Regulation of glomerular basement membrane collagen expression by LMX1B contributes to renal disease in nail patella syndrome

Basement membrane (BM) morphogenesis is critical for normal kidney function. Heterotrimeric type IV collagen, composed of different combinations of six alpha-chains (1-6), is a major matrix component of all BMs (ref. 2). Unlike in other BMs, glomerular BM (GBM) contains primarily the alpha 3(IV) and alpha 4(IV) chains, together with the alpha 5(IV) chain. A poorly understood, coordinated temporal and spatial switch in gene expression from ubiquitously expressed alpha 1(IV) and alpha 2(IV) collagen to the alpha 3(IV), alpha 4(IV) and alpha 5(IV) chains occurs during normal embryogenesis of GBM (ref. 4). Structural abnormalities of type IV collagen have been associated with diverse biological processes including defects in molecular filtration in Alport syndrome, cell differentiation in hereditary leiomyomatosis, and autoimmunity in Goodpasture syndrome; however, the transcriptional and developmental regulation of type IV collagen expression is unknown. Nail patella syndrome (NPS) is caused by mutations in LMX1B, encoding a LIM homeodomain transcription factor. Some patients have nephrosis-associated renal disease characterized by typical ultrastructural abnormalities of GBM (refs. 8,9). In Lmx1b(-/-) mice, expression of both alpha(3)IV and alpha(4)IV collagen is strongly diminished in GBM, whereas that of alpha1, alpha2 and alpha5(IV) collagen is unchanged. Moreover, LMX1B binds specifically to a putative enhancer sequence in intron 1 of both mouse and human COL4A4 and upregulates reporter constructs containing this enhancer-like sequence. These data indicate that LMX1B directly regulates the coordinated expression of alpha 3(IV) and alpha 4(IV) collagen required for normal GBM morphogenesis and that its dysregulation in GBM contributes to the renal pathology and nephrosis in NPS.

Operation for acute type A aortic dissection in octogenarians: is it justified?

BACKGROUND

With the progressive aging of Western populations, cardiac surgeons are faced with treating an increasing number of elderly patients. Controversy exists as to whether the expenditure of health care resources on the growing elderly populations represents a cost-effective approach to resource management. The potential to avoid surgery in patients with little chance of survival and poor quality of life would spare unnecessary suffering, reduce operative mortality, and enhance the use of scarce resources.

METHODS

We reviewed the records of 24 consecutive patients aged 80 years or older (mean age 83 years, range 80-93 years) who underwent operations for acute type A dissection from 1985 through 1999. No patient with acute type A dissection was refused surgery because of age or concomitant disease. Seventeen patients were men. Preoperatively, none of the patients was moribund, although 66% had hemodynamic instability and 41% experienced cerebral ischemia. All patients had one or more associated pathologic conditions. Hospital mortality and morbidity models, based on our overall experience with 197 patients operated on for acute type A aortic dissection during the period of the study, were developed by means of multivariate logistic regression with preoperative and intraoperative variables used as independent predictors of outcome.

RESULTS

Overall hospital mortality was 83%. Intraoperative mortality was 33%. All patients who survived the operation had one or more postoperative complications. Mean hospital stay was 37 days with a total of 314 days in the intensive care unit (average 19 days, median 17 days). None of the survivors (4 patients) discharged from the hospital was able to function independently and their survival at 6 months was 0%. Statistical analysis of the overall experience with operations for type A acute aortic dissection confirmed that age in excess of 80 years is the most important independent patient risk factor associated with 30-day mortality and morbidity.

CONCLUSIONS

Operations for acute type A dissection performed on octogenarians involve increased hospital mortality and morbidity. Short-term survival is unfavorable and is associated with a poor quality of life. Without additional corroborative studies to endorse the present findings, the use of age as a parameter to limit access of patients to expensive medical resources remains an unsubstantiated concept. In the context of acute type A aortic dissection, however, the hypothesis that older patients should be denied such a complicated surgical intervention to conserve resources is supported by the presented data.

cDNA cloning, characterization and chromosome mapping of the gene encoding human cartilage associated protein (CRTAP)

We have recently isolated and characterized cDNA clones coding for a novel developmentally regulated avian and mouse embryo protein, CASP for Cartilage Associated Protein. Here we describe the isolation and characterization of the gene coding for the human CASP. The comparison of the putative human and mouse protein sequences with the chick sequence revealed an overall high identity (89% and 51%, respectively). Homology search with known DNA and protein sequences showed that CASPs are related to two mammalian nuclear proteins. Here we demonstrate definitively that CASPs are distinct from these nuclear proteins. However, sequence comparison analyses suggest that all of these proteins belong to a new family. In all human tissues examined two CASP mRNA species were detected, whereas a single mRNA and three mRNAs were found in chick and mouse, respectively. The human CASP gene (CRTAP) was assigned to chromosome 3p22 by fluorescence in situ hybridization.

LMX1B transactivation and expression in nail-patella syndrome

Lmx1b, a member of the LIM homeodomain protein family, is essential for the specification of dorsal limb fates at the zeugopodal and autopodal level in vertebrates. We and others have shown that a skeletal dysplasia, nail-patella syndrome (NPS), results from mutations in LMX1B. While it is a unique mesenchymal determinant of dorsal limb patterning during vertebrate development, the mechanism by which LMX1B mutations generate the NPS phenotype has not been addressed at a transcriptional level or correlated with its spatial pattern of gene expression. In this study, in situ hybridizations of Lmx1b on murine limb sections reveal strong expression in dorsal mesenchymal tissues (precursors of muscle, tendons, joints and patella) and, interestingly, also in anterior structures of the limb, explaining the anterior to posterior gradient of joint and nail dysplasia observed in NPS patients. Transfection studies showed that both the LIM domain-interacting protein, LDB1, and the helix-loop-helix protein, E47/shPan1, can regulate LMX1B action. While co--transfections of E47/shPan1 with LMX1B result in a synergistic effect on reporter activity, LDB1 down-regulated LMX1B-mediated transactivation irrespective of E47/shPan1. Mutant LMX1B proteins containing human mutations affecting each of the helices or the N-terminal arm of the homeodomain abolished transactivation, while LIM B and truncation mutations retained residual activity. These mutations fail to act in a dominant-negative manner on wild-type LMX1B in mixing studies, thereby supporting haploinsufficiency as the mechanism underlying NPS pathogenesis.

Overexpression of p53 and bcl-2 proteins and the presence of HPV infection are independent events in head and neck cancer

The expression of p53 and bcl-2 proteins by immunohistochemistry and the identification of human papillomavirus (HPV) infection by a non-isotopic polymerase chain reaction (PCR)based method were investigated in 30 patients with head and neck cancer. Ten cases were HPV-positive (33%), mostly as double or multiple infections by high- or intermediate-risk types. Twenty-one patients were p53-positive (70%), 9/10 with HPV-positive tumours and 12/20 with HPV-negative tumours; this difference was not statistically significant. Only four cases were bcl-2-positive, irrespective of the presence of either HPV or p53. No correlation was found between these biological factors and tumour stage, differentiation grade, and alcohol or tobacco use. Our findings indicate that p53 is involved in the majority of cases, bcl-2 is rare, and high-risk HPV could play a key role, especially in tumours of tongue and tonsil. In conclusion p53 and bcl-2 protein expression and the presence of HPV infection are independent events in these malignancies.

Physical state and expression of human papillomavirus in laryngeal carcinoma and surrounding normal mucosa

Epidemiologic and biomolecular evidence suggests that human papillomavirus (HPV) infection may be associated with the development of head and neck cancers. To clarify the role of HPV in larynx carcinoma, 25 patients were studied for the presence of viral DNA, possible virus integration into the cellular genome, and viral expression both in neoplastic tissues and in neighbouring normal mucosa. Twelve of 25 patients with neoplasia (48%) showed negative results for HPV sequences, and 13 (52%) showed positive results. Among the latter group of patients, seven were HPV-16 positive, five were HPV-6, and one was HPV-45. No multiple infections were detected. The physical status of the HPV genome was analysed by three methods: polymerase chain reaction (PCR), bidimensional agarose gel electrophoresis, and in situ hybridisation. Viral integration into the host genome occurred in 43% of cases of HPV-16 and in 20% of cases of HPV-6. Viral RNA expression was detected by reverse transcription-PCR only in HPV-16-positive tumours. The pattern of expression was consistent with an active role of HPV in cellular transformation. In conclusion, the present work suggests that HPV infection may be involved in some cases of laryngeal carcinoma. However, the transformation mechanisms might be different from those currently accepted for anogenital cancers.

Human papillomavirus in head and neck carcinomas: prevalence, physical status and relationship with clinical/pathological parameters

The association of human papillomavirus (HPV) infection to head and neck squamous cell carcinomas was evaluated in 66 patients affected by tumours of the oral cavity (n = 38), the tonsil (n = 4), the pharynx (n = 2), and the larynx (n = 22). HPV DNA was detected by PCR-based assays, recognizing late and early genes. Twenty-four cases were HPV infected (36.4%), mostly by high and/or intermediate risk types. HPV 16 was integrated in 7/12 positive tumours without site-specificity. HPV infection was not related to age, gender, tumour stage, differentiation grade, and use of alcohol and/or tobacco. The findings indicate that HPV infection may be related to a proportion of head and neck carcinomas but its association is not as clear as that found in cervical cancer.

Fetal distress increases interleukin-6 and interleukin-8 and decreases tumour necrosis factor-alpha cord blood levels in noninfected full-term neonates

OBJECTIVE

To assess the influence of fetal distress on interleukin-1beta, interleukin-6, interleukin-8 and on tumour necrosis factor-alpha blood levels in noninfected full-term neonates.

STUDY DESIGN

In a multicentre prospective study, cord blood samples were obtained at time of delivery from 234 noninfected full-term neonates for the purposes of measuring serum levels of interleukin-1beta, interleukin-6, interleukin-8 and tumour necrosis factor-alpha using immunoassays. Women were classified into four groups according to the mode of delivery (vaginal delivery or caesarean section) and the presence or absence of fetal distress. The role of labour was also investigated.

RESULTS

No significant relationship was found between cytokine cord blood levels and the mode of delivery. Fetal distress was associated with an increase in interleukin-6 (P = 0.01) and interleukin-8 (P < 0.001) levels, and a decrease in tumour necrosis factor-alpha (P < 0.001). Labour was also associated with a significant increase in interleukin-6 and interleukin-8 cord blood levels (P = 0.01 and P < 0.001, respectively).

CONCLUSION

Fetal distress and labour were each associated with elevated interleukin-6 and interleukin-8 cord blood levels in noninfected full term neonates while only fetal distress was associated with decreased tumour necrosis factor-alpha levels.

Retromolar trigone tumors: evaluation by magnetic resonance imaging and correlation with pathological data

The aim of this study was to evaluate the diagnostic accuracy of magnetic resonance (MR) images to establish both the T stage and the relationships between the tumors and the surrounding structures in retromolar trigone tumors. Twenty-two patients with squamous cell carcinoma of the retromolar trigone were examined by MR with a superconductive scanner operating at 1.5T. The study was performed with spin-echo (SE) T1 and T2 and short SE T1 sequences (TR 180 ms, TE 15 ms) after the administration of 0.2 mmol/kg of gadolinium-DTPA (Gd-DTPA). The mandible was studied with SE T1 weighted sequences and GE sequences. The results were compared with the pathological data on the T stage (TNM classification) and the involvement of the surrounding structures. A positive correlation was found in 19 of the 22 patients with an accuracy of 86%. In one patient, the lesion was classified as T1 by MR which, at surgery, resulted being T4, given the infiltration of the cortical mandible (this infiltration was too limited). In another, the MR showed a T4 lesion because of the presence of low signal intensity in the mandibular marrow with enhancement after the Gd-DTPA injection without cortical erosion, while pathological data revealed a T2 lesion (this signal intensity was secondary to inflammation). In another case, the lesion was classified as T1 by MR which, at surgery, proved to be a T2 lesion. In assessing the involvement of the surrounding structures. MR showed a high accuracy, specificity and sensitivity (> 90%). Five false positive cases were observed: in two because of infiltration of the masseter muscle and in the other three, because of infiltration to the pterigoid muscle, mandible and tonsillar bed, respectively, due to the close contact between the tumors and the surrounding structures. Only one false negative case was observed with infiltration of the mandibular marrow. In evaluating the low signal intensity of the mandibular marrow, the accuracy of MR was 87% the specificity 77% and the sensitivity 100%. In one case, perineural spread along the mandibular nerve was found. In conclusion, MR proved to be highly accurate to study the T stage and examine the relationships between the surrounding structures in cases of retromolar trigone tumors.

cDNA cloning, characterization and chromosome mapping of Crtap encoding the mouse cartilage associated protein

Recently we have isolated and characterized a cDNA coding for a novel developmentally regulated chick embryo protein, cartilage associated protein (CASP). Here we describe the isolation and characterization of the cDNAs coding for the mouse CASP. Comparison of the mammalian putative protein sequence with the chick sequence shows a very high identity overall (51%); in particular the chick protein is homologous to the half amino terminus of the mouse protein. Furthermore, the comparison of the CASP cDNA sequence with sequences of the genebank database confirms our hypothesis that the CASP genes belong to a novel family that also includes genes encoding for some nuclear antigens. In all mouse tissues examined three CASP mRNAs species are detected, whereas in chick tissues a single mRNA is present. Immunohistochemistry studies show that the protein is expressed in all mouse embryonic cartilages. The mouse cartilage associated protein gene (Crtap) was assigned to chromosome 9F3-F4 by fluorescence in situ hybridization.

Study of some components of the cytoskeleton in muscular disorders with nonspecific cytoplasmic bodies

To gain a better understanding of the mechanisms involved in the formation of cytoplasmic bodies (CBs), the immunohistochemical and biochemical features of muscle samples with nonspecific CBs were compared to those previously described by our group in cytoplasmic body myopathy (CBM), a congenital disease in which specific CBs are found. Accordingly, we studied nonspecific CBs found in the muscle biopsies of 15 patients with the following diseases: peripheral neuropathy (n = 5), polymyositis (n = 3), myotonic dystrophy (n = 2), sarcoidosis (n = 1), inclusion body myositis (n = 1), hereditary inclusion body myopathy (n = 1), hypothyroidism (n = 1), and muscle atrophy in a patient with multiple brain infarctions (n = 1). Nonspecific inclusions were stained at their periphery by anti-desmin but not by anti-dystrophin antibodies, except in the case of hypothyroidism in which immunostaining was observed with both antibodies. Biochemical studies showed normal amounts of desmin and phosphorylation pattern (the latter data are available for only four patients) as compared to control specimens. Our results differ from those previously reported in CBM, in which CBs were stained by both antidesmin and anti-dystrophin antibodies and in which a hyperphosphorylation of desmin was found. Hypothyroidism is, thus, the only disease in which nonspecific CBs show the same immunostaining pattern as specific CBs from CBM patients. These findings indicate that CBs may result from different mechanisms, and that one of these mechanisms may be shared by CBM and hypothyroidism.

Evaluation of the ratio of cerebral blood flow to cerebral blood volume as an index of local cerebral perfusion pressure

Local cerebral perfusion pressure (CPP), a crucial parameter that should allow a better assessment of the haemodynamic compromise in cerebrovascular diseases, is not currently measurable by non-invasive means. Experimental and clinical studies have suggested that the regional ratio of cerebral blood flow to cerebral blood volume (CBF:CBV), as measured by PET, represents an index of local CPP in focal ischaemia. The present study was designed to evaluate further the reliability of the CBF:CBV ratio during manipulations of CPP by deliberately varying mean arterial pressure (MAP) in the anaesthetized baboon. Cortical CBF, CBV, cerebral metabolic rate for oxygen (CMRO2) and oxygen extraction fraction were measured by PET using the (15)O steady-state technique in 10 anaesthetized baboons. Five baboons (Group A) underwent four PET examinations at different levels of MAP: base line (101 +/- 6 mmHg) followed by moderate hypotension (58 +/- 3 mmHg) and, in a separate experiment, minor hypotension (72 +/- 3 mmHg) followed by profound hypotension (34 +/- 5 mmHg). Trimetaphan was used to lower MAP to minor and moderate levels while profound hypotension was achieved by the combined effects of trimetaphan and lower-body negative pressure. Five other baboons (Group B) were subjected to hypertension (121 +/- 2 mmHg) induced by metaraminol and were compared with their base line state (81 +/- 10 mmHg). While CBF displayed significant changes with varying MAP, i.e. decrease and increase with hypotension and hypertension, respectively (-11% from base line to moderate hypotension compared with -20%, from minor to profound hypotension and +31% from base line to hypertension), CBV was more variable and did not significantly change, except with profound hypotension when the increase was significant (+13%). The CBF:CBV ratio decreased significantly at all stages of hypotension (-21 and -31%) and was significantly increased during hypertension (+30%). Importantly, the CBF:CBV ratio demonstrated a significant correlation with MAP (rho = 0.78, Spearman's rank correlation coefficient, P < 0.01). No major changes in CMRO2 were noted during either hypotension or hypertension. Our results demonstrate that, under physiological conditions, cortical CBF:CBV is significantly correlated with CPP, itself a function of MAP. In the investigated range of MAP, the relationships between CBF:CBV and MAP appear to be linear. These findings further argue for the reliability of CBF:CBV as an index of CPP in situations where increases or decreases of MAP without superimposed changes in cerebrovascular tone are encountered, and they confirm the potential usefulness of this regional ratio for clinical investigations and management in cerebrovascular diseases.

High frequency of IgG antagonizing follicle-stimulating hormone-stimulated steroidogenesis in infertile women with a good response to exogenous gonadotropins

OBJECTIVE

To investigate the presence of FSH-blocking IgG in infertile women.

DESIGN

Retrospective study. Sera from patients and controls were processed for IgG purification, and purified IgG were tested at various concentrations for their ability to inhibit the recombinant human FSH-induced P production in vitro by human granulosa cells.

SETTING

Departments of Endocrinology, and Obstetrics and Gynecology, University of Caen.

PATIENT(S)

Fifty-seven infertile women including 14 women with premature ovarian failure (POF), 29 women with a poor response to IVF-ET, and 14 women with a good response to IVF-ET. Controls consisted of 22 healthy age-matched women.

INTERVENTION(S)

IVF-ET allowed human granulosa cell pooling and culture for FSH bioassay.

MAIN OUTCOME MEASURE(S)

Inhibition by purified IgG of the in vitro recombinant human FSH-induced P production by human granulosa cells.

RESULT(S)

Blocking IgG were identified in only 3 of 14 POF and in 2 of 29 women with a poor response to IVF-ET. In contrast, IgG from women with a good response to IVF-ET inhibited significantly P production, and blocking IgG were detected in 85% women with a good response to IVF-ET.

CONCLUSION(S)

This study identified FSH-blocking IgG in a high proportion of women with a good response to IVF-ET. The significance of this remains questionable.

Cartilage associated protein (CASP) is a novel developmentally regulated chick embryo protein

A subtracted cDNA library was generated to identify cDNAs specific for chondrocyte mRNAs preferentially expressed at the hypertrophic stage with respect to early differentiation stages. The characterization of a cDNA isolated from this library that hybridizes with a 1.8 kb mRNA is described here. This mRNA is expressed at extremely low levels in dedifferentiated chondrocytes cultured in adherent conditions, at very low levels in differentiating chondrocytes and at very high levels in hypertrophic chondrocytes cultured in suspension conditions. In the developing chick embryo this mRNA is detectable in RNAs extracted from several other tissues besides cartilage. The described cDNA contains a complete open reading frame coding for a polypeptide of about 33 kDa. Homology searches with known cDNA and protein sequences have revealed that the chicken protein is related to the amino-terminal half of two mammalian nuclear antigens. By immunohistochemistry with specific rabbit antisera a strong signal was detected in the cartilage extracellular matrix of selected regions of the developing skeleton. Because of this localization of the antigen we named this protein cartilage associated protein (hereafter referred to as CASP).

Comparative quantitation of cerebral blood volume: SPECT versus PET

Quantification of cerebral blood volume (CBV) measured by SPECT has been used for evaluation of cerebral hemodynamics in patients with cerebrovascular diseases. The accuracy of such quantification, however, has not been validated with PET.

METHODS

CBV was assessed using SPECT and in vitro 99mTc-labeled red blood cells and PET with the 15O steady-state inhalation method and C15O. In 23 patients with carotid artery disease, we measured hemispheric (including cortical and subcortical areas) CBV, and in 11 patients, we measured regional CBV in small cortical regions. We further evaluated the interhemispheric and inter-regional asymmetry of CBV with both methods.

RESULTS

Quantitative values of both hemispheric and regional CBV measured by SPECT were significantly correlated with those measured by PET in the same patients. There was a significant correlation between the side-to-side asymmetry of CBV for both methods.

CONCLUSION

This study demonstrates usefulness and the accuracy of SPECT for quantitative CBV assessment in comparison with the less widely available PET procedures.

Effects of indomethacin on cerebral blood flow and oxygen metabolism: a positron emission tomographic investigation in the anaesthetized baboon

The aim of this study was to clarify the controversy about the effects of indomethacin on the coupling of cerebral blood flow (CBF) to cerebral oxygen metabolism (CMRO2). CBF, blood volume (CBV), oxygen extraction fraction (OEF) and CMRO2 were measured by positron emission tomography (PET) in five anaesthetized baboons before and during an i.v. administration of indomethacin (bolus 20 mg/kg followed by perfusion 10 mg/kg.h). Administration of indomethacin resulted in a marked and homogenous decrease of CBF in every region analysed (-28% to -40%) and a moderate reduction in CBV (-8% to -16%). In contrast, CMRO2 displayed a small increase in thalamus and pons (+10% and +13%, respectively). OEF increased greatly in all structures studied (+59% to +96%). These findings show that the potent cerebrovascular effects of indomethacin are not related to a decrease in CMRO2 as measured through the use of PET.

[Isolation rooms in the psychiatric environment]

To date, there has been no survey concerning psychiatric isolation rooms in France. We conducted a mail survey in 1993 involving all adult psychiatric care catchment areas covering the French departments. The survey revealed an estimated number of 1560 isolation rooms. Isolation rooms were considered as absolutely necessary in all the departments but also as an unsatisfactory solution by one-third of them. Isolation rooms were usually small and poorly adapted to efficient patient surveillance. Furthermore, equipment was often inadequate, particularly for noise and fire protection. A serious accident (fire, suicide, escape) was reported by large number of departments. The rooms were used for agitated psychotic (84%) and psychopathic (16) people. Although requested by the physician, but also in some cases by the patient, conditions of use and design of isolation rooms may be dangerous both for the patient and the nursing staff. Financial investment devoted to isolation rooms varies greatly and there is no specific control over the number of installation. Construction must comply with precise specifications defined in co-ordination with the experts involved.

Postprandial lipoprotein metabolism in normotriglyceridemic non-insulin-dependent diabetic patients: influence of apolipoprotein E polymorphism

Non-insulin-dependent diabetes mellitus (NIDDM) is associated with postprandial lipoprotein clearance defects that are correlated with the fasting hypertriglyceridemia widely observed in NIDDM patients. The aim of this study was to determine if such postprandial disturbances are found in NIDDM patients strictly normotriglyceridemic in the fasting state, and if the apolipoprotein E (apo E) polymorphism influences postprandial metabolism of intestinally derived lipoproteins. The vitamin A-fat loading test was used in 18 normotriglyceridemic NIDDM patients and seven normotriglyceridemic obese controls, and postprandial triglyceride (TG) and retinyl palmitate (RP) concentrations were evaluated in total plasma, and in the chylomicron (Sf > 1,000) and nonchylomicron (Sf < 1,000) fractions isolated by ultracentrifugation. NIDDM patients exhibited an amplified response of both TG and RP as compared with obese controls in the three fractions. Incremental TG response to the oral fat load was strongly correlated with fasting TG level (r = .80, P < .0001) in the whole study population. Postprandial lipoprotein profiles were distinguished in NIDDM patients according to apo E phenotype: despite normal fasting TG levels in E3/3 (n = 6), E2/3 (n = 6), and E3/4 (n = 6), postprandial RP response was twofold to threefold higher in E2/3 and E3/4 patients than in the common E3/3 phenotype. Contrasting lower postprandial TG increment and lower fasting and postprandial high-density lipoprotein (HDL) and HDL3 cholesterol levels were observed in E3/4 versus E3/3 patients, possibly reflecting modifications in lipid content of the postprandial lipoproteins driven by a differential lipid transfer activity depending on apo E isoform. These data indicate an enhanced postprandial lipemia in normotriglyceridemic NIDDM patients, and demonstrate the influence of apo E polymorphism on their lipoprotein clearance. Postprandial alterations of lipoprotein remnants may thus accelerate atherogenesis even in normotriglyceridemic NIDDM patients.

Interaction of nonylguanidine with the sodium channel

Alkyl and aromatic guanidines interact strongly with the tetrodotoxin (TTX)- receptor site in eel electroplaque membranes, showing competition with TTX. That these guanidines could be useful as highly reversible small molecular weight blockers of Na+ currents is therefore suggested. We have investigated the mechanisms of interaction of one of these derivatives, nonylguanidine, by studying its effects on Na+ currents in squid giant axons using voltage clamp techniques. Although nonylguanidine competed with TTX for binding to eel electroplaque membrane fragments (Ki = 1.8 X 10(-5) M), it reversibly blocked both inward and outward Na+ currents in intact axons only if applied to the interior. In axons with the Na+ inactivation removed by papain nonylguanidine produced a time-dependent block very similar to that reported for strychnine and pancuronium. The reduction of steady-state currents in these axons was also voltage-dependent, with increasing block observed with increasing step depolarization. These results suggest that nonylguanidine binds to a site accessible from the axoplasmic side of the channel, simulating Na+ inactivation in papain-treated axons and competing with the normal inactivation process in untreated axons. The competition between internal nonylguanidine and external TTX may result from perturbation by the positively charged nonylguanidine of the TTX-binding site from within the channel itself.

Effect of denervation on the permeability of acetylcholine-activated channels to organic cations

Experiments were perfomed on chronically denervated frog sartorius muscles to determine the permeability of the acetylcholine-activated channels to organic cations. The membrane voltage response to bath-applied acetylcholine was measured with the moving electrode when the muscles were bathed in normal Ringer and in Ringer in which all of the Na+ had been replaced with an organic cation. The magnitude of the maximum voltage response was used to estimate the permeability of the channel to the organic cation. These results were compared with those which have been reported for innervated frog sartorius muscles (Maeno, Edwards, and Anraku, 1977). It is concluded that the permeability to a wide range of organic cations is virtually identical for the extrajunctional channels which develop following denervation and the channels with are localized at the junctional region of innervated muscles.