mCCDcl1 cells show plasticity consistent with the ability to transition between principal and intercalated cells.

The cortical collecting duct of the mammalian kidney plays a critical role in the regulation of body volume, sodium pH, and osmolarity and is composed of two distinct cells types, principal cells and intercalated cells. Each cell type is detectable in the kidney by the localization of specific transport proteins such as aquaporin 2 (Aqp2) and epithelial sodium channel (ENaC) in principal cells and V-ATPase B1 and connexin 30 (Cx30) in intercalated cells. mCCDcl1 cells have been widely used as a mouse principal cell line on the basis of their physiological characteristics. In this study, the mCCDcl1 parental cell line and three sublines cloned from isolated single cells (Ed1, Ed2, and Ed3) were grown on filters to assess their transepithelial resistance, transepithelial voltage, equivalent short circuit current and expression of the cell-specific markers Aqp2, ENaC, V-ATPaseB1, and Cx30. The parental mCCDcl1 cell line presented amiloride-sensitive electrogenic sodium transport indicative of principal cell function; however, immunocytochemistry and RT-PCR showed that some cells expressed the intercalated cell-specific markers V-ATPase B1 and Cx30, including a subset of cells also positive for Aqp2 and ENaC. The three subclonal lines contained cells that were positive for both intercalated and principal cell-specific markers. The vertical transmission of both principal and intercalated cell characteristics via single cell cloning reveals the plasticity of mCCDcl1 cells and a direct lineage relationship between these two physiologically important cell types and is consistent with mCCDcl1 cells being precursor cells.

Practical application of cellular bioenergetics to the care of aged skin.

In human skin fibroblasts in vitro, procollagen-1 and NAD(+)/NADH were reduced in three strains of adult fibroblasts compared with neonatal fibroblasts. The levels of both procollagen-1 and NAD(+)/NADH were increased in the adult fibroblasts by treatment for 24 (NAD energy) or 48 h (procollagen-1) with a complex containing niacinamide, Pal-KTTKS peptide and an olive oil fatty acid derivative (Olivem(®)), especially in combination with a natural extract from dill (Lys'lastine V(®)). In one of the adult fibroblast strains evaluated, these changes in procollagen-1 and NAD(+)/NADH in response to the complex of bioactives were in parallel with increased expression of mRNA biomarkers related primarily to dermal matrix and basement membrane structure, including COL1A1, COL3A1, COL5A1, COL14A1, ELN and LOXL2, in addition to SOD2, NAMPT and TGFBR3; MMP1 was decreased in expression. In general, these mRNA biomarker effects were maintained or boosted by the addition of Lys'lastine V, particularly at 1%, and were similar to the fold changes in mRNA expression in neonatal compared with adult fibroblasts. These results indicate that the complex of niacinamide, Pal-KTTKS and Olivem, especially with addition of Lys'lastine V, increases the NAD(+)/NADH bioenergy level of adult skin fibroblasts in parallel with increased expression of skin structure biomarkers in vitro to levels similar to those in younger fibroblasts. Thus, niacinamide, Pal-KTTKS, Olivem and Lys'lastine V are promising bioactive candidates for inclusion in cosmetic formulations.

Identification of Grf1 on mouse chromosome 9 as an imprinted gene by RLGS-M.

Normal mammalian development requires a diploid combination of both haploid parental genomes. Uniparental disomy for certain segments of specific chromosomes results in aberrant development or prenatal lethality, indicating that the parental genomes have undergone modifications during gametogenesis. These modifications result in parent-of-origin specific expression for some genes, a phenomenon called genomic imprinting. Recent work with DNA methyltransferase deficient mice showed that differential methylation is the probable basis of the imprinted character of several genes. Screening for endogenous imprinted loci using restriction landmark genomic scanning with methylation sensitive enzymes (RLGS-M) identified eight imprinted RLGS (Irigs) candidate loci. Molecular analysis of the genomic region of one of the loci (Irigs2) resulted in the discovery of the paternally imprinted U2afbp-rs gene within a previously identified imprinted region on mouse chromosome 11 (refs 5, 7). This paper describes the characterisation of a novel imprinted RLGS-M locus, Irigs3, on mouse chromosome 9 (ref. 6). Within this locus we identified the Grf1 (also called Cdc25Mm) gene, which is homologous to the RAS-specific guanine nucleotide exchange factor gene, CDC25, in Saccharomyces cerevisiae. Grf1 is located about 30 kb downstream of the methylation imprinted site, identified by RLGS-M, and shows paternal allele specific expression in mouse brain, stomach and heart. Our results indicate that imprinting may have a role in regulating mitogenic signal transduction pathways during growth and development.

Transgenic approaches to modification of cell and tissue function.

The past 18 months have seen rapid advances in the use of transgenic techniques for elucidating cellular mechanisms. The modification of gene, cellular and tissue function has been enhanced by developments in the use of antisense and ribozyme constructs, and by improvements in strategies for cell ablation and homologous recombination.

Development of a highly sensitive ELISA for aldosterone in mouse urine: validation in physiological and pathophysiological states of aldosterone excess and depletion.

BACKGROUND: Clinical studies have established aldosterone as a critical physiological and pathophysiological factor in salt and water homeostasis, blood pressure control and in heart failure. Genetic and physiological studies of mice are used to model these processes. A sensitive and specific assay for aldosterone is therefore needed to monitor adrenocortical activity in murine studies of renal function and cardiovascular diseases. METHODS: Antibodies against aldosterone were raised in sheep as previously described. HRP-Donkey-anti-sheep IgG enzyme tracer was produced in our laboratory using the Lightning-Link HRP technique. Aldosterone ELISA protocol was validated and optimised to achieve the best sensitivity. The assay was validated by analysing the urine of mice collected under various experimental conditions designed to stimulate or suppress aldosterone in the presence of other potentially interfering steroid hormones. RESULTS: Cross-reactivity with the steroids most likely to interfere was minimal: corticosterone=0.0028%, cortisol=0.0006%, DOC=0.0048% except for 5alpha-dihydro-aldosterone=1.65%. Minimum detection limit of this ELISA was 5.2 pmole/L (1.5 pg/mL). The validity of urinary aldosterone ELISA was confirmed by the excellent correlation between results obtained before and after solvent extraction and HPLC separation step (Y=1.092X+0.03, R(2)=0.995, n=54). Accuracy studies, parallelism and imprecision data were determined and all found to be satisfactory. Using this assay, mean urinary aldosterone levels were (i) approximately 60-fold higher in females than males mice; (ii) increased 6-fold by dietary sodium restriction; (iii) increased 10-fold by ACTH infusion and (iv) reduced by >60% in Cyp11b1 null mice. CONCLUSION: We describe an ELISA for urinary aldosterone that is suitable for repeated non-invasive measurements in mice. Female aldosterone levels are higher than males. Unlike humans, most aldosterone in mouse urine is not conjugated. Increased levels were noted in response to dietary sodium restriction and ACTH treatment. The sensitivity of the assay is sufficient to detect suppressed levels in mouse models of congenital adrenal hyperplasia.

Health-related quality of life in college students with and without childhood-onset asthma.

OBJECTIVE: The current study investigated whether differences existed in health-related quality of life between individuals who self-identified as having childhood-onset asthma and individuals without a chronic illness. Additionally, the relationship between perceived illness intrusiveness and illness uncertainty to health-related quality of life was explored. METHODS: College undergraduates at least 18 years of age who self-identified as having childhood asthma were randomly matched by age and gender to healthy control participants. Participants completed a demographic form, the Mishel Uncertainty in Illness Scale-Community Form, the Illness Intrusiveness Scale, and the SF-36 Health Survey, a measure of health-related quality of life. RESULTS: Participants with asthma had significantly lower scores on the total and mental health-related quality of life scales than did healthy control subjects. There were no significant differences between self-identified participants with asthma and matched healthy control subjects on physical health-related quality of life scales. Illness intrusiveness was not related to either the physical (e.g., physical functioning, general health) or mental health-related quality of life. Higher levels of illness uncertainty were significantly related to higher levels of mental health-related quality of life (e.g., vitality, mental health). In addition, participants with asthma scored significantly lower than healthy controls on the social functioning and role-emotional subscales. CONCLUSION: The current study adds to the extant literature by examining the relationships between illness intrusiveness, illness uncertainty, and health-related quality of life among a young adult population. College students with asthma appear to be at risk for diminished quality of life compared to a healthy comparison group. Further examination of various domains of health-related quality of life among older adolescents and young adults with childhood asthma is needed.

Cryptic loxP sites in mammalian genomes: genome-wide distribution and relevance for the efficiency of BAC/PAC recombineering techniques.

Cre is widely used for DNA tailoring and, in combination with recombineering techniques, to modify BAC/PAC sequences for generating transgenic animals. However, mammalian genomes contain recombinase recognition sites (cryptic loxP sites) that can promote illegitimate DNA recombination and damage when cells express the Cre recombinase gene. We have created a new bioinformatic tool, FuzznucComparator, which searches for cryptic loxP sites and we have applied it to the analysis of the whole mouse genome. We found that cryptic loxP sites occur frequently and are homogeneously distributed in the genome. Given the mammalian nature of BAC/PAC genomic inserts, we hypothesised that the presence of cryptic loxP sites may affect the ability to grow and modify BAC and PAC clones in E. coli expressing Cre recombinase. We have observed a defect in bacterial growth when some BACs and PACs were transformed into EL350, a DH10B-derived bacterial strain that expresses Cre recombinase under the control of an arabinose-inducible promoter. In this study, we have demonstrated that Cre recombinase expression is leaky in un-induced EL350 cells and that some BAC/PAC sequences contain cryptic loxP sites, which are active and mediate the introduction of single-strand nicks in BAC/PAC genomic inserts.

Demonstration of a mitochondrial DNA-compatible workflow for genetically variant peptide identification from human hair samples.

Hair is an evidentiary sample that typically does not provide sufficient nuclear DNA for forensic analysis. Therefore, state-of-the-art forensic examination for hair samples include subjective microscopic evaluation, mitochondrial DNA (mtDNA) analysis, and more recently, proteomic genotyping that uses protein variation in the form of genetically variant peptides (GVPs) to infer single nucleotide polymorphism (SNP) alleles. Since many cases involve limited sample amounts (approximately 2 cm or less), any additional destructive testing (besides mtDNA) would be excluded. If a mtDNA-compatible protein extraction workflow could be developed, GVPs would provide additional forensic value without sacrificing any portion of the original hair sample. Here, we demonstrate an optimized method that can be used to obtain both whole genome mtDNA and putative GVP profiles from a single limited hair sample. The method involves urea-based extraction of proteins from hair, followed by buffer exchange and protease digestion. Peptides are eluted through a 30 kDa membrane and analyzed using traditional proteomic techniques. DNA is subsequently extracted from the filter and analyzed using whole mt-genome analysis. The method was verified with a range of hair sample types (head, pubic, and arm hair) from a diverse cohort of 22 individuals. Specifically, putative GVP profiles and mtDNA haplotypes concordant with buccal swab samples from the same donor were obtained from 22 individuals. Further, the utility of the method was verified across two different laboratories. The method is applicable for proteomic-based GVP analysis and mt-genome analysis for forensic research applications.

Preliminary report: Surgical outcomes following genitoplasty in children with moderate to severe genital atypia.

INTRODUCTION: Prior studies of outcomes following genitoplasty have reported high rates of surgical complications among children with atypical genitalia. Few studies have prospectively assessed outcomes after contemporary surgical approaches. OBJECTIVE: The current study reported the occurrence of early postoperative complications and of cosmetic outcomes (as rated by surgeons and parents) at 12 months following contemporary genitoplasty procedures in children born with atypical genitalia. STUDY DESIGN: This 11-site, prospective study included children aged ≤2 years, with Prader 3-5 or Quigley 3-6 external genitalia, with no prior genitoplasty and non-urogenital malformations at the time of enrollment. Genital appearance was rated on a 4-point Likert scale. Paired t-tests evaluated differences in cosmesis ratings. RESULTS: Out of 27 children, 10 were 46,XY patients with the following diagnoses: gonadal dysgenesis, PAIS or testosterone biosynthetic defect, severe hypospadias and microphallus, who were reared male. Sixteen 46,XX congenital adrenal hyperplasia patients were reared female and one child with sex chromosome mosaicism was reared male. Eleven children had masculinizing genitoplasty for penoscrotal or perineal hypospadias (one-stage, three; two-stage, eight). Among one-stage surgeries, one child had meatal stenosis (minor) and one developed both urinary retention (minor) and urethrocutaneous fistula (major) (Summary Figure). Among two-stage surgeries, three children developed a major complication: penoscrotal fistula, glans dehiscence or urethral dehiscence. Among 16 children who had feminizing genitoplasty, vaginoplasty was performed in all, clitoroplasty in nine, external genitoplasty in 13, urethroplasty in four, perineoplasty in five, and total urogenital sinus mobilization in two. Two children had minor complications: one had a UTI, and one had both a mucosal skin tag and vaginal mucosal polyp. Two additional children developed a major complication: vaginal stenosis. Cosmesis scores revealed sustained improvements from 6 months post-genitoplasty, as previously reported, with all scores reported as good or satisfied. DISCUSSION: In these preliminary data from a multi-site, observational study, parents and surgeons were equally satisfied with the cosmetic outcomes 12 months after genitoplasty. A small number of patients had major complications in both feminizing and masculinizing surgeries; two-stage hypospadias repair had the most major complications. Long-term follow-up of patients at post-puberty will provide a better assessment of outcomes in this population. CONCLUSION: In this cohort of children with moderate to severe atypical genitalia, preliminary data on both surgical and cosmetic outcomes were presented. Findings from this study, and from following these children in long-term studies, will help guide practitioners in their discussions with families about surgical management.

Differential methylation of the ornithine carbamoyl transferase gene on active and inactive mouse X chromosomes.

Ornithine carbamoyl transferase (Oct) is an X-linked gene which exhibits tissue-specific expression. To determine whether methylation of specific CpG sequences plays a role in dosage compensation or tissue-specific expression of the gene, 13 potentially methylatable sites were identified over a 30-kilobase (kb) region spanning from approximately 15 kb upstream to beyond exon II. Fragments of the Mus hortulanus Oct gene were used as probes to establish the degree of methylation at each site. By considering the methylation status in liver (expressing tissue) versus kidney (nonexpressing tissue) from male and female mice, the active and inactive genes could be investigated on active and inactive X-chromosome backgrounds. One MspI site, 12 kb 5' of the Oct-coding region, was cleaved by HpaII in liver DNA from males but not in kidney DNA from males and thus exhibited complete correlation with tissue-specific expression of the gene. Six other sites showed partial methylation, reflecting incomplete correlation with tissue-specific expression.

Measurement of the microstructural fracture toughness of cortical bone using indentation fracture.

The purpose of this work is to investigate the use of indentation fracture as a method of measuring toughness at the microscale in cortical bone. Indentation fracture employs sharp indenters to initiate cracks, whose length can be used to calculate the toughness of the material. Only a cube corner indenter tip is found to initiate cracks at a suitable size scale for microstructural measurement. Cracks from 7 to 56 microm in length are produced using loads from 0.05 to 3N. Preliminary data predicts rising toughness with increasing crack length (rising R-curve behaviour) at the microscale. This technique provides a new insight into fracture in cortical bone since it allows the investigator to observe mechanisms and measure toughness at a size scale at which in vivo damage is known to exist.

Micromechanical modelling of cortical bone.

Cortical bone is a heterogeneous material with a complex hierarchical microstructure. In this work, unit cell finite element models were developed to investigate the effect of microstructural morphology on the macroscopic properties of cortical bone. The effect of lacunar and vascular porosities, percentage of osteonal bone and orientation of the Haversian system on the macroscopic elastic moduli and Poisson's ratios was investigated. The results presented provide relationships for applying more locally accurate material properties to larger scale and whole bone models of varying porosity. Analysis of the effect of the orientation of the Haversian system showed that its effects should not be neglected in larger scale models. This study also provides insight into how microstructural features effect local distributions and cause a strain magnification effect. Limitations in applying the unit cell methodology approach to bone are also discussed.

Prospective assessment of cosmesis before and after genital surgery.

INTRODUCTION: Little data exist about the surgical interventions taking place for children with disorders of sex development (DSD). Most studies that have evaluated cosmetic outcomes after genitoplasty have included retrospective ratings by a physician at a single center. OBJECTIVE: The present study aimed to: 1) describe frequency of sex assignment, and types of surgery performed in a cohort of patients with moderate-to-severe genital ambiguity; and 2) prospectively determine cosmesis ratings by parents and surgeons before and after genital surgery. STUDY DESIGN: This prospective, observational study included children aged <2 years of age, with no prior genitoplasty at the time of enrollment, moderate-to-severe genital atypia, and being treated at one of 11 children's hospitals in the United States of America (USA). Clinical information was collected, including type of surgery performed. Parents and the local pediatric urologist rated the cosmetic appearance of the child's genitalia prior to and 6 months after genitoplasty. RESULTS: Of the 37 children meeting eligibility criteria, 20 (54%) had a 46,XX karyotype, 15 (40%) had a 46,XY karyotype, and two (5%) had sex chromosome mosaicism. The most common diagnosis overall was congenital adrenal hyperplasia (54%). Thirty-five children had surgery; 21 received feminizing genitoplasty, and 14 had masculinizing genitoplasty. Two families decided against surgery. At baseline, 22 mothers (63%), 14 fathers (48%), and 35 surgeons (100%) stated that they were dissatisfied or very dissatisfied with the appearance of the child's genitalia. Surgeons rated the appearance of the genitalia significantly worse than mothers (P < 0.001) and fathers (P ≤ 0.001) at baseline. At the 6-month postoperative visit, cosmesis ratings improved significantly for all groups (P < 0.001 for all groups). Thirty-two mothers (94%), 26 fathers (92%), and 31 surgeons (88%) reported either a good outcome, or they were satisfied (see Summary Figure); there were no significant between-group differences in ratings. DISCUSSION: This multicenter, observational study showed surgical interventions being performed at DSD centers in the USA. While parent and surgeon ratings were discordant pre-operatively, they were generally concordant postoperatively. Satisfaction with postoperative cosmesis does not necessarily equate with satisfaction with the functional outcome later in life. CONCLUSION: In this cohort of children with genital atypia, the majority had surgery. Parents and surgeons all rated the appearance of the genitalia unfavorably before surgery, with surgeons giving worse ratings than parents. Cosmesis ratings improved significantly after surgery, with no between-group differences.

A comparison of measurements of intracellular Ca by Ca electrode and optical indicators.

Squid giant axons were injected with aequorin or arsenazo III and impaled with a Ca-sensing electrode. The light output of aequorin or the spectrophotometer output when measuring arsenazo was compared with the voltage output of the electrode when the squid axon was depolarized with high-K solutions, when the seawater was made Na-free, or when the axon was tetanized for several minutes. The results from these treatments were that the optical response rose (as much as 50-fold) with all treatments known to increase Ca entry, while the electrode remained unaffected by these treatments. If axons previously subjected to Ca load are treated with electron-transport poisons such as CN, it is known that [Ca]i rises after a time necessary to deplete ATP stores. In such axons one expects a rise of [Ca]i in axoplasm which does not necessarily have to be uniform although the source of such Ca is the mitochondria and these are uniformly distributed in axoplasm. Under conditions of CN application, the optical signals from aequorin or arsenazo and Ca electrode output do rise together when [Ca]i is high, but there is a region of [Ca]i concentration where aequorin light output or arsenazo absorbance rises while electrode output does not. Axons not loaded with Ca but injected with apyrase and vanadate have mitochondria that still retain some Ca and this can be released by CN in a truly uniform manner. The results show that such a release (which is small) can be readily measured with aequorin, but again the Ca electrode is insensitive to such [Ca]i change.

A mechanism for Na/Ca transport.

A model is developed which requires the binding of 4 Na+ to a carrier before a Ca binding site is induced on the opposite side of the membrane. Upon binding Ca, this carrier translocates Na and Ca. The existence of partially Na-loaded but nonmobile forms for the carrier (NaX, Na2X, Na3X) suffices to explain both the activating and the inhibitory effects of Na on the Ca transport reaction. Analytical expressions for Ca efflux and influx in terms of [Na]o, [Na]i, [Ca]o, [Ca]i, and Em are developed for the Na/Ca exchange system at equilibrium; these provide for a quantitative description of Ca fluxes. Under nonequilibrium conditions, appropriate modifications of the flux equations can be developed. These show a dependence of Ca efflux on [Ca]o and of Ca influx on [Ca]i. The large effect of internal ATP on Ca efflux and influx in squid axons, with no change in net Ca flux, can be understood on the single assumption that ATP changes the affinity of the carrier for Na at both faces of the membrane without providing an energy input to the transport reaction.

Calcium measurement in the periphery of an axon.

Aequorin was microinjected into squid giant axons, the axons were stimulated, and the change in light emission was followed. This response was compared with that found when the axon, in addition to being microinjected with aequorin, is also injected with the dye phenol red. Large concentrations of phenol red injected into axons result in a high probability that photons emitted by aequorin, when it reacts with Ca in the core of the axoplasm, will be absorbed before they escape from the axon; photons produced by the aequorin reaction at the periphery of the axoplasm are much less likely to be absorbed. This technique thus favors observing changes in Cai taking place in the periphery of the axon. Stimulation in 50 mM Ca seawater of an aequorin-phenol red-injected axon at 180 s-1 for 1 min produces a scarcely detectable change in Cai; the addition of 2 mM cyanide (CN) to the seawater produces an easily measureable increase in Cai, suggesting that mitochondrial buffering in the periphery is substantial. Making the pH of the axoplasm of a normal axon alkaline with 30 mM NH4+ -50 mM Ca seawater, reduces the resting glow of the axon but results in an even more rapid increase in Cai with stimulation. In a phenol red-injected axon, this treatment results in a measureable response to stimulation in the absence of CN.

Tracer and nontracer potassium fluxes in squid giant axons and the effects of changes in external potassium concentration and membrane potential.

The efflux of labeled and unlabeled potassium ions from the squid giant axon has been measured under a variety of experimental conditions. Axons soaked in sea water containing 42K ions lost radioactivity when placed in inactive sea water according to kinetics which indicate the presence of at least two cellular compartments. A rapidly equilibrating superficial compartment, probably the Schwann cell, was observed to elevate the specific activity of 42K lost from such axons to K-free sea water for a period of hours. The extra radioactive potassium loss from such axons during stimulation, however, was shown to have a specific activity identical within error to that measured in the axoplasm at the end of the experiment. The same was shown for the extra potassium loss occurring during passage of a steady depolarizing current. Axons placed in sea water with an elevated potassium ion concentration (50 mM) showed an increased potassium efflux that was in general agreement with the accompanying increase in membrane conductance. The efflux of potassium ions observed in 50 mM K sea water at different membrane potentials did not support the theory that the potassium fluxes obey the independence principle.

Potassium fluxes in dialyzed squid axons.

Measurements have been made of K influx in squid giant axons under internal solute control by dialysis. With [ATP](i) = 1 microM, [Na](i) = 0, K influx was 6 +/- 0.6 pmole/cm(2) sec; an increase to [ATP](i) = 4 mM gave an influx of 8 +/- 0.5 pmole/cm(2) sec, while [ATP](i) 4, [Na](i) 80 gave a K influx of 19 +/- 0.7 pmole/cm(2) sec (all measurements at approximately 16 degrees C). Strophanthidin (10 microM) in seawater quantitatively abolished the ATP-dependent increase in K influx. The concentration dependence of ATP-dependent K influx on [ATP](i), [Na](i), and [K](o) was measured; an [ATP](i) of 30 microM gave a K influx about half that at physiological concentrations (2-3 mM). About 7 mM [Na](i) yielded half the K influx found at 80 mM [Na](i). The ATP-dependent K influx responded linearly to [K](o) from 1-20 mM and was independent of whether Na, Li, or choline was the principal cation of seawater. Substances tested as possible energy sources for the K pump were acetyl phosphate, phosphoarginine, PEP, and d-ATP. None was effective except d-ATP and this substance gave 70% of the maximal flux only when phosphoarginine or PEP was also present.

Some factors influencing sodium extrusion by internally dialyzed squid axons.

Squid giant axons were internally dialyzed by a technique previously described. In an axon exposed to cyanide seawater for 1 hr and dialyzed with an ATP-free medium, the Na efflux had a mean value of 1.3 pmole/cm(2)sec when [Na](i) was 88 mM, in quantitative agreement with flux ratio calculations for a purely passive Na movement. When ATP at a concentration of 5-10 mM was supplied to the axoplasm by dialysis, Na efflux rose almost 30-fold, while if phosphoarginine, 10 mM, was supplied instead of ATP, the Na efflux rose only about 15-fold. The substitution of Li for Na in the seawater outside did not affect the Na efflux from an axon supplied with ATP, while a change to K-free Na seawater reduced the Na efflux to about one-half. When special means were used to free an axon of virtually all ADP, the response of the Na efflux to dialysis with phosphoarginine (PA) at 10 mM was very small (an increment of ca. 3 pmole/cm(2)sec) and it can be concluded that more than 96% of the Na efflux from an axon is fueled by ATP rather than PA. Measurements of [ATP] in the fluid flowing out of the dialysis tube when the [ATP] supplied was 5 mM made it possible to have a continuous measurement of ATP consumption by the axon. This averaged 43 pmole/cm(2)sec. The ATP content of axons was also measured and averaged 4.4 mM. Estimates were made of the activities of the following enzymes in axoplasm: ATPase, adenylate kinase, and arginine phosphokinase. Values are scaled to 13 degrees C.

Sensitivity of calcium efflux from squid axons to changes in membrane potential.

Squid giant axons were internally dialyzed with a medium free of metabolic substrates but containing 45Ca buffered with EGTA to concentrations of free Ca++ in the range 0.01-230 muM. At (Ca)i of 1.0 muM OR GREATER, Ca efflux was in the range of 1-3 pmol/cm2 s, was dependent on (Na)o and (Ca)o, and was sensitive to membrane potential. At lower (Ca)i, the sensitivity of Ca efflux to membrane potential was greater. Hyperpolarization of the membrane increased, and depolarization decreased Ca efflux over the range of potentials studied (-20 to -100 mV). The maximum sensitivity of Ca efflux to membrane potential was of the order of an e-fold increase in Ca efflux for a 25-mV increase in Em; this sensitivity of Ca efflux to membrane potential was lost if (Na)o was removed and was greatly reduced when (Ca)i was increased to 230 muM.