The heterogenic nature of troponin T (TnT) isoforms in fast skeletal and cardiac muscle suggests important functional differences. Dynamic features of rat cardiac TnT (cTnT) and rat fast skeletal TnT (fsTnT) reconstituted cardiac muscle preparations were captured by fitting the force response of small amplitude (0.5%) muscle length changes to the recruitment-distortion model. The recruitment of force-bearing cross-bridges (XBs) by increases in muscle length was favored by cTnT. The recruitment magnitude was approximately 1.5 times greater for cTnT- than for fsTnT-reconstituted muscle fibers. The speed of length-mediated XB recruitment (b) in cTnT-reconstituted muscle fiber was 0.50-0.57 times as fast as fsTnT-reconstituted muscle fibers (3.05 vs. 5.32 s(-1) at sarcomere length, SL, of 1.9 microm and 4.16 vs. 8.36 s(-1) at SL of 2.2 microm). Due to slowing of b in cTnT-reconstituted muscle fibers, the frequency of minimum stiffness (f(min)) was shifted to lower frequencies of muscle length changes (at SL of 1.9 microm, 0.64 Hz, and 1.16 Hz for cTnT- and fsTnT-reconstituted muscle fibers, respectively; at SL of 2.2 microm, 0.79 Hz, and 1.11 Hz for cTnT- and fsTnT-reconstituted muscle fibers, respectively). Our model simulation of the data implicates TnT as a participant in the process by which SL- and XB-regulatory unit cooperative interactions activate thin filaments. Our data suggest that the amino-acid sequence differences in cTnT may confer a heart-specific regulatory role. cTnT may participate in tuning the heart muscle by decreasing the speed of XB recruitment so that the heart beats at a rate commensurate with f(min).

Chandra M, Tschirgi ML, Ford SJ, Slinker BK, Campbell KB. Interaction between myosin heavy chain and troponin isoforms modulate cardiac myofiber contractile dynamics. Am J Physiol Regul Integr Comp Physiol 293: R1595-R1607, 2007. First published July 11, 2007; doi:10.1152/ajpregu.00157.2007.-Coordinated expression of species-specific myosin heavy chain (MHC) and troponin (Tn) isoforms may bring about a dynamic complementarity to match muscle contraction speed with species-specific heart rates. Contractile system function and dynamic force-length measurements were made in muscle fibers from mouse and rat hearts and in muscle fibers after reconstitution with either recombinant homologous Tn or orthologous Tn. The rate constants of length-mediated cross-bridge (XB) recruitment (b) and tension redevelopment (k tr) of mouse fibers were significantly faster than those of rat fibers. Both the tension cost (ATPase/tension) and rate constant of length-mediated XB distortion (c) were higher in the mouse than in the rat. Thus the mouse fiber was faster in all dynamic and functional aspects than the rat fiber. Mouse Tn significantly increased b and k tr in rat fibers; conversely, rat Tn significantly decreased b and k tr in mouse fibers. Thus the lengthmediated recruitment of force-bearing XB occurs much more rapidly in the presence of mouse Tn than in the presence of rat Tn, demonstrating that the speed of XB recruitment is regulated by Tn. There was a significant interaction between Tn and MHC such that changes in either Tn or MHC affected the speed of XB recruitment. Our data demonstrate that the dynamics of myocardial contraction are different in the mouse and rat hearts because of sequence heterogeneity in MHC and Tn. At the myofilament level, coordinated expression of complementary regulatory contractile proteins produces a functional dynamic phenotype that allows the cardiovascular systems to function effectively at different heart rates. myofiber dynamics; contraction speed; heart rate THERE IS SUBSTANTIAL PROTEIN sequence heterogeneity among orthologous cardiac myosin heavy chain (MHC) and troponin (Tn) isoforms across different animal species (30). This sequence heterogeneity in regulatory contractile proteins significantly affects myofilament dynamics, as assessed by the force response to muscle length change in constantly activated cardiac myofibers, which exhibits two clearly separable processes (3,5,20,30,35): 1) a relatively fast force dynamic associated with myosin cross-bridge (XB) distortion and 2) a relatively slow force dynamic associated with recruitment of additional XB into force-bearing states. The dynamics of XB distortion are principally determined by the enzymatic kinetics of MHC, and the dynamics of XB recruitment are affected greatly by cooperative interactions between Tn actions and XB cycling kinetics (3, 5, 6, 30).Our group (9) recently showed that differences in troponin T (TnT), a subunit of the Tn regulatory protein complex, affected the slow XB recruitment dynamic (9), whereas a shift f...

The objective of this research was to develop a method to confirm the geographical authenticity of Idaho-labeled potatoes as Idaho-grown potatoes. Elemental analysis (K, Mg, Ca, Sr, Ba, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, S, Cd, Pb, and P) of potato samples was performed using ICPAES. Six hundred eight potato samples were collected from known geographic growing sites in the U.S. and Canada. An exhaustive computational evaluation of the 608 x 18 data sets was carried out using statistical (PCA, CDA, discriminant function analysis, and k-nearest neighbors) and neural network techniques. The neural network classification of the samples into two geographic regions (defined as Idaho and non-Idaho) using a bagging technique had the highest percentage of correct classifications, with a nearly 100% degree of accuracy. We report the development of a method combining elemental analysis and neural network classification that may be widely applied to the determination of the geographical origin of unprocessed, fresh commodities.

How different mutations in cardiac troponin T (cTnT) lead to distinct secondary downstream cellular remodeling in familial hypertrophic cardiomyopathy (FHC) remains elusive. To explore the molecular basis for the distinct impact of different mutations in cTnT on cardiac myocytes, we studied mechanical activity of detergent-skinned muscle fiber bundles from different lines of transgenic (TG) mouse hearts that express wild-type cTnT (WTTG), R92W cTnT, R92L cTnT, and Delta-160 cTnT (deletion of amino acid 160). The amount of mutant cTnT is approximately 50% of the total myocellular cTnT in both R92W and R92L TG mouse hearts and approximately 35% in Delta-160 TG mouse hearts. Myofilament Ca2+ sensitivity was enhanced in all mutant cTnT TG cardiac muscle fibers. Compared with the WTTG fibers, Ca2+ sensitivity increased significantly at short sarcomere length (SL) of 1.9 microm (P < 0.001) in R92W TG fibers by 2.2-fold, in R92L by 2.0-fold, and in Delta-160 by 1.3-fold. At long SL of 2.3 microm, Ca2+ sensitivity increased significantly (P < 0.01) in a similar manner (R92W, 2.5-fold; R92L, 1.9-fold; Delta-160, 1.3-fold). Ca2+-activated maximal tension remained unaltered in all TG muscle fibers. However, tension-dependent ATP consumption increased significantly in Delta-160 TG muscle fibers at both short SL (23%, P < 0.005) and long SL (37%, P < 0.0001), suggesting a mutation-induced change in cross-bridge detachment rate constant. Chronic stresses on relative cellular ATP level in cardiac myocytes may cause a strain on energy-dependent Ca2+ homeostatic mechanisms. This may result in pathological remodeling that we observed in Delta-160 TG cardiac myocytes where the ratio of sarco(endo)plasmic reticulum Ca2+-ATPase 2/phospholamban decreased significantly. Our results suggest that different types of stresses imposed on cardiac myocytes would trigger distinct cellular signaling, which leads to remodeling that may be unique to some mutants.

Approximately 5-10% of cancers are caused by an inherited predisposition. Individuals affected by hereditary cancer are often concerned about transmitting a predisposition to cancer to their children. Preimplantation genetic diagnosis (PGD) is a technology that allows embryos without a deleterious mutation associated with a hereditary cancer syndrome to be identified and implanted. The aim of this study is to assess the knowledge, attitudes, and clinical experience of physicians regarding PGD for hereditary cancer predisposition syndromes. Hereditary Breast and Ovarian Cancer (HBOC) and Familial Adenomatous Polyposis (FAP) are two hereditary cancer syndromes highlighted in this present study. A survey assessing physicians' attitudes, knowledge, and clinical practice was completed by a total of 373 gynecologic oncologists (GYN ONCs) and obstetrics and gynecologists (OB/GYNs). Physicians had a limited knowledge of PGD for hereditary cancer; however, physicians reported PGD was an appropriate option for patients with either HBOC or FAP. Although GYN ONCs were more likely to care for patients with hereditary cancer (P < 0.001), they were less likely than OB/GYNs to refer their patients to a PGD specialist (P = 0.004). While 80% of GYN ONCs and 91% of OB/GYNs would refer patients to a PGD specialist, clinical experience indicates that only 29% actually referred their patients. Since 68% of physicians had incorrect or limited knowledge of PGD for hereditary cancer, there is a need for additional education.

Chemical intolerance is a phenomenon observed in multiple chemical sensitivity (MCS) syndrome, an ill‐defined disorder in humans attributed to exposure to volatile organic compounds. Amplification of symptoms in individuals with MCS resembles the phenomenon of psychostimulant‐ and stress‐induced sensitization in rodents. We have recently tested in rats the hypothesis that repeated chemical exposure produces sensitization of central nervous system (CNS) circuitry. A rat model of MCS in our laboratory has employed several endpoints of CNS function after repeated formaldehyde (Form) exposure (1 h/day × 5 days/week × 4 weeks). Repeated Form exposure produced behavioral sensitization to later cocaine injection, suggesting altered dopaminergic sensitivity in mesolimbic pathways. Rats given repeated Form also demonstrated increased fear conditioning to odor paired with footshock, implicating amplification of neural circuitry guiding fear responding to a conditioned odor cue. Recent studies examining the effects of repeated Form on locomotor activity during each daily exposure showed a decrease in rearing activity after 12‐15 days of Form exposure compared to air‐exposed controls. EEG recordings taken 1 week after withdrawal from daily Form revealed altered sleep architecture. Some of the differences in sleep disappeared after subsequent brief (15 min) challenge with Form the next day. Overall, the findings indicate that repeated low‐level chemical exposure produces behavioral changes that may be akin to those observed in individuals with MCS, such as greater sensitivity to chemicals manifest as increased anxiety upon chemical exposure and altered sleep and/or fatigue. Study of the underlying CNS changes will provide a basis for mechanistically based animal models for MCS.

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Cardiac troponin T (cTnT)is an essential component of the thin filament regulatory unit (RU) that regulates Ca 2+ activation of tension in the heart muscle. Because there is coupling between the RU and myosin crossbridges, the functional outcome of cardiomyopathy-related mutations in cTnT may be modified by the type of myosin heavy chain (MHC) isoform. Ca 2+ activation of tension and ATPase activity were measured in muscle fibres from normal rat hearts containing α-MHC isoform and propylthiouracil (PTU)-treated rat hearts containing β-MHC isoform. Muscle fibres from normal and PTU-treated rat hearts were reconstituted with two different mutations in rat cTnT; the deletion of Glu162 (cTnT E162DEL ) and the deletion of Lys211 (cTnT K211DEL ). α-MHC and β-MHC isoforms had contrasting impact on tension-dependent ATP consumption (tension cost) in cTnT E162DEL and cTnT K211DEL reconstituted muscle fibres. Significant increases in tension cost in α-MHC-containing muscle fibres corresponded to 17% (P < 0.01) and 23% (P < 0.001) when reconstituted with cTnT E162DEL and cTnT K211DEL , respectively. In contrast, tension cost decreased when these two cTnT mutants were reconstituted in muscle fibres containing β-MHC; by approximately 24% (P < 0.05) when reconstituted with cTnT E162DEL and by approximately 17% (P = 0.09) when reconstituted with cTnT K211DEL . Such differences in tension cost were substantiated by the mechano-dynamic analysis of cTnT mutant reconstituted muscle fibres from normal and PTU-treated rat hearts. Our observation demonstrates that qualitative changes in MHC isoform alters the nature of cardiac myofilament dysfunction induced by mutations in cTnT.