Five-year follow-up of a cognitive-behavioural lifestyle multidisciplinary programme for childhood obesity outpatient treatment.

OBJECTIVE: Aim of this study is to examine the 5-year follow-up results of MI PIACE PIACERMI (I like to like and please myself), a cognitive-behavioural programme intended to obtain a weight growth regulation over an extended period. DESIGN: Longitudinal observational clinical study. SETTING: Hospital-based programme, through outpatient activities. SUBJECTS: Thirty-one simple obese children, 13 boys and 18 girls, 6-12 years of age on admission. INTERVENTION: The intervention was carried out by a multidisciplinary team (paediatrician, cognitive-behavioural psychologist, physical therapist). It employed cognitive-behavioural techniques, nutrition education, promotion of physical activity, setting a high value on free play in motion. The programme actively involves parents. The following measurements were taken on admission and at 5-year follow-up: height, weight, waist circumference, body mass index (BMI), BMI standardized (BMI-SDS), and adjusted BMI (a-BMI) as actual BMI/BMI (50th percentile)*100. Dietary habits were investigated by interview and 24-h recall. Parents completed the Family Habit Inventory and the Child Behaviour Checklist (CBCL). Motor skills were assessed by using Frostig's test. RESULTS: The dropout rate was 35.5%. In subjects who completed the 5-year follow-up, the mean and s.d. of BMI-SDS and a-BMI were, respectively, 4.23+/-0.71 and 54.7%+/-9.0 at baseline and 2.74+/-0.85 and 43.2%+/-17.3 at the last visit. Waist circumference decreased. Family habits improved significantly. Total energy intake was significantly reduced. Emotional and social aspects of obesity-related behaviours showed positive changes. Motor skills globally improved. CONCLUSIONS: The study provides further evidence that positive persistent results may be obtained in obese children with treatment programmes combining a lifestyle centred approach, parental involvement, nutrition education and cognitive-behavioural strategies.

Bone quality assessed by phalangeal quantitative ultrasonography in children and adolescents with isolated idiopathic growth hormone deficiency.

OBJECTIVE: Some observations indicate that GH deficiency (GHD) may have little impact on bone mineralization in contrast to its effects on bone growth and maturation. The aim of the present study was to evaluate the effects of isolated GHD and GH-replacement therapy on bone quality assessed by a quantitative ultrasound (QUS) technique at the proximal phalanges of the hand. DESIGN: Growth and QUS data of 68 subjects (50 males and 18 females) aged 5-18 yr with isolated GHD were retrospectively examined. A cross-sectional series of 120 observations was collected and compared with data obtained from a control population (1227 healthy children, 641 males and 586 females, aged 3-16 yr). METHODS: QUS variables amplitude- dependent speed of sound (AD-SoS) and bone transmission time (BTT) were assessed by the sonographic device DBM Sonic BP IGEA. Height and weight measurements were performed according to standard techniques. In patients, skeletal age (SA) was determined by Tanner-Whitehouse method (3rd version). RESULTS: Before treatment height, SA, ADSoS and BTT were reduced in patients. Height SD score (SDS), SA SDS, AD-SoS SDS, and BTT SDS improved during treatment. Significant associations of both AD-SoS and BTT with age, SA, height, and therapy duration were observed. Using multivariate regression models the disease state, SA, and height proved to be significant variables in predicting BTT and AD-SoS. CONCLUSIONS: QUS measurements adjusted for body size and skeletal maturity in GHD patients seem to be only slightly reduced. A body size and skeletal maturity adjustment should be incorporated in studies on bone mass in GHD children and adolescents. A non-invasive technique such as QUS technology opens new perspectives.

Longitudinal assessment of bone quality by quantitative ultrasonography in children and adolescents.

Among the techniques available to assess bone quality, quantitative ultrasonography of the proximal phalanges of the hand (QUS) has emerged as particularly attractive. In this study, amplitude-dependent speed of sound (AD-SoS) and bone transmission time (BTT) were obtained by the sonographic device DBM Sonic BP IGEA in two sessions at two years' interval, in a school-age population (589 subjects, 290 mol/L and 299F, aged 3 to 16 y) with the aim to determine accuracy of QUS measurements, evaluate QUS variable changes during growth, relate these values with age and growth variables. Mean AD-SoS and BTT at age classes from 5 to 12 y as determined at the first and second measurement sessions were not significantly different. A significant increment (p < 0.0001) between the first and the second measurement was observed for both QUS variables. AD-SoS and BTT showed significantly different variations in the various age groups (ANOVA). Correlations were found of AD-SoS and BTT increments with age, height, weight, pubertal stage and with height growth velocity (p < 0.05). AD-SoS and BTT increment curves presented a very similar trend decreasing from 4 to 7 y of age. Thereafter a plateau was reached up to the age of 10 to 11 y in girls and 11 to 12 y in boys, when an increase was observed corresponding to pubertal growth rate acceleration. In conclusion, the present study would confirm that QUS measurements are accurate. Ad-SoS and BTT increment models are similar to most growth velocity curves and follow a strongly age- and growth-dependent pattern.

Structural synaptic remodeling in the perirhinal cortex of adult and old rats following object-recognition visual training.

The ultrastructural features of layer II synapses in the perirhinal cortex of adult (4- to 6-month-old) and old (25- to 27-month-old) rats exposed to a six-session object recognition visual training were investigated by morphometric methods. The comparative analysis showed a higher synaptic numeric density, a lower synaptic average area, and a lower percentage of megasynapses (S > 0.5 microm2) in old trained rats versus controls, and a higher percentage of small (S < 0.15 microm2) junctions in adult trained rats versus controls. The more marked synaptic remodeling underlying memory consolidation in the perirhinal cortex of old rats might reflect a pre-existing lower dynamic status.

The ethanol self-administration context as a reinstatement cue: acute effects of naltrexone.

A major difficulty in treating alcohol addiction is the high rate of relapse even after prolonged abstinence. Relapse can be triggered by several factors, including stress, re-exposure to the drug, conditioned discrete stimuli and exposure to the context in which alcohol consumption occurred. The present study investigated the role played by the environmental context on ethanol relapse using an extinction/reinstatement animal model: rats were trained to self-administer ethanol in a distinctive context, and extinction occurred in a setting that differed by visual, tactile and olfactory properties; reinstatement was tested by placing the animals into the ethanol-associated context in the absence of ethanol. We found that re-exposure to the ethanol-associated context significantly increased responses on the ethanol-paired lever. The increase in responding required the presence of the complete configuration of the multimodal context. The non-selective opioid receptor antagonist naltrexone (0.3 mg/kg) administered 20 min prior to the reinstatement test significantly attenuated context-induced reinstatement of lever press responding, compared with saline-treated subjects. These data indicate that the environmental context associated with ethanol availability influences ethanol-seeking behavior in the rat, and that endogenous opioids are involved in this process. Our findings are in accordance with clinical reports demonstrating naltrexone efficacy in the treatment of alcohol relapse in humans, and indicate that the context-induced reinstatement model described here may be useful to investigate the biological mechanisms underlying alcohol relapse.

Fetal spine ossification: the gender and individual differences illustrated by ultrasonography.

The spatial and temporal pattern of manifestation of ossification nuclei of the spinal column in fetal life have been well established by histologic and radiologic studies. Sonographic evaluation of the fetal spine depends on visualization of the ossification centers, but the sequence of development of ossification centers in the vertebral column obtained by embryologists and sonographers and radiology are conflicting. We carried out a longitudinal study to establish the ultrasonographic appearance and timing of development of primary ossification centers of the fetal spine in the first and second trimesters of pregnancy. A total of 80 mothers were evaluated during their pregnancy with two echographic controls; in the first trimester, the spine length was measured and, in the second trimester of pregnancy, the timing of ossification of the bodies and neural arches of sacral vertebrae and the difference in appearance between the female and male genders were evaluated. Spinal length measurements obtained in the first trimester and percentage of detection of sacral vertebral structures increased progressively with a regular pattern in relation to gestational age. Spinal length at first ultrasound examination was slightly correlated with time of appearance of sacral bodies and arches. Ossification timing was significantly earlier in females than in males. The study has attempted to improve our understanding of the sonographic detection of the spinal ossification. Data presented give some further information on the stages of appearance of sacral vertebrae body centers during intrauterine development. Differences between genders and interindividual variations in ossification timing were observed at a very early stage of development. This could be of value when fetal growth is evaluated. Moreover, further knowledge of spinal development may be useful for early diagnosis of spinal abnormalities and for fetal biometrics.

Bone quality in perinatally HIV-infected children: role of age, sex, growth, HIV infection, and antiretroviral therapy.

Appropriate supportive care and identification of long-term sequels of therapy are of paramount importance in HIV-infected pediatric patients. As low bone mineral quality (BMQ) in patients can be considered a marker of possible degeneration in osteopenia and osteoporosis in adulthood, we evaluated bone features in a pediatric population. Forty-four patients (23 females, 21 males; aged 3-17 years) were compared with a control population (1227 healthy children: 568 females, 641 males; aged 3-18 years). Seven patients were CDC stage C, 18 B, and 18 A. All patients were vertically infected; four were naive to any antiretroviral treatment, seven were taking two NRTIs, and 32 were on HAART. BMQ was assessed by a quantitative ultrasound (QUS) technique. It measures the amplitude-dependent speed of sound (AD-SoS, m/sec) and the bone transmission time (BTT, microsec). QUS values were significantly lower in cases than in controls, even after adjustment for age and body size (AD-SoS: 1924.7 +/- 64.9 and BTT: 0.97 +/- 0.3 in controls; AD-SoS: 1879.7 +/- 57.2 and BTT: 0.80 +/- 0.32 in cases; p < or = 0.001). The associations of AD-SoS and BTT with gender, type of therapy, and CDC stages were not significant. AD-SoS and BTT were significantly associated with age (r = 0.59, p < 0.0001), skeletal age SDS (r = 0.46, p = 0.002), height (r = 0.66, p < 0.0001), and therapy duration (r = 0.31, p = 0.04). Both AD-SoS and BTT values in patients fell below mean values of controls. Follow-up of bone mineral density is important in patients to prevent long-term problems of skeletal status.

Ossification timing of sacral vertebrae by ultrasound in the mid-second trimester of pregnancy.

OBJECTIVES: The aim of the study was to establish the ossification timing of sacral vertebrae by ultrasonography in the second trimester of pregnancy, for the diagnosis of caudal regression syndrome with isolated sacral agenesis. METHODS: The study was carried out on 77 normal single pregnancies, at gestational ages ranging from 15 to 21 weeks, using high-resolution transabdominal echography. The sacral region was visualized in a coronal plane, when the fetus was in anterodorsal position. The level of ossification of sacral vertebrae (S1 to S5) at each gestational age was recorded. Each sacral region was examined three times by the same observer and the nucleus was considered as present when it was visualized at least two times out of three. Blind assessment was performed three times by a second observer, who was not present at the previous examination, for interobserver and intraobserver error analysis. RESULTS: Interobserver and intraobserver error calculation demonstrated the reproducibility of the method. Concordance between the two observers as evaluated by Cohen Kappa index was 0.77 (C.I. 95%, 0.69-0.85).S1 ossification nuclei were visualized in all fetuses at 15 weeks and S2 nucleus was found in all fetuses within 17 weeks. S3 nucleus was detected in 45% of fetuses by the beginning of the 16th week. S4 was visualized in 55% of the cases at 18 weeks and progressively in a higher percentage of cases during the following weeks of gestation. CONCLUSION: The data obtained showed that the sequence of development of sacral region ossification was related to gestational age. This observation allows clinicians to accurately exclude isolated sacral agenesis at 16 to 17 weeks of gestation, when the S1-S2 ossification nuclei are visualized. This opportunity may be of particular value in the offspring of diabetic mothers.

Influence of age, sex, and growth variables on phalangeal quantitative ultrasound measures: a study in healthy children and adolescents.

Skeletal status by phalangeal quantitative osteosonography (DBM Sonic BP-IGEA) was examined in 1227 healthy children (641 boys and 586 girls) aged 3-16 years. Aims of the study were to evaluate some physical parameters pertaining to the ultrasound transmission crossing the phalanx in a school-age population and to relate these values to age, sex, and growth variables. A correlation was found between AD-SoS (amplitude-dependent speed of sound) and BTT (bone transmission time) and, age, height, weight, and pubertal stage, respectively. No correlation existed between FWA (fast wave amplitude) and SDy (dynamics of the ultrasound signal) and age, height, weight, pubertal stage, and BMI, respectively. AD-SoS increased in boys until 7-8 years of age. Thereafter a plateau was reached up to age 12-13 years, when a rapid increase was observed corresponding to pubertal growth rate acceleration. In girls, AD-SoS increased with age up to 10-11 years with a steeper increase at the time of puberty starting about 2 years earlier than in boys. BTT presented a similar trend. Mean AD-SoS values increased from Tanner pubertal stages 1 to 2 and from stage 3 to 4 in both sexes. Significantly higher mean AD-SoS values in stages 2, 3, and 4 were observed in girls as compared to boys. Mean BTT values increased significantly from stage 1 to 5 in girls and from 1 to 4 in boys. QUS technology showed the ability to assess bone changes in the growing bone.

Spine length measurement in the first trimester of pregnancy.

OBJECTIVES: The aim of the study was to evaluate spine length as an indicator of skeletal growth in the first trimester of pregnancy and to provide a nomogram of spine length at the end of the first trimester of pregnancy. METHODS: The study was carried out on 420 single pregnancies, at gestational ages ranging from 11 to 14 weeks, using high-resolution transabdominal echography. Biparietal diameter and crown-rump length (CRL) were measured to date the pregnancy. Using the same scanning plane used to measure CRL, the whole spine length in antero-dorsal position can be visualized as a double hyperechoic line from 10 weeks of gestation onwards. Spine length was measured three times by one observer and the mean of the three measurements was considered as definitive. Forty fetuses had multiple measurements for interobserver and intraobserver error analysis. RESULTS: Linear relationship between spine length, and gestational age, biparietal diameter and CRL were demonstrated. Spine length (millimetres) as a function of gestational age (days) was expressed by the regression equation: spine length = 1.09 x (gestational age in days) -60.56, with a determination coefficient of R(2) = 0.744. Spine length ranged from 21.5 mm at 11 weeks to 41.9 mm at 14 weeks. CONCLUSION: The data obtained showed that spine length increased progressively from the end of the first trimester to the beginning of the second. A high correlation between spine length, gestational age, biparietal diameter, and CRL was observed. Spine length measurement could therefore be considered a good indicator of fetal growth.

Prefrontal cortex lesions augment the location-related firing properties of area TE/perirhinal cortex neurons in a working memory task.

It has previously been proposed that prefrontal cortex may have some role in keeping temporal cortex-based representations "on-line" during a working memory task. To test this hypothesis, the effects of electrolytic prefrontal cortex lesions on the firing of area TE and perirhinal cortex (PRC) neurons were examined while rats performed a delayed non-match to position task in the T-maze. The behavioural performance of control (n = 4) and lesioned (n = 4) animals were similar during this task, and many neurons displayed a statistically significant location-related variation in firing rate during the sample (44/56 neurons) and test (39/56 neurons) phases. Units from prefrontal-lesioned animals (82%) were more likely to display a significant variation in firing across the maze compared to controls (50%; P < 0.01), and to have more discrete location-related properties (50% of neurons) compared to the control (5%) group (P < 0.0005). This finding suggests that prefrontal cortex normally modulates the transmission and/or processing of spatial information in area TE/PRC during a working memory task. Modulation could be mediated through direct connections between the structures or via prefrontal control of subcortical structures. This finding has implications for our understanding of prefrontal-temporal involvement in memory and cognitive disorders.

Longitudinal distance standards of fetal growth. Intrauterine and Infant Longitudinal Growth Study: IILGS.

BACKGROUND: Most ultrasonographic fetal growth norms are derived from cross-sectional data or from longitudinal data treated as coming from cross-sectional studies, although only longitudinal models may detect particular aspects of fetal growth shape, such as peak of growth velocity. MATERIALS AND METHODS: The sample included 238 singleton normal pregnancies. All the fetal traits under study (biparietal diameter, occipito-frontal diameter, head circumference, femur diaphysis length and abdomen circumference) were measured according to the classical ultrasound techniques by highly trained operators. Individual growth profiles (made up of 5 to 9 measures) were taken at regular intervals between the 12th and the 40th week. Growth norms were traced by means of a two-stage linear model: (I) a 3-constant fetal growth function was fitted to each individual growth profile, (II) growth centiles were based upon the weighted mean and covariance matrix of the individual growth constants. RESULTS: Fetal growth curves show a sigmoid shape with a maximum slope (i.e. a peak growth velocity) which occurs earlier for head diameters (about 18 weeks), later for femur diaphysis length (20 weeks) and abdomen circumference (22 weeks). During intrauterine growth, all traits show a progressive increase in interindividual variability, which is more prominent for abdomen circumference. CONCLUSION: The mathematical model applied to a large sample of growth profiles provided a satisfactory description of the individual fetal development and its biological variability, and allowed the construction of longitudinal distance standards useful for clinical purposes.

Use of the new US90 standards for TW-RUS skeletal maturity scores in youths from the Italian population.

Recently, 1997, Tanner and co-workers provided a new scale converting TW-RUS standard maturity scores to skeletal age for European North American youths (US90). The aim of the present study was to test if the accuracy of TW-RUS bone age assessments in the Italian population could be improved by evaluating the estimates obtained with this new scale in comparison with other standards (UK60: original British series, B70: Belgian series and S80: Spanish series). 1,831 hand-wrist radiographs (Italian healthy subjects aged from 8 to 16.8 years) were evaluated. The US90 reference values are resulted the most suitable TW-RUS standards. Therefore, it seems useful to update the reference values of TW-RUS SMS in Italian youths, using this new scale.

Selective cardiodepressant activity of fluodipine, a fluorenone-1,4-dihydropyridine derivative.

The effect of the dihydropyridine derivative, 1,4-dihydro-2,6-dimethyl-4-(fluorenon-4-yl)pyridine-3,5-dicarboxyl ic acid diallyl ester (fluodipine) was studied in vitro in different rabbit, rat and guinea pig preparations and in vivo in the rabbit in order to characterize its pharmacological profile at cardiac and at vascular sites. Compared to nifedipine, fluodipine showed a similar cardiodepressant activity, and a much lower inhibitory activity on vascular contraction. The highest tissue selectivity was observed in guinea pig preparations: fluodipine was about 2-3 times more effective than nifedipine on chronotropism and inotropism in isolated atria, and about 150 times less effective on aortic strip contraction. Accordingly, fluodipine (i) showed high-affinity binding to guinea pig ventricular L-type cardiac Ca2+ channels (Ki=2.57 nM), (ii) was about 80 times less effective than nifedipine to inhibit Ca2+ influx in vascular smooth muscle cells and (iii) induced a significant reduction of heart rate in the anesthetized rabbit (ID25=8.5 mg kg(-1), i.v.) without affecting the blood pressure up to 20 mg kg(-1), whereas nifedipine showed a significant hypotensive effect at very low doses (ID25=0.18 mg kg(-1), i.v.). The pacemaker current If of rabbit sino-atrial node myocytes was not affected by fluodipine. These findings demonstrate that fluodipine exerts selective cardiodepressant activity, likely due to a higher affinity for cardiac than for vascular Ca2+ channels.

Trichorhinophalangeal syndrome type I in monozygotic twins discordant for hip pathology. Report on the morphological evolution of cone-shaped epiphyses and the unusual pattern of skeletal maturation.

A pair of monozygotic twin girls with trichorhinophalangeal syndrome type I (TRPS I), followed from 8.3 to 16.1 years of age, is described. Both showed typical dysmorphic features and severe short stature, but only one had Perthes-like changes in the right capital femoral epiphysis. The radiographic findings and evolutionary changes of phalangeal cone-shaped epiphyses (PCSE) of the hands are illustrated in this report. The unusual bone maturation and growth of the twins are also described. Both presented poor growth and delayed bone age until about 13 years, followed by marked acceleration of bone age and stunted pubertal height spurt.

Rescue of implantation potential in embryos with poor prognosis by assisted zona hatching.

The effect of the assisted zona hatching (AZH) procedure was investigated on 135 cycles with a poor prognosis of pregnancy due to: (i) maternal age > or = 38 years (45 cycles); (ii) three or more failed in-vitro fertilization (IVF) attempts (70 cycles), and (iii) patients possessing both inclusion criteria (20 cycles). The control groups (113 cycles) included patients possessing the same characteristics (42, 53 and 18 cycles respectively) and who did not undergo the AZH procedure. A total of 505 embryos was treated with AZH before transfer, resulting in: 14, 25 and 6 clinical pregnancies. The percentage of clinical pregnancies per cycle was significantly higher than controls for the first (31 vs 10% in control 1, P < 0.05) and second groups (36 vs 17% in control 2, P < 0.05). No significant difference in percentage of clinical pregnancies was found for the third group (30 vs 6%). Similarly, higher rates of implantation were obtained (11.5, 15 and 11%) compared to the respective controls (4%, P < 0.02; 6.3%, P < 0.01; and 1.5%). The rate of miscarriage in the AZH groups was similar to that obtained in the controls (22 vs 21%). Finally, the morphological analysis of the embryos transferred revealed that the poor prognosis condition is associated to a significantly slower rate of development and a higher rate of fragmentation. The present results indicate that AZH procedure improves pregnancy and implantation rates in patients with a poor prognosis of pregnancy by facilitating the hatching process in embryos which would otherwise be trapped inside the zona pellucida.

Long-term follow-up of skeletal dysplasia in thalassaemia major.

We report skeletal changes due to deferoxamine (DF) in 15/29 patients with transfusion-dependent thalassaemia major (TM), followed longitudinally for growth assessment. Clinically the earliest signs were decline in height and/or sitting height growth rate, leg and back pain with restricted movement and limb deformity. Radiologically metaphyseal and spinal changes were seen in 5 subjects and vertebral lesions alone in 10. The metaphyseal changes were mild, moderate or severe and affected all long bones, but were most pronounced at wrists and knees. They progressed from widening of the growth plate and defects of metaphyseal margins to appearance of radiolucent pseudocystic areas and, in severe cases, of cupped, rickets-like metaphyses. The spinal changes proceeded from osseous defects of ventral upper and lower edges of vertebrae and biconvex contours of end-plates to platyspondyly with decreased vertebral body height. After DF dose reduction, metaphyseal changes regressed in 2 patients, while they progressed in 3, requiring corrective surgery for severe valgus knee. Spinal abnormalities either remained unchanged or progressed. Final height was very short in patients with spondylometaphyseal lesions, short and disproportionate in patients with only spinal involvement.

Chemiluminescence imaging in bioanalysis.

The development, analytical performance and applications of chemiluminescence imaging as a tool for quantitative analyte localization in target biological specimens are described. The detection of acetylcholinesterase activity both in array format and on a target surface are described. A proposed application of the method is a 384 well microtiter format assay for high throughput screening of acetylcholinesterase inhibitors such as tacrine, a drug widely used in the treatment of Alzheimer's disease, and two recently developed analogues. The chemiluminescent system in conjunction with optical microscopy allowed localization of acetylcholinesterase in brain tissue sections. We also describe the chemiluminescent immunohistochemical localization of interleukin 8 in Helicobacter pylori infected gastric mucosa cryosections and an in situ hybridization assay for the detection of herpes simplex virus DNA in single cells.

Ca2+ and Na+ permeability of high-threshold Ca2+ channels and their voltage-dependent block by Mg2+ ions in chick sensory neurones.

1. The Mg2+ block of Na+ and Ca2+ currents through high-voltage activated (HVA; L- and N-type) Ca2+ channels was studied in chick dorsal root ganglion neurones. 2. In low extracellular [Ca2+] (< 10(-8) M) and with Na+o and Cs+i as the main charge carriers (120 mM), HVA Na+ currents started to activate at -40 mV, reached inward peak values near 0 mV and reversed at about +40 mV. 3. Addition of 30-500 microM Mg2+ to the bath caused a strong depression of inward Na+ currents that was voltage and dose dependent (KD = 39 microM in 120 mM Na+ at -10 mV). The block was maximal at negative potentials (< -70 mV) and decreased with increasing positive potentials, suggesting that Mg2+ cannot escape to the cell interior. 4. Block of Ca2+ currents by Mg2+ was also voltage dependent, but by three orders of magnitude less potent than with Na+ currents (KD = 24 mM in 2 mM Ca2+ at -30 mV). The high concentration of Mg2+ caused a prominent voltage shift of channel gating kinetics induced by surface charge screening effects. To compensate for this, Mg2+ block of inward Ca2+ currents was estimated from the instantaneous I-V relationships on return from very positive potentials (+100 mV). 5. Inward Na+ and Ca2+ tail currents following depolarization to +90 mV were markedly depressed, suggesting that channels cleared of Mg2+ ions during strong depolarization are quickly re-blocked on return to negative potentials. The kinetics of re-block by Mg2+ was too fast (< 100 microseconds) to be resolved by our recording apparatus. This implies a rate of entry for Mg2+ > 1.45 x 10(8) M-1 S-1 when Na+ is the permeating ion and a rate approximately 3 orders of magnitude smaller for Ca2+. 6. Mg2+ unblock of HVA Na+ currents at +100 mV was independent of the size of outward currents, whether Na+, Cs+ or NMG+ were the main internal cations. 7. Consistent with the idea of a high-affinity binding site for Ca2+ inside the channel, micromolar amounts of Ca2+ caused a strong depression of Na+ currents between -40 and 0 mV, which was effectively relieved with more positive as well as with negative potentials (KD = 0.7 microM in 120 mM Na+ at -20 mV). In this case, the kinetics of re-block could be resolved and gave rates of entry and exit for Ca2+ of 1.4 x 10(8) M-1 S-1 and 2.95 x 10(2) s-1, respectively. 8. The strong voltage dependence and weak current dependence of HVA channel block by divalent cations and the markedly different KD values of Na+ and Ca2+ current block by Mg2+ can be well described by a previously proposed model for Ca2+ channel permeation based on interactions between the permeating ion and the negative charges forming the high-affinity binding site for Ca2+ inside the pore (Lux, Carbone & Zucker, 1990).