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C J Henderson

Publications and source records attributed to C J Henderson.

At least 55 records · Page 3Linked to original sources
PubMed1993

Transplacental transfer of polychlorinated biphenyls induces simultaneously the expression of P450 isoenzymes and the protooncogenes c-Ha-ras and c-raf.

At day 15 of gestation, rats were injected with a single i.p. dose of 100, 250 and 500 mg/kg body weight of a mixture of polychlorinated biphenyls (PCBs) (Aroclor 1254). Seven days later, significant increases in maternal and foetal cytochrome P450, cytochrome b5 and cytochrome c (P450) reductase were found. Concomitantly, the metabolism of nitroanisole, aniline, ethoxyresorufin and benzo[a]pyrene was significantly increased, but foetal metabolism of dimethylnitrosamine was not detectable and only marginal increases in the metabolism of aminopyrine and aldrin were seen. In contrast, maternal metabolism of dimethylnitrosamine, aminopyrine and aldrin was measurable, but significant increases were determined only with the latter substrate. Transplacental transfer of PCBs resulted in increased metabolism of substrates catalysed by foetal CYP1A1 and CYP2B1, but there was no evidence for CYP2E1-catalysed reactions. Further measurements show significant increases in foetal and maternal epoxide hydrolase, glutathione-S-transferase and UDP-glucuronyl transferase activities, thus suggesting that treatment with Aroclor 1254 resulted in coordinated increases in foetal and maternal oxidative and post-oxidative drug metabolism. Western blot analysis of microsomal proteins shows the induction of foetal and maternal CYP1A1, CYP1A2, CYP2A1, CYP2B1, CYP3A1 and CYP4A1. In addition, increased expression of CYP2C6 was seen with the mother but not the foetus. Unlike the mother, foetal rats did not express CYP2E1 and the expression of the above-listed P450 isoenzymes was greater in the mother than the foetus. Northern blot analysis shows significant increases in maternal and foetal CYP1A1, CYP1A2 and CYP2B1 mRNA. An increased amount of CYP3A1 mRNA was only seen with the mother, but not the foetus. Treatment of mothers with Aroclor 1254 resulted in reduced CYP2A1, CYP2C7, CYP2E1 and CYP4A1 mRNA. Insignificant differences in the expression of foetal CYP2A1 and CYP4A1 mRNA were found, but in utero exposure to PCBs reduced the amounts of CYP2E1 mRNA and there was no foetal CYP2C7 mRNA transcript. Treatment with Aroclor 1254 increased the expression of the protooncogenes c-Ha-ras and c-raf in the mother and the foetus, but at varying intensities. Pregnancy itself was linked to an increased expression of these protooncogenes. erbA and erbB mRNA was not detected.

Animals↗
PubMed1993

Lactational transfer of 2,4,5,2',4',5'-hexachlorobiphenyl but not 3,4,3',4'-tetrachlorobiphenyl, induces neonatal CYP4A1.

In order to study the lactational transfer of polychlorinated biphenyls, lactating rats were treated with a low dose of either 3,4,3',4'-tetrachlorobiphenyl (TCB), 2,4,5,2',4',5'-hexachlorobiphenyl (HCB) or a combination of TCB and HCB. For comparison, animals were also treated with Aroclor 1254, Lactational transfer of these chemicals resulted in the induction of neonatal hepatic CYP4A haemoproteins, the isozymes induced being dependent on the compound used. CYP4A1 was not detected in control, TCB or HCB/TCB-treated animals, but was induced in neonates when mothers were treated with HCB or Aroclor 1254. In the case of Aroclor 1254, the magnitude of the effect appeared to be dependent on the dose used. CYP4A2 and CYP4A3 were induced in the neonates when mothers were treated with Aroclor 1254 but not with the other agents used. It appears that TCB induces novel members of the CYP4A gene family. The present study provides immunochemical evidence for the ability of congeneric polychlorinated biphenyls to modulate differentially the expression of CYP4A isozymes in lactating mothers and their suckling offspring. These findings further support the potential hazards induced by lactational transfer of inert lipophilic chemicals and exemplify the complexity of the regulation of genes within this gene family.

Animals↗
PubMed1993

1,4-Bis[2-(3,5-dichloropyridyloxy)]benzene, an extremely potent modulator of mouse hepatic cytochrome P-450 gene expression.

We have investigated the effects of TCPOBOP (1,4-bis[2-(3,5- dichloropyridyloxy)]benzene), a potent cytochrome P-450-inducing agent [Poland, Mak, Glover, Boatman, Ebetino and Kende (1980) Mol. Pharmacol. 18, 571-580], on cytochrome P-450 isoenzyme expression in the mouse. Hepatic cytochrome P-450s from several distinct gene families were strikingly induced by a single dose of 75 micrograms of the compound. Northern-blot analysis demonstrated that this induction was almost certainly due to transcriptional activation of the cytochrome P-450 genes. The potency of this inductive effect was further reflected in the finding that cytochrome P-450 levels were still increased 12 weeks after a single injection of 75 micrograms of this compound. Interestingly, the mRNA levels of certain other genes, including those of metallothionein and the mouse major urinary proteins, were also induced. In view of the similarity in the effects of TCPOBOP and the synthetic glucocorticoid dexamethasone on mouse hepatic gene expression, we determined whether TCPOBOP acts through the glucocorticoid receptor. This did not, however, appear to be the case. Experiments with hypophysectomized animals demonstrated that TCPOBOP action was not regulated indirectly via the pituitary. In addition, induction of mouse Cyp2b protein by TCPOBOP in a primary culture of mouse hepatocytes suggests that the compound has a direct action on mouse liver. The above findings demonstrate that TCPOBOP is one of the most potent modulators of cytochrome P-450 gene expression described to date. It is not inconceivable that a single dose of this compound may alter hepatic gene expression for the majority of the lifespan of a mouse.

Animals↗
PubMed1993

High variability of nitrosamine metabolism among individuals: role of cytochromes P450 2A6 and 2E1 in the dealkylation of N-nitrosodimethylamine and N-nitrosodiethylamine in mice and humans.

We undertook this study to answer several questions regarding nitrosamine metabolism. Kinetics of nitrosamine metabolism showed the involvement of at least two enzymes in the dealkylation of N-nitrosodiethylamine (NDEA) and N-nitrosodimethylamine (NDMA) in mouse liver microsomes. Coumarin inhibited both reactions competitively. On the other hand, microsomal coumarin 7-hydroxylase was inhibited by NDMA (Ki 2.7 mM) and NDEA (Ki 0.013 mM). The big difference in the Ki values suggests a higher affinity of NDEA than NDMA to Cyp2a-5 (mouse cytochrome P450coh). A specific antibody against Cyp2a-5 inhibited more of the microsomal NDEA (up to 90%) than NDMA (up to 40%) dealkylation. The converse was true with anti-Cyp2e-1 antibody. These results suggest that the primary substrate for Cyp2a-5 is NDEA and for Cyp2e-1, NDMA. Western blot analysis of human liver microsomes showed a great interindividual variation in the amounts of CYP2A6 (human cytochrome P450coh) and CYP2E1. Also, coumarin 7-hydroxylation and nitrosamine dealkylation varied greatly among individuals. A high correlation (r = 0.93, P < 0.001) was found between NDEA and coumarin metabolism. Both activities were associated with CYP2A6. On the other hand, little or no correlation was found between microsomal CYP2A6 and CYP2E1 or between CYP2E1 and NDEA dealkylation. Immunoinhibition of human microsomal NDEA metabolism by CYP2a-5 antibody varied greatly among individuals (10-90%), suggesting, as in the case of mice, that NDEA is metabolized primarily by CYP2A6, at least in some individuals. Taken together the data suggest that (1) the metabolic activation of nitrosamines in humans varies greatly among individuals; (2) different nitrosamines may partially be metabolized by different cytochrome P450 isozymes; and (3) because of similarities between nitrosamine metabolism in mice and humans, inbred strains of mice would be relevant experimental models for studying nitrosamine activation.

Animals↗
PubMed1993

Expression of P450 isoenzymes during rat liver organogenesis.

1. The expression of P450 isoenzymes in foetal and neonatal hepatic microsomes was determined by measuring the metabolism of marker substrates and by studying the expression of P450 isoenzymes at the protein and mRNA level. 2. Monooxygenase activities were not measurable at day 10 of gestation, but shortly before birth (day 20 of gestation) and thereafter a surge in monooxygenase activities was observed using ethoxyresorufin, aniline, nitroanisole, aminopyrine, dimethylnitrosamine and aldrin as substrates. 3. In contrast, as early as day 10 of gestation, post oxidative drug metabolism was measurable, when assessed for reactions catalysed by UDP-glucuronyltransferase, glutathione S-transferase and epoxide hydrolase. 4. Microsomal proteins isolated from foetal/perinatal rats did not crossreact with antibodies raised to CYP1A1, CYP1A2, CYP2A1, CYP2B1, CYP2E1, CYP3A1 and CYP4A1 at a protein loading of 3 micrograms total protein/well. 5. With the exception of CYP2E1 mRNA and CYP4A1 mRNA there was little evidence to suggest the expression of CYP1A1, CYP1A2 and CYP2A1 mRNA. 6. The mRNA of CYP2B1, CYP2C7 and CYP3A1 was not detectable in foetal/perinatal rat liver extracts at a loading rate of 10 micrograms total RNA. 7. Microsomal proteins isolated from neonatal rats crossreacted with antibodies raised to CYP2C6, CYP2E1, CYP3A1 and CYP4A1, albeit at varying intensities. 8. Concomitantly, CYP2A1, CYP2E1 and CYP4A1 mRNA transcripts were detectable in Northern blot hybridization experiments using neonatal rat liver RNA extracts.

Animals↗
PubMed1993

In vitro metabolism of aflatoxin B1 by normal and tumorous liver tissue from Thailand.

Liver tissues were obtained from 20 liver cancer patients from Thailand, an area where the incidence of this tumour is high and where exposure to aflatoxin occurs. The expression of hepatic cytochrome P450s (P450) and glutathione S-transferase (GST) was examined and this expression was compared to the in vitro metabolism of aflatoxin B1 (AFB1). There was a > 10-fold inter-individual variation in expression of the various P450s including CYP3A4 (57-fold), CYP2B6 (56-fold) and CYP2A6 (120-fold). Microsomal metabolism of AFB1 to AFB1 8,9-epoxide (as measured by AFB1 tris-diol formation) and aflatoxin Q1 (AFQ1), the major metabolite produced, was significantly correlated with CYP3A3/4 expression (P < 0.001) and, to a lesser extent, with CYP2B6 expression (P < 0.01). There was a significantly reduced expression of major P450 proteins in microsomes from liver tumours compared to microsomes from the paired normal liver when analysed by Western immunoblot analysis. The production of AFQ1 and AFB1 tris-diol was almost uniformly reduced in tumours, but interestingly, the production of AFP1 was significantly increased. The immunoreactive expression of the major human classes of cytosolic GSTs (alpha, mu and pi) was also analyzed in normal and tumorous liver tissue. The expression of GSTA (alpha) and GSTM (mu) class proteins was markedly decreased and GSTP (pi) increased in the majority of tumour cytosols compared to normal liver. The cytosolic GST activity (1-chloro-2,4-dinitrobenzene conjugation) was significantly lower in liver tumours compared to normal liver (193 +/- 149 versus 875 +/- 299 nmol/min/mg, P < 0.0001), as was glutathione peroxidase (GPx) activity (cumene hydroperoxide) (26 +/- 23 versus 70 +/- 26 nmol/min/mg respectively, P < 0.005). Ten out of 14 individuals (71%) were homozygous null when genotyped for GSTM1. There was no detectable conjugation of AFB1 8,9-epoxide to glutathione by cytosol either from tumorous or normal liver. Thus, capacity of human cytosols to conjugate reactive AFB1 metabolites to GSH resembled AFB1-sensitive species such as rat, trout and duck rather than resistant species such as mouse and hamster. These data indicate a strong capacity of multiple forms of human hepatic P450s to metabolize AFB1 to both the reactive intermediate AFB1 8,9-epoxide and the detoxification product AFQ1. These results suggest that in view of the lack of significant GST-mediated protection against AFB1 in human liver, variations in expression of hepatic P450, due either to genetic polymorphisms or to modulation by environmental factors, may be important determinants in the risk of liver cancer development in AFB1-exposed populations.

Adolescent↗
PubMed1992

Catalytic activities of human debrisoquine 4-hydroxylase cytochrome P450 (CYP2D6) expressed in yeast.

A 1.57kb BamH1 fragment containing a full-length human debrisoquine 4-hydroxylase cytochrome P450 (CYP2D6) cDNA was inserted into the BglII site of the yeast expression plasmid pMA91 and the resulting recombinant plasmid, PELT1, introduced into Saccharomyces cerevisiae strain AH22. Microsomes prepared from AH22/pELT1 cells gave an absorption maximum at 448 nm and a P450 content of 67 +/- 31 pmol/mg of microsomal protein. No P450 was detectable in microsomes prepared from AH22/pMA91 control cells. A western blot of microsomes prepared from yeast transformed with pELT1 were probed with a monoclonal antibody to CYP2D6 and revealed a strong band with a molecular mass consistent with that of CYP2D6 from human liver microsomes. No corresponding band was observed with microsomes from control yeast transformed with pMA91 alone. Microsomes from AH22/pELT cells showed catalytic activity towards metoprolol (alpha-hydroxylation and O-demethylation, 0.17 and 0.78 nmol/mg protein/h, respectively); and towards sparteine (2- and 5-dehydrogenation, 1.82 and 0.59 nmol/mg protein/h, respectively). The inhibition of metoprolol metabolism by quinidine (Qd) was 200 times more potent than that of quinine (Qn), both for alpha-hydroxylation (Qd IC50 = 0.05 microM; Qn IC50 = 4 microM) and O-demethylation (Qd IC50 = 0.05 microM; Qn IC50 = 4 microM). Negligible metabolism of tolbutamide and S-mephenytoin, substrates of the 2C sub-family, and of p-nitrophenol, a substrate of CYP2E1, was detected, although a trace of the N-deethylated metabolite of lignocaine, thought to be metabolised by CYP3A4, was detected with microsomes from CYP2D6-expressing yeast cells. The results indicate that yeast cells containing human CYP2D6 cDNA express a functionally active form of the enzyme, the immunochemical and catalytic properties of which are consistent with those of human liver.

Cytochrome P-450 CYP2D6↗
PubMed1992

Relative expression of cytochrome P450 isoenzymes in human liver and association with the metabolism of drugs and xenobiotics.

Cytochrome P450s play a central role in the metabolism and disposition of an extremely wide range of drugs and chemical carcinogens. Individual differences in the expression of these enzymes may be an important determinant in susceptibility to adverse drug reactions, chemical toxins and mutagens. In this paper, we have measured the relative levels of expression of cytochrome P450 isoenzymes from eight gene families or subfamilies in a panel of twelve human liver samples in order to determine the individuality in their expression and whether any forms are co-regulated. Isoenzymes were identified in most cases on Western blots based on the mobility of authentic recombinant human cytochrome P450 standards. The levels of the following P450 proteins correlated with each other: CYP2A6, CYP2B6 and a protein from the CYP2C gene subfamily, CYP2E1 and a member of the CYP2A gene subfamily, CYP2C8, CYP3A3/A4 and total cytochrome P450 content. Also, the levels of two proteins in the CYP4A gene subfamily were highly correlated. These correlations are consistent with the relative regulation of members of these gene families in rats or mice. In addition, the level of expression of specific isoenzymes has also been compared with the rate of metabolism of a panel of drugs, carcinogens and model P450 substrates. These latter studies demonstrate and confirm that the correlations obtained in this manner represent a powerful approach towards the assignment of the metabolism of substrates by specific human P450 isoenzymes.

Antibodies↗
PubMed1992

Sexual differentiation and regulation of cytochrome P-450 CYP2C7.

The multigene family of proteins known as the cytochrome P-450-dependent monooxygenases play a central role in the metabolism of hormones and foreign compounds. As part of our studies into the function and regulation of these proteins we have isolated a little studied constitutively expressed isozyme CYP2C7 and have investigated its substrate specificity and mode of regulation. Interestingly the haem of this enzyme in its isolated form is almost 100% in the high spin state. The enzyme was active in the metabolism of a range of model resorufin substrates, but exhibits highest activity towards benzyloxyresorufin. Indeed, this isozyme appears to play a significant role in the metabolism of this substrate in microsomal samples from untreated male rats. Tissue distribution studies indicated that CYP2C7 was expressed in liver, kidney and possibly muscle tissue. Cytochrome P-450 CYP2C7 could not be significantly induced by any of a wide range of known modulators of cytochrome P-450 expression at the mRNA level, however some significant changes in protein expression were observed. Some of the agents used (e.g., diethylnitrosamine and carbon tetrachloride) caused a significant reduction in the expression of this protein. In agreement with other reports where mRNA levels were measured we found that the level of CYP2C7 protein expression was sexually differentiated. Female rats express two to three times the level found in males, the sex difference being reversible by hypophysectomy.

Animals↗
PubMed1992

A nutritional screening test for use in children and adolescents with juvenile rheumatoid arthritis.

Protein-energy malnutrition (PEM) has been demonstrated in about 35% of patients with juvenile rheumatoid arthritis (JRA), but fewer than 8% of children with rheumatic diseases were reported in a national survey to have been seen by a pediatric dietitian. We demonstrate the development of a nutritional screening test for PEM in patients with JRA for use by all health care professionals. Nutritional assessment of 74 patients with JRA was conducted using a standardized 11 variable profile comprised of upper body anthropometric and biochemical measurements. The sensitivity, specificity, predictive values and index of validity were calculated for individual and selected clusters of nutritional variables to predict the need for referral for PEM compared to the independent review by 2 pediatric dietitians to refer or not refer to a dietitian for further evaluation or care. Arm circumference less than or equal to 10th percentile for age and sex matched norms was selected as the screening test for PEM in patients with JRA due to a combination of excellent measurement characteristics (sensitivity 0.80, specificity 0.86, positive predictive value 0.90, negative predictive value 0.73, index of validity 0.88) and ease of measurement.

Adolescent↗
PubMed1991

Evidence that the androgen receptor mediates sexual differentiation of mouse renal cytochrome P450 expression.

We have previously shown that sexual dimorphism in the expression of mouse renal cytochrome P450s is mediated by androgens, probably at a transcriptional level [Henderson, Scott, Yang & Wolf (1990), Biochem. J. 266, 675-681]. In the present study we show that this effect is already observed for most isoenzymes at only 2-3 weeks of age, as is the ability to induce or suppress expression with exogenous testosterone. The testosterone responsiveness did, however, exhibit age- as well as dose-dependency. Intriguingly, the effects of androgen took up to 8 days to become maximized, and the dose of testosterone needed to convert the female into the male phenotype was much higher than the circulating levels normally found in males. Studies using testicular feminized (Tfm) male mice, which carry an androgen receptor defect, showed them to have the female kidney cytochrome P450 phenotype, and these animals were not responsive to testosterone treatment. These data demonstrate the involvement of the androgen receptor in the regulation process. Taken together, our results indicate that the androgen receptor does not interact directly with the P450 genes, but initiates a cascade of events leading to the changes in cytochrome P450 gene expression. Significant differences were observed in the degree of sexual dimorphism in kidney P450 expression in other mammalian species. The significance of these findings in relation to the observed sexual dimorphism in other species is discussed.

Animals↗
PubMed1991

Nutritional aspects of juvenile rheumatoid arthritis.

This article focuses on the factors contributing to increased risk for malnutrition in juvenile rheumatoid arthritis patients, the methods of identifying and treating nutritional problems (including protein-energy malnutrition and obesity), and outlines national statistics demonstrating that the pediatric rheumatic patient population is nutritionally underserved. The dietitian, in conjunction with the interdisciplinary treatment team, should be involved in the initial evaluation of all juvenile rheumatoid arthritis patients to facilitate early detection of nutritional problems and initiate nutritional intervention strategies.

Arthritis, Juvenile↗
PubMed1990

Testosterone-mediated regulation of mouse renal cytochrome P-450 isoenzymes.

We have studied the extent to which mouse renal cytochrome P-450 isoenzymes are sexually differentiated, and the factor(s) regulating this dimorphism. Intriguingly, sex differences were not seen in the expression of a single cytochrome P-450 enzyme, but were observed in the expression of all P-450 isoenzymes detectable, encoded by six gene families or sub-families. This effect was mediated by testosterone, which had the capacity to both induce and repress P-450 gene expression, and which was independent of growth hormone. The changes in protein content were mirrored in all but one case by changes in the levels of mRNA, indicating that these genes contain hormone-responsive elements. These findings are consistent with numerous reports of sex differences in the susceptibility of the mouse kidney to the toxic and carcinogenic effects of drugs and environmental chemicals, many of which are metabolized to cytotoxic products by the cytochrome P-450-dependent mono-oxygenases. These data imply that circulating androgen levels will be an important factor in susceptibility of the kidney to toxic or carcinogenic compounds which require metabolic activation.

Animals↗
PubMed1990

The human horizontal vestibulo-ocular reflex in response to high-acceleration stimulation before and after unilateral vestibular neurectomy.

The normal horizontal vestibulo-ocular reflex (HVOR) is largely generated by simultaneous stimulation of the two horizontal semicircular canals (HSCCs). To determine the dynamics of the HVOR when it is generated by only one HSCC, compensatory eye movements in response to a novel vestibular stimulus were measured using magnetic search coils. The vestibular stimulus consisted of low-amplitude, high-acceleration, passive, unpredictable, horizontal rotations of the head with respect to the trunk. While these so called head "impuses" had amplitudes of only 15-20 degrees with peak velocities up to 250 deg/s, they had peak accelerations up to 3000 deg/s/s. Fourteen humans were studied in this way before and after therapeutic unilateral vestibular neurectomy; 10 were studied 1 week or 1 year afterwards; 4 were studied 1 week and 1 year afterwards. The results from these 14 patients were compared with the results from 30 normal control subjects and with the results from one subject with absent vestibular function following bilateral vestibular neurectomy. Compensatory eye rotation in normal subjects closely mirrored head rotation. In contrast there was no compensatory eye rotation in the first 170 ms after the onset of head rotation in the subject without vestibular function. Before unilateral vestibular neurectomy all the patients' eye movement responses were within the normal control range. One week after unilateral vestibular neurectomy however there was a asymmetrical bilateral HVOR deficit. The asymmetry was much more profound than has been shown in any previous studies. The HVOR generated in response to head impulses directed away from the intact side largely by ampullofugal disfacilitation from the single intact HSCC (ignoring for the moment the small contribution to the HVOR from stimulation of the vertical SCCs), was severely deficient with an average gain (eye velocity/head velocity) of 0.25 at 122.5 deg/sec head velocity (normal gain = 0.94 +/- 0.08). In contrast the HVOR generated in response to head impulses directed toward the intact side, largely by ampullopetal excitation from the single intact HSCC, was only mildly (but nonetheless significantly) deficient, with an average gain of 0.80 at 122.5 deg/sec head velocity. At these accelerations there was no significant improvement in the average HVOR velocity gain in either direction over the following year. These results indicate that ampullopetal excitation from one HSCC can, even in the absence of ampullofugal disfacilitation from the opposite HSCC, generate a near normal HVOR in response to high-acceleration stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Acceleration↗
PubMed1989

Assessment of protein-energy malnutrition in children and adolescents with juvenile rheumatoid arthritis.

The incidence of protein-energy malnutrition (PEM) in juvenile rheumatoid arthritis (JRA) patients referred to a dietitian was compared with PEM in a nonreferred JRA population. One pediatric dietitian evaluated all 28 patients using a standardized, 11-parameter comprehensive nutritional assessment profile. Thirty-six percent (10) were found to have PEM (greater than or equal to 6 of 11 parameters abnormal as defined for this study), 36% (10) had no abnormal parameters, and 28% (8) had one-five abnormal parameters. Seventy percent (7 of 10) of the patients referred to a dietitian had PEM: 17% (3 of 18) of the nonreferred JRA patients had PEM. PEM was found in all onset types of JRA. In the ten patients with PEM, 80% had weight less than 5th percentile, 30% had heights less than 5th percentile, 50% had subnormal visceral proteins, 90% had subnormal somatic proteins, and none showed depletion of subcutaneous fat reserves. The high prevalence of PEM supports the need for greater involvement of pediatric dietitians in the evaluation and treatment of JRA patients.

Adolescent↗
PubMed1988

Analysis of calmodulin acceptor proteins and the influence of calmodulin antagonists on human spermatozoa.

The possible role of calmodulin in regulating a number of calcium-dependent functions exhibited by human spermatozoa was investigated by using the antagonists trifluoperazine and calmidazolium. At high doses both antagonists inhibited the motility of human spermatozoa and induced a concomitant rise in [Ca2+]i and a decline in cAMP. Lower doses of these antagonists, particularly calmidazolium, suppressed the ability of human spermatozoa to generate reactive oxygen species and exhibit sperm-oocyte fusion, without influencing [Ca2+]i, cAMP, or motility. This inhibition of sperm-oocyte fusion was effective even if the spermatozoa were subsequently exposed to A23187, suggesting that calmodulin may regulate this aspect of human sperm function at a point downstream from calcium influx. Both radiolabelling and affinity chromatography techniques were used to detect a number of calcium-dependent and calcium-independent calmodulin acceptor proteins in the human spermatozoon. The major calcium-dependent acceptor proteins exhibited Mr values of 32,000 and 22,000-27,000, respectively, and did not appear to be associated with the sperm plasma membrane.

Calcium↗