully blocked by combined inhibition of L-, N-, and P/Q-type channels. With a maximal concentration of 50 mM K+, tyrosine hydroxylase activation was unaffected by nitrendipine as well as by each of the other drugs on its own; however, it was reduced by 71 % by combined inhibition of L-, N-, and P/Q-type channels. In contrast, catecholamine secretion with both 20 and 50 mM K+ was enhanced by (+/-)-Bay K 8644, partially inhibited by nitrendipine and omega-conotoxin MVIIC, and completely blocked by a combination of antagonists for L-, N-, and P/Q-type channels. The results show that Ca2+ entry through voltage-operated Ca2+ channels can differentially regulate distinct chromaffin cell responses and that this is an intrinsic property of the mechanisms by which Ca2+ entry activates these responses. It is not dependent on the parallel activation of other signaling events by receptors.

Poly(ADP-ribose) polymerase in plant nuclei.

We show that poly(ADP-ribose) polymerase is present in maize, pea and wheat nuclei. We have identified the enzyme product as poly(ADP-ribose) by purification and electrophoresis on a DNA sequencing gel. This reveals a polymer ladder consisting of up to 45 residues. The polymer product from maize, after digestion with snake venom phosphodiesterase, gave only 5'-AMP and (phosphoribosyl)-AMP; the mean chain length of the polymer was 5 and 11 residues in two separate experiments. The optimum pH of the plant enzyme is greater than pH 7.0 in pea, wheat and maize; the optimum temperature for enzyme activity is approximately 15 degrees C. The Km for NAD+ for the enzyme from maize is estimated to be approximately 50 microM under optimal conditions. Several compounds (nicotinamide, deoxythymidine, 3-aminobenzamide, 3-methoxybenzamide and 5-bromodeoxyuridine) that specifically inhibit the animal enzyme also inhibit the enzyme from plants. The ratio of the IC50 for 5-bromodeoxyuridine to the IC50 for 3-aminobenzamide in maize is similar to that of the animal enzyme indicating that the enzyme involved is poly(ADP-ribose) polymerase and not mono(ADP-ribosyl) transferase. SDS gel electrophoresis and gel filtration analysis of a crude extract of maize nuclei indicate a molecular mass for poly(ADP-ribose) polymerase of approximately 114 kDa.