Role of Calcium Loading in Early Afterdepolarizations Generated by Cs+ in Canine and Guinea Pig Purkinje Fibers

Ca²⁺-Loading and EAD. introduction: Our previous observations indicate that the Na²⁺:Ca²⁺ exchange current (I_Na:Ca) plays an important role in early afterdepolarizations occurring at more negative Vm (L-EAD). The purpose of these studies was to examine the role of Ca²⁺-loading, which stimulates I_Na:Ca, in generation of L-EAD. Methods and Results: Purkinje strands and preparations of ventricular myocardium from dogs and guinea pigs were superfused with oxygenated physiologic buffer solutions at 37°C, To induce EADs, [K⁺]₀ was reduced to 2.0 to 3.0 mM and [Cs⁺]₀, (3.6 to 4.0 mM) was added at slow rates of ≤ 0.3 Hz. Isometric contraction in canine Purkinje strands and guinea pig papillary muscles doubled in 1-hour exposure to Cs⁺ and low [K⁺]₀ at slow rates, and the uptake of ⁴⁵Ca²⁺ was approximately doubled after 30 minutes. Forty-three percent of Purkinje fibers developed L-EAD after a latent period of 17 to 123 minutes of exposure. Ouabain (0.2 μM) suppressed LEAD within 10 minutes reversibly. Ca²⁺-loading (low [Na⁺]₀ or high [Ca²⁺]₀ for 5 to 10 minutes before exposure to Cs⁺, low [K⁺]₀, and slow rates resulted in rapid development of L-EAD in all preparations during subsequent exposure. In Ca²⁺-loaded preparations, delayed afterdepolarizations (DADs) as well as L-EADs developed. Conclusion: Reduction of K⁺ currents with Cs⁺, low [K⁺]₀, and slow rates induced L-EAD in a fraction of Purkinje fibers after a latent period during which Ca²⁺-loading of the sarcoplasmic reticulum occurred, while fibers preloaded with Ca²⁺ developed L-EAD rapidly and uniformly. These findings indicate that Ca²⁺-loading is a critical condition for the development of L-EAD. Early suppression of L-EAD by ouabain suggests a dependence of L-EAD on low [Na⁺]₁. These findings implicate I_Na:Ca in the generation of L-EAD.     

Nightguard Vital Bleaching of Tetracycline-Stained Teeth: 54 Months Post Treatment

Abstract: Purpose: The purpose of this longitudinal whitening study was to determine the stability, post-treatment side effects, and patient satisfaction after 6 months of active treatment of tetracycline-stained teeth with 10% carbamide peroxide at 0 and 54 months post treatment.
Materials and Methods: Twelve patients who completed the study (80%) were contacted and asked to participate in a survey concerning their whitening experience. Subjects were asked whether there had been any change in the shade of their teeth after treatment, and if they had experienced any side effects that they believed were treatment-related. Eight of the twelve patients underwent clinical examination.
Results: Ten patients (83%) reported no obvious shade change or only a slight darkening not noticed by others. Two (17%) reported a slight darkening that is probably noticeable by other people, but no one reported moderate darkening or significant darkening back to original shade. All respondents (n = 12) denied having to have a crown or root canal that they believed was treatment-related. Examiners who compared preoperative and post-treatment photographs and Vita shade values were in agreement with the patients' perceptions of shade change. The degree of improvement was significant for both the immediate (0 mo) and the 54-month post-treatment comparison with the pretreatment shade (p < .005 and p < .01 respectively).     

Adrenergic Induction of Delayed Afterdepolarizations in Ventricular Myocardial Cells: β Induction and α Modulation

Adrenergic Afterdepolarizations in Ventricular Cells. Introduction: The purpose of these studies was to expose canine multicellular ventricular endocardial preparations and disaggregated myocytes to adrenergic agonists and antagonists, and to investigate the generation of delayed afterdepolarizations and triggered action potentials. Methods and Results: We used multicellular preparations and disaggregated myocytes from canine ventricles. The threshold concentration for induction of delayed afterdepolarizations in isolated myocytes for norepinephrine was between 1 × 10^?8 M and 5 × 10^?5 M, with 50% of the cells showing delayed afterdepolarizations at 4.3 × 10^?8 M. Higher concentrations of epinephrine are required with 50% of the cells responding to 8.3 × 10^?8 M. The threshold concentrations for induction of delayed afterdepolarizations in myocardial cells of multicellular preparations were an order of magnitude higher. Delayed afterdepolarizations could not be induced in Purkinje fibers with concentrations up to 10^?4 M with norepinephrine. Adrenergic delayed afterdepolarizations were inhibited promptly by reduction of pO₂ in superfusate that was equilibrated with N₂ (95%) in place of O₂. The amplitudes of adrenergic delayed afterdepolarizations and the propensity to triggered action potentials were inversely related to cycle length down to the shortest cycle length tested (330 msec). Adrenergic delayed afterdepolarizations were induced by isoproterenol but not by α-adrenergic agonists (methoxamine or phenylephrine). They were inhibited by a β antagonist (propranolol) but not by α antagonists (prazosin or yohimbine). Delayed afterdepolarizations induced by isoproterenol were inhibited by α agonists (methoxamine or phenylephrine). The α-adrenergic inhibitory effects on β-adrenergic delayed afterdepolarizations could be reversed by prazosin, but not by yohimbine. Conclusions: We conclude the natural catecholamines norepinephrine and epinephrine generate delayed afterdepolarizations in myocardial cells, but not in Purkinje cells, by activating β receptors, but activation of α₁ receptors inhibits adrenergic delayed afterdepolarizations. Individual myocytes exhibit widely varying sensitivities for induction of adrenergic delayed afterdepolarizations, but some cells respond to concentrations similar to those that may exist in vivo. Therefore, sympathetic activation in vivo may generate delayed afterdepolarizations, triggered action potentials, and arrhythmias.     

THE VARIETIES OF SELECTIONAL EXPERIENCE IN BEHAVIORAL GENETICS

“There appears to be no character-morphogenetic, behavioral, physiological, or cytological-that cannot be selected in Drosophila.” R. Lewontin (1974)     

RACIAL DIFFERENCES IN CLINICALLY LOCALIZED PROSTATE CANCERS OF BLACK AND WHITE MEN

Purpose

Tumor grade, deoxyribonucleic acid (DNA) ploidy, proliferation, p53 and bcl-2 expression were examined in clinically localized prostate cancers of black and white American men to learn whether these features showed racial differences.

Materials and Methods

A total of 117 prostate cancers (43 black and 74 white patients) obtained at radical prostatectomy for clinically localized disease were assigned Gleason scores by a single pathologist. Enzymatically dissociated nuclei from archival prostate cancers were examined by DNA flow cytometry using propidium iodide staining and the multicycle program to remove debris and sliced nuclei and to perform cell cycle analysis. For immunostaining after microwave antigen retrieval we used a DO-1/DO-7 monoclonal antibody cocktail for p53 and the clone 124 antibody for bcl-2.

Results

Significantly more black than white men had Gleason score 7 tumors. The DNA ploidy distribution of Gleason 6 or less tumors was similar for both races. As anticipated, the ploidy distribution of higher grade prostate cancer in white men was more abnormal but, unexpectedly, this was not found for higher grade prostate cancer in black men. No significant racial differences were found in S phase fractions, p53 or bcl-2 immunopositivity. However, for prostate cancer in black men there was a significant association between bcl-2 immunopositivity and higher S-phase fractions.

Conclusions

The aggressive prostate cancers of black men may be characterized by the 2 features of high proliferation and a block to programmed cell death.     

Pregnancy Alterations Following Xenobiotic-Induced Delays in Ovulation in the Female Rat

Chlordimeform [N'-(4-chloro-o-tolyl)-N,N-dimethylformamidine]has been shown to cause a 1-day delay in the surge of luteinizinghormone (LH) in ovariectomized, steroid-primed female rats,presumably through its ability to block CNS -noradrenergic receptorsand consequently CNS regulation of anterior pituitary function.In the present study, we determined whether a chlordimeform-induceddelay in the ovulatory surge of LH would alter pregnancy outcomein intact females. Chlordimeform (50 mg/kg) or sodium pentobarbital(35 mg/kg), as a positive control, was administered in orderto delay ovulation 24 (1-day delay) or 48 hr (2-day delay).Females were then housed with proven fertile males on the eveningof proestrus (0-day delay group), the following evening (1-daydelay group), or the evening after that (2-day delay group).The number of receptive females in each group, the mean lordosisquotient, and the number of sperm-positive females in each groupwere recorded. All females were killed on Gestation Day 20.The number of pregnant females in the 1- or 2-day delay groupswas reduced with both chlordimeform and pentobarbital. Also,delaying ovulation for 1 or 2 days with either compound resultedin a significant reduction in the number of live pups presenton Gestation Day 20 and a decrease in the number of implantationsites. Litter size was not affected if the females were matedon the same day that treatment was administered (0-day delay).Pentobarbital did not alter the proportion of females showingsexual behavior or the mean lordosis quotient in the 0- and1-day delay groups, although fewer 1-day females were spermpositive. The number of sexually active and sperm-positive femaleswas reduced in the 2-day pentobarbital-delayed group. However,the lordosis quotient of those that were sexually active wasnot different than that of control. Similarly, in CDF-treatedgroups, the proportion of females showing sexual activity wasreduced in the 0- and 2-day delayed groups. In contrast, sexualbehavior was lower in the 0-day delayed females when tested2 hr after lights out. These females did eventually mate, however,as confirmed by the high incidence of sperm positive smearsthe following morning. The number of sperm positive femaleswas lower in both the 1- and 2-day chlordimeform-induced delaygroups. Thus, brief exposures to compounds such as formamidinepesticide chlordimeform will result in not only a delay in breedingbut, more importantly, a significant reduction in litter size.     

Low HL—A2 Frequency and Periodontitis1

The frequency of HL-A2 was significantly low (21%) in patients with periodontitis when compared to controls who were free of periodontal disease (61%). The effect was most pronounced in females in whom HL-A2 was present in 12.5% (2 out of 16). This finding suggests that genes controlling susceptibility to microbial agents may be linked to the HL-A LOCUS.     

DIFFERENTIAL NEURAL CREST CELL ATTACHMENT AND MIGRATION ON AVIAN LAMININ ISOFORMS

A number of laminin isoforms have recently been identified and proposed to exert different functions during embryonic development. In the present study, we describe the purification and partial characterization of several isoforms isolated from chick heart and gizzard, and provide data on the molecular mechanisms underlying the interaction of avian neural crest cells with these molecules in vitro. Laminins extracted from heart and gizzard tissues were separated by gel filtration and purified to homogeneity by sequential lectin and immunoaffinity chromatography by utilizing monoclonal antibodies directed against the avian α2, β2 and γ1 laminin chains. The sodium dodecyl sulfate—polyacrylamide gel electrophoresis (SDS—PAGE) banding pattern of the polypeptide complexes obtained and immunoblotting with polyclonal antisera allowed the identification of Laminin-2 (α2β1γ1), Laminin-4 (α2β2γ1), and laminins comprising the β1, β2 and γ1 chains associated with a shorter α chain which, in SDS—PAGE, co-migrate with the β/γ complex in the 200 kDa region. These latter laminins, which are here arbitrarily denoted Laminin-αχ (heart tissue) and Laminin-G (gizzard tissue), are somewhat distinct in their apparent molecular weight, are differentially associated with nidogen, and appear as “T”-shaped particles similar to Laminin-6 and Laminin-7 when analyzed by transmission electron microscopy following rotary shadowing. In contrast, the avian Laminin-2 and Laminin-4 isoforms exhibit the characteristic cruciform shape described previously for their mammalian counterparts. Isolated neural crest cells differentially attached and migrated on these laminin isoforms, showing a clear preference for Laminin-G. Similarly to the EHS Laminin-1, neural crest cells recognized all avian isoforms through their α1β1 integrin, shown previously to be the primary laminin-binding receptor on these cells. Neural crest cell interaction with the avian laminins was dependent upon maintenance of the secondary and tertiary structure of the molecules, as shown by the marked reduction in cell attachment and migration upon disruption of the α-helical coiled-coil structure of their constituent chains. The results demonstrate that different laminin isoforms may be differentially involved in the regulation of neural crest cell migration and suggest that this regulation operates through interaction of the cells with a structurally conserved cell binding site recognized by the α1β1 integrin. Copyright © 1996. Published by Elsevier Science Ltd.