Characteristics of visual feedback in postural control during standing

In the present study, the visual feedback system in postural control was investigated. To suppress the vestibular and proprioceptive feedback paths, a subject stood on a force-measuring plate with a fixed back support. Because the subject's body was immovable under these conditions, the subject controlled a computer model which simulated body dynamics. Information on the sway angle of the model was fed visually. Under this condition, frequency response functions for the ankle moment in response to the sway angle were calculated. The experimental results suggest that the visual feedback system contains a large time delay and, consequently, the visual system does not by itself allow a subject to maintain an upright posture. Index Terms- Feedback control, frequency characteristics, identification, posture, visual sensory feedback.

Identification of ligand effector binding sites in transmembrane regions of the human G protein-coupled C3a receptor

The human C3a anaphylatoxin receptor (C3aR) is a G protein-coupled receptor (GPCR) composed of seven transmembrane alpha-helices connected by hydrophilic loops. Previous studies of chimeric C3aR/C5aR and loop deletions in C3aR demonstrated that the large extracellular loop2 plays an important role in noneffector ligand binding; however, the effector binding site for C3a has not been identified. In this study, selected charged residues in the transmembrane regions of C3aR were replaced by Ala using site-directed mutagenesis, and mutant receptors were stably expressed in the RBL-2H3 cell line. Ligand binding studies demonstrated that R161A (helix IV), R340A (helix V), and D417A (helix VII) showed no binding activity, although full expression of these receptors was established by flow cytometric analysis. C3a induced very weak intracellular calcium flux in cells expressing these three mutant receptors. H81A (helix II) and K96A (helix III) showed decreased ligand binding activity. The calcium flux induced by C3a in H81A and K96A cells was also consistently reduced. These findings suggest that the charged transmembrane residues Arg161, Arg340, and Asp417 in C3aR are essential for ligand effector binding and/or signal coupling, and that residues His81 and Lys96 may contribute less directly to the overall free energy of ligand binding. These transmembrane residues in C3aR identify specific molecular contacts for ligand interactions that account for C3a-induced receptor activation.

Ligand binding sites on guinea pig C3aR: point and deletion mutations in the large extracellular loop and vicinity

Human C3a receptor (huC3aR) belongs to the G-protein coupled receptor family chacterized by having seven transmembrane domains. The huC3aR is a unique member of this family having a large extracellular (EC) loop of 175 amino acids between the 4th and 5th transmembrane domains. Based on a comparison of C3aR sequences from several species, a number of charged and conserved amino acids (Asp182, Asp309, Asp310, and Arg331) in and near the large EC loop of guinea pig C3aR were replaced using site-directed mutagenesis. Competitive binding assays showed that changing Arg331 in guinea pig C3aR to Ala (or Gln), but not changing Asp182, Asp309, or Asp310 to Ala, resulted in complete loss of ligand binding activity. These results and major EC loop deletions demonstrated that an essential C3a binding site is present in the transmembrane portion of C3aR, but not in the large EC loop. Replacement of Arg331 by a noncharged residue was sufficient to eliminate ligand-receptor interactions.

Cloning and preliminary pharmacological characterization of the anaphylatoxin C5a receptor in the rabbit

1 The rabbit receptor for C5a was cloned from a genomic library and found to be 79.5% identical to the human homologue, the highest degree of similarity found so far in nonprimate laboratory animals. 2 The rabbit C5a receptor stably expressed in RBL cells binds human 125I-C5a (2 nM). Unlabelled C5a and the C-terminal analogue N-acetyl-Tyr-Ser-Phe-Lys-Pro-Met-Pro-Leu-D-Ala-Arg (Ac-YSFKPMPLaR) were found to be competitors of that binding, the peptide analogue retaining approximately 0.1% of the affinity of human C5a. 3 The order of potency human C5a>Ac-YSFKPMPLaR was conserved in bioassays based on rabbits (relaxation of the isolated portal vein and pulmonary artery; acute in vivo neutropenia), but with a decreasing potency gap between the two compounds, a likely consequence of the resistance to peptidases of the analogue. 4 The molecular definition of the rabbit C5a receptor evidenced a high preservation degree of sequence and pharmacologic properties relative to the human ortholog receptor, thus defining a set of molecular tools for the investigation of the role of C5a in physiologic and pathologic models based on the rabbit (e.g. atherosclerosis, inflammation).

Alteration in amino acids in motor neurons of the spinal cord in amyotrophic lateral sclerosis

Little is known concerning the changes of amino acid composition in different regions of the spinal cord in patients with amyotrophic lateral sclerosis (ALS). We performed quantitative amino acid analyses in the posterior funiculus, the lateral corticospinal tract, and the anterior horn of cervical enlargement of the spinal cord from seven ALS patients, and the results were compared with those of seven patients with other neurologic diseases (control A) and seven patients without neurologic diseases (control B). The levels of collagen-associated amino acids, hydroxyproline, proline, glycine, and hydroxylysine, were markedly lower in the lateral corticospinal tract and the anterior horn of ALS patients than in controls A and B. The contents of the acidic amino acids glutamate and aspartate were also significantly decreased in the lateral corticospinal tract and the anterior horn of ALS patients as compared with those of controls A and B. These data suggest that decreased contents of collagen-associated amino acids and excitatory amino acids are related to the degeneration of the upper and lower motor neurons in the spinal cord in ALS.

A simple radiographic measurement method for polyethylene wear in total knee arthroplasty

This study describes a new method for evaluating polyethylene wear in total knee arthroplasty. Since the amount of wear is dependent on a number of variables such as the weight and activity of the patient, it should be estimated based on in vivo measurements. We used a computer vision technique called three-dimensional/two-dimensional (3-D/2-D) matching to perform in vivo assessment using a single-plane radiograph. Using the 3-D/2-D matching algorithm we estimated the 3-D position and orientation of each knee implant and then measured the femorotibial distance, which is defined as the shortest perpendicular distance from the tibial tray to the femoral component. The accuracy of the proposed 3-D/2-D matching method was determined by in vitro investigations. The worst errors in in-plane/out-of-plane translations and rotations were 0.20/1.95 mm and 0.17/0.29 degrees, respectively. The root-mean-square error in femorotibial distance measurements using real polyethylene inserts was 0.04 mm. Results of in vivo femorotibial distance measurements are also described.

[Hyperkalemia after irradiated blood transfusion]

A 70-yr-old woman was scheduled for hepatectomy and colectomy. We gave general anesthesia with N2O-O2-Isoflurane and continuous epidural block. About 4.5 hours after the start of the operation, 8 units of irradiated RBC-MAP were transfused. Then elevated T waves were noted and serum potassium was increased to 5.4 mmol.l-1. The transfusion of RBC-MAP was stopped and calcium gluconate was administered immediately. Then serum potassium decreased to 4.3 mmol.l-1 and ECG returned to normal. During the operation, 10 units of irradiated RBC-MAP were transfused and 8 units of them had been stored more than 1 week after the irradiation. We suspect that hyperkalemia was induced by high concentration of potassium in RBC-MAP. Irradiation of blood products is an effective way to prevent post-transfusion graft versus host disease. However, the increase in potassium is greater in the irradiated than nonirradiated RBC-MAP. We must pay attention to the high concentration of potassium in th eplasma of RBC-MAP stored after irradiation.

[Unruptured aneurysm of the right sinus of Valsalva: a case report]

A previously healthy and asymptomatic 45-year-old woman was referred for evaluation of a heart murmur and an unusual dilatation in the aortic root. Transthoracic and transesophageal echocardiography, computed tomography, magnetic resonance imaging, and cardiac catheterization revealed an aneurysm with a maximum diameter of 6.0 cm in the right sinus of Valsalva. Aortic regurgitation and stenosis at the right ventricle outflow tract were associated with the aneurysm. Surgery and histological study demonstrated that the sinus of Valsalva aneurysm was enormously dilated with idiopathic degenerative change in the aortic media. The aneurysm was tremendously large compared to any previously reported. Decrease in pressure load during diastole caused by aortic regurgitation probably resulted in the growth of this huge aneurysm without rupture.

Loss of catecholaminergic neurons in the medullary reticular formation in myotonic dystrophy

OBJECTIVE

To clarify the possible relation between the extent of involvement of catecholaminergic neurons and the presence of alveolar hypoventilation in patients with myotonic dystrophy (MyD).

BACKGROUND

Respiratory insufficiency has been reported frequently in MyD patients. Recent data support the hypothesis that this respiratory failure results from a primary dysfunction of the CNS.

METHODS

The authors performed a quantitative immunoreactive study of tyrosine hydroxylase immunoreactive (TH+) neurons linked to hypoventilation in the dorsal central medullary nucleus (DCMN), the ventral central medullary nucleus (VCMN), and the subtrigeminal medullary nucleus (SMN)--where the autonomic respiratory center is thought to be located--in eight MyD patients and in 10 age-matched control subjects. Alveolar hypoventilation of the central type was present in three of the MyD patients but not in the remaining MyD patients or the control subjects.

RESULTS

The densities of TH+ neurons of the DCMN, the VCMN, and the SMN in MyD patients with hypoventilation were significantly lower than in those without hypoventilation (p < 0.02, p < 0.01, and p < 0.01, respectively) and control subjects (p < 0.01, p < 0.01, and p < 0.01, respectively).

CONCLUSIONS

These data suggest that the loss of TH+ neurons of the DCMN, the VCMN, and the SMN is associated with the presence of hypoventilation in MyD and may be an important feature of MyD.

Molecular cloning of two isoforms of the guinea pig C3a anaphylatoxin receptor: alternative splicing in the large extracellular loop

The anaphylatoxin C3a is released from C3 during complement activation. C3a is a potent spasmogen and has recently been described as an eosinophil and mast cell chemotactic factor that mediates a number of inflammatory reactions. Previously, we demonstrated the presence of a specific C3a receptor (C3aR) on guinea pig platelets. We report here the isolation of cDNA clones encoding for two isoforms of guinea pig C3aR (gpC3aR). Hydropathy analysis of the deduced amino acid sequence of both gpC3aR clones indicated seven transmembrane domains with a large extracellular (EC) loop between the fourth and fifth transmembrane domains, which is a known characteristic of the human C3aR. Northern blot analysis revealed that the gpC3aR was abundantly expressed on macrophages and in the spleen. A comparison of the deduced amino acid sequence of the larger gpC3aR (gpC3aR-L) with the recently cloned human C3aR indicated a 59.5% identity. The deduced amino acid sequence of the second, smaller cDNA clone was identical with gpC3aR-L, except that it lacked 35 amino acids in the large EC loop. Our evidence indicates that alternative splicing occurred in the large EC loop that accounts for these two isoforms. L cells separately expressing one of these two isoforms of the gpC3aR showed similar high-affinity C3a binding. An RT-PCR analysis documented that both forms of the C3aR were expressed in a variety of guinea pig tissues. The cloning and expression of these two natural forms of gpC3aR cDNA indicated that the deletion of the 35-residue portion of the large EC loop of gpC3aR-L did not alter C3a binding.

A modified back-propagation method to avoid false local minima

The back-propagation method encounters two problems in practice, i.e., slow learning progress and convergence to a false local minimum. The present study addresses the latter problem and proposes a modified back-propagation method. The basic idea of the method is to keep the sigmoid derivative relatively large while some of the error signals are large. For this purpose, each connecting weight in a network is multiplied by a factor in the range of (0,1], at a constant interval during a learning process. Results of numerical experiments substantiate the validity of the method.

Cloning and characterization of the guinea pig C5a anaphylatoxin receptor: interspecies diversity among the C5a receptors

The anaphylatoxin C5a receptor (C5aR, CD88 in man) plays a prominent role in mediating inflammatory and host defense processes. Direct evidence of C5aR involvement in host defense mechanisms was demonstrated recently using C5aR knockout mice. Mice deficient in C5aR were unable to clear intrapulmonary-instilled bacteria. The guinea pig system is perhaps unique for exhibiting cross-reactivity with human complement components and its high sensitivity to anaphylatoxins. Therefore, we cloned the guinea pig C5aR from a megakaryocyte cDNA library. The deduced amino acid sequence of guinea pig C5aR is 67% identical to human, 61.6% to dog, 60.2% to mouse and 63.6% to rat C5aR. Transient expression of guinea pig C5aR in COS-7 cells and stable expression on L cell fibroblasts were confirmed by FACS analysis. Competitive binding studies using [125I]C5a and stimulation of calcium mobilization by C5a proved that functional C5aR was expressed on these stably transfected L cells. The N-terminal extracellular region of guinea pig C5aR was five to seven residues shorter than the same region in C5aR from other species and sequence homology was limited to 11%. Other outer membrane loops were also poorly conserved (8-33%) when compared across five species. Transmembrane segments were highly conserved between these various species (46-86%). Guinea pig C5aR binds human C5a, therefore residues critical for C5a binding have been conserved between these species. Sequence comparison of C5aR from multiple species permits conserved elements of the ligand binding sites to be elucidated.

Nucleotide sequence analysis of a human monoclonal antibody 22-13 reactive with lung tumor-associated antigen

A human monoclonal antibody (HuMAb) 22-13 (IgG1, kappa) recognizes a cytoplasmic antigen associated primarily with human lung tumors. This study reports the primary nucleotide and deduced amino acid sequences of the rearranged heavy and light chains of the HuMAb 22-13. This HuMAb uses a VH gene member of the V(H)Ia gene family, 51P1 and is productively rearranged with a D-D fusion product of the D(LR)2 and D(XP)2 germ line DH genes and the germ line JH3 gene. HuMAb 22-13 Vkappa belongs to the kappa light chain variable subgroup IIIb family and appears to be derived from the Humkv325 germ line gene and is rearranged with a germ line Jkappa5 gene. The results reveal that production of a HuMAb 22-13 is achieved by rearrangement of the 51P1/Humkv325 germ line variable region gene combination, associated with the autoimmune repertoire and that HuMAb 22-13 has a striking sequence homology to rheumatoid factors (RFs) of the Wa idiotypic family. HuMAb 22-13 and Wa RFs have in common V(H)Ia and VkappaIIIb gene segments, but use different DH, JH and Jkappa gene segments. However, in spite of this structural similarity, HuMAb 22-13 does not display rheumatoid factor activity. Taken together with the reported findings, these data indicate the representation of the shared usage of highly homologous variable region genes in entirely different humoral immune responses in the human system.

Loss of serotonin-containing neurons in the raphe of patients with myotonic dystrophy: a quantitative immunohistochemical study and relation to hypersomnia

Hypersomnia occurs frequently in patients with myotonic dystrophy (MyD). We performed a quantitative immunohistochemical study of serotonin (5-HT)-containing neurons linked to hypersomnia in the dorsal raphe nucleus (DRN) and the superior central nucleus (SCN) in 8 patients with MyD, 5 of whom showed hypersomnia, and in 12 age-matched controls. The densities of 5-HT neurons in the DRN and the SCN were significantly lower in MyD patients with hypersomnia than in MyD patients without hypersomnia and controls. These data suggest that the loss of 5-HT neurons of the DRN and the SCN is associated with the presence of hypersomnia in MyD.

Cloning and characterization of rat C3a receptor: differential expression of rat C3a and C5a receptors by LPS stimulation

The anaphylatoxin C3a, generated during complement activation, is a factor known to mediate various inflammatory reactions. The human C3a receptor (C3aR) was recently cloned and identified to be a member of the G-protein-coupled receptor family. C3aR is characterized by seven transmembrane domains including a large second extracellular loop that appears to be a unique feature of this receptor. Here we report the isolation of the rat C3aR clone and confirm that the isolated cDNA coded for rat C3aR based on C3a binding analysis to stably transfected cells. Northern blot analysis of rat C3aR revealed expression in various tissues, similar to that of human C3aR but dissimilar to rat C5aR. We found that expression of rat C3aR in various tissues did not increase significantly after LPS injection, whereas rat C5aR expression is greatly increased. These results suggest that expression of C3aR and C5aR is independently regulated in rat cells and tissues.

[Stress-buffering effects of perceived social supports from family members and friends: a comparison of college students and middle-aged adults]

This study investigated perceived social support, emotional as well as instrumental, from family members and friends, and examined their stress-buffering effects on depression in college students and middle-aged adults in Japan. For both samples, family members were relatively more important sources of instrumental support, whereas friends were primarily perceived as emotional support providers. No gender differences were found for the middle-aged adults, but as in previous studies, women in the college sample perceived more support for them than men. A series of hierarchical regression analyses with support by stress interaction terms revealed distinctive patterns of support effects on depression for men and women of each sample. Characteristics of perceived social support in each sample were described, and overall results suggested that it is essential in social support research to take the meanings of supportive relationship into consideration, in the context of social and developmental factors of the samples under study.

Effects of football training on ventilatory and gas exchange kinetics to sinusoidal work load

The purpose of this study was to evaluate the effects of football training on maximal oxygen uptake (VO2max), ventilatory threshold (VT) and kinetics of ventilation and gas exchange variables to sinusoidal work load. The sinusoidal work load during cycling exercise was varied from 30 watts to 60% of VO2max (60% VO2max) with a period of 2 min. O2 uptake (VO2), CO2 output (VCO2), minute ventilation (VE) and heart rate (HR) were measured on a breath-by-breath basis using a computer system. Training periods were continued for 9 months. Six males who had no football experience were performed in which VO2max, VT, and the kinetics of each variable were measured for 3-month intervals (PRE, TR.3, TR.6, and TR.9). They usually underwent football training, such as sprint and strength training for 2-3 hours day-1, 6 days week-1. Mean VO2max was significantly increased at TR.3 and TR.6. VT was also significantly increased during the training period. The amplitude of VO2, VCO2, VE, and HR responses during sinusoidal exercise unchanged during the training period. Phase shifts to work load in VO2 and HR responses did not significantly change during the 9 months, but the phase shift in VCO2 and VE responses significantly continued increasing as the training intervals progressed. These results suggest that football training does not significantly affect the development of the kinetics of VO2 and HR during submaximal exercise, but that it dramatically increases VO2max and VT values.

Intracytoplasmic inclusion bodies of the substantia nigra in myotonic dystrophy. Immunohistochemical observations

We recently reported a significantly higher incidence of intracytoplasmic inclusion bodies (IIBs) of the substantia nigra in patients with myotonic dystrophy (MyD) than in age-matched controls. The changes are, per se, not specific, since a small percentage of disease and normal controls also showed similar inclusions. To elucidate the pathological significance of the inclusion in MyD, we studied immunohistochemical characteristics of IIBs of the substantia nigra in eight patients with MyD. Many IIBs showed moderately intense immunoreactivity for ubiquitin, microtubule-associated protein (MAP) 1 and MAP 2. However, the IIBs did not react with any of the following: anti-neurofilament protein antibodies (Abs) (68, 160 and 200 kDa), anti-neuron-specific enolase antibody (Ab), anti-tau Ab, anti-tubulin Abs (alpha and beta), anti-paired helical filament Ab, anti-actin Ab, anti-phosphorylated epitope of neurofilaments Ab, anti-synaptophysin Ab, anti-myelin basic protein Ab, anti-actin Ab and anti-glial fibrillary acidic protein Ab. Our results suggest that IIBs of the substantia nigra in MyD are related to an alteration of neuronal cytoskeleton metabolism affecting microtubular proteins in conjunction with activation of ubiquitin proteolytic systems.

Analysis of the posture control system under fixed and sway-referenced support conditions

To delineate the relative roles of each of the feedback sensors in the posture control system such as the visual, vestibular, and proprioceptive sensors, an identification technique was applied to measurements of antero-posterior sway angeles of the body and ankle moments under the following conditions: standing on a fixed support with eyes open (ox), standing on a fixed support with eyes closed (cx), standing on a sway-referenced support with eyes open (os), and standing on a sway-referenced support with eyes closed (cs). Frequency response functions from the sway angle to the ankle moment were calculated. Gain and phase characteristics for conditions (os) and (cs) were similar to those of Nashner's vestibular model in the high-frequency range, which shows that the vestibular system may be dominant. The gain was higher under condition (cx) than under (ox). Judging from the phase characteristics, this was probably due to increased weighting of the proprioceptive sensor over the vestibular sensor. There was a tendency for gain to increase as balance tasks became more demanding.

Dynamics of respiratory response to sinusoidal work load in humans

The present study was undertaken to investigate possible distortion in responses of respiratory variables including O2 uptake (VO2), CO2 output (VCO2), and ventilation (VE) to sinusoidal work load, and to find out whether the conventional transfer models were applicable to analyze the dynamics of these variables. Six healthy subjects performed exercise for 32 min on a bicycle ergometer with electro-magnetic braking. The work load was varied sinusoidally between 30 W and 60% of maximum O2 uptake (VO2max) during periods from 1 to 16 min. The respiratory variables were measured on a breath-by-breath basis with a mass spectrometer and a computer system. The responses of VO2, VCO2, and VE to sinusoidal work load were not completely sinusoidal in form but were somewhat distorted, forming saw-tooth waves with steeper down-slopes during periods of 4-16 min, but this distortion was not observed at 1 min or 2 min periods. However, the results could be approximately described by a first-order model without or with time delay. Time constants of the first-order model without time delay were 46 sec for VO2, 62 sec for VCO2, and 73 sec for VE, respectively. We also found a close relationship between the time constants of VO2 and VCO2 and VO2max. These results suggested that exponential functions may be applied and are expected to yield valid results in assessing physical fitness, although the control of ventilatory and gas exchange in exercise does show non-linear characteristics.

Biometeorological studies on urban climate

Urban-biometeorology, i.e., biometeorological study on the urban climate is regarded as both old and/or new science. Studies on two topics are reviewed: the thermal or chemical impact of urban climate on human health, and the relation between urban climate and vegetation.

cDNA cloning and characterization of rat C5a anaphylatoxin receptor

Activation of the complement cascade plays an essential role in the early stages of inflammation. C5a and its receptor are particularly active in anaphylaxis. To determine the pathological roles played by C5a and C5a receptor (C5aR) in rats, we cloned C5aR cDNA and analyzed distribution of its mRNA in various organs including lung from an LPS-stimulated rat. Furthermore, we generated a polyclonal antiserum which specifically recognizes rat C5aR, as confirmed by its specific interaction with cells transfected with rat C5aR cDNA.

Nonlinearity identified by neural network models in Pco2 control system in humans

The nonlinearity included in the PCO2 control system in humans is evaluated using the degree of nonlinearity based on a difference of residuals. An autoregressive moving average (ARMA) model and neural networks (linear and nonlinear) are employed to model the system, and three types of network (Jordan, Elman and fully interconnected) are compared. As the Jordan-type linear network cannot approximate respiratory data accurately, the other two types and the ARMA model are used for the evaluation of the nonlinearity. The results of the evaluation indicate that the linear assumption for the PCO2 control system is invalid for three subjects out of seven. In particular, strong nonlinearity was observed for two subjects.

Respiratory variability in R-R interval during sinusoidal exercise

The R-R interval varies with the cycles of respiration. The response of the variability in the R-R interval with respiration was examined during sinusoidal cycle exercise in 12 healthy young male subjects. Work rate varied sinusoidally between 30 W and 60% maximal oxygen uptake for an 8-min period. The higher the heart rate (HR), the smaller was the magnitude of the variation in R-R interval with respiration (delta RR). When HR increased with an increase in exercise intensity, however, delta RR tended to decrease more markedly at lower HR. On the other hand, since delta RR generally increased linearly during the decrease in HR with a reduction in exercise intensity, delta RR was greater during decreases in HR than during increases in HR at a similar HR. These results suggest that the contribution of the withdrawal of cardiac parasympathetic activity to increases in HR with increases in exercise intensity during sinusoidal exercise were greater at lower HR, and that the cardiac parasympathetic system was more activated during HR decreases than during HR increases at the same HR. From our findings it would seem that such complex parasympathetic HR regulaltion during sinusoidal exercise, which depends on the level of HR and the direction of the change in HR, may be influenced by factors other than the parasympathetic system, such as the cardiac sympathetic system.

Exercise-induced change in beta-adrenergic receptor number in lymphocytes from trained and untrained men

This study was undertaken to clarify whether beta-adrenergic receptor (beta-AR) translocation from intracellular sites to the cell surface contributes to an increase in the number of beta-AR in lymphocytes from trained and untrained men after exercise. Nine trained and 9 untrained subjects performed exercise on a bicycle ergometer until exhaustion. The number of beta-AR in the cell surface (beta-AR(surface)) and intracellular sites (beta-AR(intra)) was determined at rest and after maximal exercise by measuring the binding of the radioligand 125I-iodocyanopindolol in the presence or absence of hydrophilic (CGP-12177A) or lipophilic (propranolol) unlabeled ligands. The number of beta-AR(surface) increased after exercise from 1,524.4 +/- 321.4 to 3,432.6 +/- 503.3 sites/cell (p < 0.01), whereas that of beta-AR(intra) decreased from 356.2 +/- 85.7 to 190.3 +/- 60.2 sites/cell (p < 0.05). The isoproterenol-stimulated cAMP production per 1 x 10(6) lymphocytes after exercise was significantly higher than that at rest. However, the cAMP production per single beta-AR(surface) tended to be lower after exercise. No differences between the trained and untrained subjects were found in beta-AR numbers or intracellular cAMP levels. These findings demonstrate that maximal exercise induces the translocation of beta-AR from intracellular sites to the cell surface in human lymphocytes. However, this translocation accounts for only 10% of the increase in total cellular beta-AR, suggesting that other mechanisms are predominant and contribute substantially to the increase in beta-AR(surface).