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Brunet NM, Marsh NK, Bean CR, Powell ZA. Trust in the police and affective evaluation of police faces: a preliminary study. Front Psychol 2023; 14:1258297. [PMID: 38022938 PMCID: PMC10666740 DOI: 10.3389/fpsyg.2023.1258297] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Accepted: 10/16/2023] [Indexed: 12/01/2023] Open
Abstract
Introduction A study was conducted to investigate if an individual's trust in law enforcement affects their perception of the emotional facial expressions displayed by police officers. Methods The study invited 77 participants to rate the valence of 360 face images. Images featured individuals without headgear (condition 1), or with a baseball cap (condition 2) or police hat (condition 3) digitally added to the original photograph. The images were balanced across sex, race/ethnicity (Asian, African American, Latine, and Caucasian), and facial expression (Happy, Neutral, and Angry). After rating the facial expressions, respondents completed a survey about their attitudes toward the police. Results The results showed that, on average, valence ratings for "Angry" faces were similar across all experimental conditions. However, a closer examination revealed that faces with police hats were perceived as angrier compared to the control conditions (those with no hat and those with a baseball cap) by individuals who held negative views of the police. Conversely, participants with positive attitudes toward the police perceived faces with police hats as less angry compared to the control condition. This correlation was highly significant for angry faces (p < 0.01), and stronger in response to male faces compared to female faces but was not significant for neutral or happy faces. Discussion The study emphasizes the substantial role of attitudes in shaping social perception, particularly within the context of law enforcement.
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Affiliation(s)
- Nicolas M. Brunet
- Department of Psychology, California State University, San Bernardino, San Bernardino, CA, United States
| | - Natalya K. Marsh
- Department of Psychology, California State University, San Bernardino, San Bernardino, CA, United States
| | - Caitlin R. Bean
- Department of Psychology, California State University, San Bernardino, San Bernardino, CA, United States
| | - Zachary A. Powell
- School of Criminology and Criminal Justice of Criminal Justice, California State University, San Bernardino, San Bernardino, CA, United States
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Brunet NM. Face processing and early event-related potentials: replications and novel findings. Front Hum Neurosci 2023; 17:1268972. [PMID: 37954936 PMCID: PMC10634455 DOI: 10.3389/fnhum.2023.1268972] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Accepted: 10/05/2023] [Indexed: 11/14/2023] Open
Abstract
This research explores early Event-Related Potentials (ERPs) sensitivity to facial stimuli, investigating various facial features aimed to unveil underlying neural mechanisms. Two experiments, each involving 15 undergraduate students, utilized a multidimensional stimulus set incorporating race, gender, age, emotional expression, face masks, and stimulus orientation. Findings highlight significant modulations in N170 and P200 amplitudes and latencies for specific attributes, replicating prior research and revealing novel insights. Notably, age-related facial feature variations, facial inversion, and the presence of face masks significantly impact neural responses. Several speculative explanations are proposed to elucidate these results: First, the findings lend support to the idea that the increased N170 amplitude observed with facial inversion is closely tied to the activation of object-sensitive neurons. This is further bolstered by a similar amplitude increase noted when masks (effective objects) are added to faces. Second, the absence of an additional amplitude increase, when inverting face images with face masks suggests that neural populations may have reached a saturation point, limiting further enhancement. Third, the study reveals that the latency deficit in N170 induced by facial inversion is even more pronounced in the subsequent ERP component, the P200, indicating that face inversion may impact multiple stages of face processing. Lastly, the significant increase in P200 amplitude, typically associated with face typicality, for masked faces in this study aligns with previous research that demonstrated elevated P200 amplitudes for scrambled faces. This suggests that obscured faces may be processed as typical, potentially representing a default state in face processing.
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Affiliation(s)
- Nicolas M. Brunet
- Department of Psychology, California State University of San Bernardino, San Bernardino, CA, United States
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Brunet NM. Affective evaluation of consciously perceived emotional faces reveals a "correct attribution effect". Front Psychol 2023; 14:1146107. [PMID: 37303898 PMCID: PMC10249471 DOI: 10.3389/fpsyg.2023.1146107] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Accepted: 04/06/2023] [Indexed: 06/13/2023] Open
Abstract
The strength of the affective priming effect is influenced by various factors, including the duration of the prime. Surprisingly, short-duration primes that are around the threshold for conscious awareness typically result in stronger effects compared to long-duration primes. The misattribution effect theory suggest that subliminal primes do not provide sufficient cognitive processing time for the affective feeling to be attributed to the prime. Instead, the neutral target being evaluated is credited for the affective experience. In everyday social interactions, we shift our gaze from one face to another, typically contemplating each face for only a few seconds. It is reasonable to assume that no affective priming takes place during such interactions. To investigate whether this is indeed the case, participants were asked to rate the valence of faces displayed one by one. Each face image simultaneously served as both a target (primed by the previous trial) and a prime (for the next trial). Depending on the participant's response time, images were typically displayed for about 1-2 s. As predicted by the misattribution effect theory, neutral targets were not affected by positive affective priming. However, non-neutral targets showed a robust priming effect, with emotional faces being perceived as even more negative or positive when the previously seen face was emotionally congruent. These results suggest that a "correct attribution effect" modulates how we perceive faces, continuously impacting our social interactions. Given the importance of faces in social communication, these findings have wide-ranging implications.
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Affiliation(s)
- Nicolas M. Brunet
- Department of Psychology and Neuroscience, Millsaps College, Jackson, MS, United States
- Department of Psychology, California State University, San Bernardino, San Bernardino, CA, United States
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Grondhuis SN, Jimmy A, Teague C, Brunet NM. Having Difficulties Reading the Facial Expression of Older Individuals? Blame It on the Facial Muscles, Not the Wrinkles. Front Psychol 2021; 12:620768. [PMID: 34149508 PMCID: PMC8211723 DOI: 10.3389/fpsyg.2021.620768] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Accepted: 04/30/2021] [Indexed: 11/13/2022] Open
Abstract
Previous studies have found it is more difficult identifying an emotional expression displayed by an older than a younger face. It is unknown whether this is caused by age-related changes such as wrinkles and folds interfering with perception, or by the aging of facial muscles, potentially reducing the ability of older individuals to display an interpretable expression. To discriminate between these two possibilities, participants attempted to identify facial expressions under different conditions. To control for the variables (wrinkles/folds vs facial muscles), we used Generative Adversarial Networks to make faces look older or younger. Based upon behavior data collected from 28 individuals, our model predicts that the odds of correctly identifying the expressed emotion of a face reduced 16.2% when younger faces (condition 1) are artificially aged (condition 3). Replacing the younger faces with natural old-looking faces (Condition 2), however, results in an even stronger effect (odds of correct identification decreased by 50.9%). Counterintuitively, making old faces (Condition 2) look young (Condition 4) results in the largest negative effect (odds of correct identification decreased by 74.8% compared with natural young faces). Taken together, these results suggest that both age-related decline in the facial muscles' ability to express facial emotions and age-related physical changes in the face, explain why it is difficult to recognize facial expressions from older faces; the effect of the former, however, is much stronger than that of the latter. Facial muscle exercises, therefore, might improve the capacity to convey facial emotional expressions in the elderly.
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Affiliation(s)
- Sabrina N Grondhuis
- Department of Psychology and Neuroscience, Millsaps College, Jackson, MS, United States
| | - Angela Jimmy
- Department of Psychology and Neuroscience, Millsaps College, Jackson, MS, United States
| | - Carolina Teague
- Department of Psychology and Neuroscience, Millsaps College, Jackson, MS, United States
| | - Nicolas M Brunet
- Department of Psychology and Neuroscience, Millsaps College, Jackson, MS, United States
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Abstract
No formal studies have reported how glasses influence age perception, except for a London Vision Clinic survey that found that people over 45 look 5 or more years older when wearing eyeglasses. To investigate the effect of eyeglasses and sunglasses on age perception while controlling for age and interpersonal differences, we digitally manipulated the photographs of faces of 50 young adults, to create two age conditions (young and old) and three eyewear conditions (no glasses, eyeglasses, and sunglasses). Participants then estimated the age of the faces, displayed in random order. Contrary to the generally accepted beliefs that wearing eyeglasses makes you look older and wearing sunglasses make you look younger, our results suggest that the effect of glasses on age perception is rather small.
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Affiliation(s)
- Nicolas M. Brunet
- Department of Psychology and Neuroscience,
Millsaps
College, Jackson, Mississippi, United States
| | - Jonathan Sharp
- Department of Psychology and Neuroscience,
Millsaps
College, Jackson, Mississippi, United States
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Abstract
Many studies have reported visual cortical gamma-band activity related to stimulus processing and cognition. Most respective studies used artificial stimuli, and the few studies that used natural stimuli disagree. Electrocorticographic (ECoG) recordings from awake macaque areas V1 and V4 found gamma to be abundant during free viewing of natural images. In contrast, a study using ECoG recordings from V1 of human patients reported that many natural images induce no gamma and concluded that it is not necessary for seeing. To reconcile these apparently disparate findings, we reanalyzed those same human ECoG data recorded during presentation of natural images. We find that the strength of gamma is positively correlated with different image-computable metrics of image structure. This holds independently of the precise metric used to quantify gamma. In fact, an average of previously used gamma metrics reflects image structure most robustly. Gamma was sufficiently diagnostic of image structure to differentiate between any possible pair of images with >70% accuracy. Thus, while gamma might be weak for some natural images, the graded strength of gamma reflects the graded degree of image structure, and thereby conveys functionally relevant stimulus properties.
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Affiliation(s)
- Nicolas M Brunet
- Millsaps College, Department of Psychology and Neuroscience, 1701 North State Street, Jackson, MS, 39210, USA
| | - Pascal Fries
- Ernst Strüngmann Institute (ESI) for Neuroscience in Cooperation with Max Planck Society, Deutschordenstraße 46, 60528, Frankfurt, Germany; Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Kapittelweg 29, 6525 EN, Nijmegen, Netherlands.
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de Pesters A, Coon WG, Brunner P, Gunduz A, Ritaccio AL, Brunet NM, de Weerd P, Roberts MJ, Oostenveld R, Fries P, Schalk G. Alpha power indexes task-related networks on large and small scales: A multimodal ECoG study in humans and a non-human primate. Neuroimage 2016; 134:122-131. [PMID: 27057960 PMCID: PMC4912924 DOI: 10.1016/j.neuroimage.2016.03.074] [Citation(s) in RCA: 66] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Accepted: 03/28/2016] [Indexed: 12/19/2022] Open
Abstract
Performing different tasks, such as generating motor movements or processing sensory input, requires the recruitment of specific networks of neuronal populations. Previous studies suggested that power variations in the alpha band (8-12Hz) may implement such recruitment of task-specific populations by increasing cortical excitability in task-related areas while inhibiting population-level cortical activity in task-unrelated areas (Klimesch et al., 2007; Jensen and Mazaheri, 2010). However, the precise temporal and spatial relationships between the modulatory function implemented by alpha oscillations and population-level cortical activity remained undefined. Furthermore, while several studies suggested that alpha power indexes task-related populations across large and spatially separated cortical areas, it was largely unclear whether alpha power also differentially indexes smaller networks of task-related neuronal populations. Here we addressed these questions by investigating the temporal and spatial relationships of electrocorticographic (ECoG) power modulations in the alpha band and in the broadband gamma range (70-170Hz, indexing population-level activity) during auditory and motor tasks in five human subjects and one macaque monkey. In line with previous research, our results confirm that broadband gamma power accurately tracks task-related behavior and that alpha power decreases in task-related areas. More importantly, they demonstrate that alpha power suppression lags population-level activity in auditory areas during the auditory task, but precedes it in motor areas during the motor task. This suppression of alpha power in task-related areas was accompanied by an increase in areas not related to the task. In addition, we show for the first time that these differential modulations of alpha power could be observed not only across widely distributed systems (e.g., motor vs. auditory system), but also within the auditory system. Specifically, alpha power was suppressed in the locations within the auditory system that most robustly responded to particular sound stimuli. Altogether, our results provide experimental evidence for a mechanism that preferentially recruits task-related neuronal populations by increasing cortical excitability in task-related cortical areas and decreasing cortical excitability in task-unrelated areas. This mechanism is implemented by variations in alpha power and is common to humans and the non-human primate under study. These results contribute to an increasingly refined understanding of the mechanisms underlying the selection of the specific neuronal populations required for task execution.
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Affiliation(s)
- A de Pesters
- Nat Ctr for Adapt Neurotech, Wadsworth Center, NY State Dept of Health, Albany, NY, USA; Dept of Biomed Sci, State Univ of New York at Albany, Albany, NY, USA.
| | - W G Coon
- Nat Ctr for Adapt Neurotech, Wadsworth Center, NY State Dept of Health, Albany, NY, USA.
| | - P Brunner
- Nat Ctr for Adapt Neurotech, Wadsworth Center, NY State Dept of Health, Albany, NY, USA; Dept of Neurology, Albany Medical College, Albany, NY, USA.
| | - A Gunduz
- Dept of Biomed Eng, Univ of Florida, Gainesville, FL, USA.
| | - A L Ritaccio
- Dept of Neurology, Albany Medical College, Albany, NY, USA.
| | - N M Brunet
- SUNY Downstate Med Ctr, Brooklyn, NY, USA.
| | - P de Weerd
- Dept of Cogn Neurosci, Maastricht Univ, Maastricht, Netherlands; Donders Inst for Brain, Cognition and Behaviour, Nijmegen, Netherlands.
| | - M J Roberts
- Donders Inst for Brain, Cognition and Behaviour, Nijmegen, Netherlands.
| | - R Oostenveld
- Donders Inst for Brain, Cognition and Behaviour, Nijmegen, Netherlands.
| | - P Fries
- Donders Inst for Brain, Cognition and Behaviour, Nijmegen, Netherlands; Ernst Strüngmann Inst for Neurosci, Frankfurt, Germany.
| | - G Schalk
- Nat Ctr for Adapt Neurotech, Wadsworth Center, NY State Dept of Health, Albany, NY, USA; Dept of Biomed Sci, State Univ of New York at Albany, Albany, NY, USA; Dept of Neurology, Albany Medical College, Albany, NY, USA.
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Brunet NM, Chase PB, Mihajlović G, Schoffstall B. Ca(2+)-regulatory function of the inhibitory peptide region of cardiac troponin I is aided by the C-terminus of cardiac troponin T: Effects of familial hypertrophic cardiomyopathy mutations cTnI R145G and cTnT R278C, alone and in combination, on filament sliding. Arch Biochem Biophys 2014; 552-553:11-20. [PMID: 24418317 PMCID: PMC4043889 DOI: 10.1016/j.abb.2013.12.021] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2013] [Revised: 12/10/2013] [Accepted: 12/28/2013] [Indexed: 01/10/2023]
Abstract
Investigations of cardiomyopathy mutations in Ca(2+) regulatory proteins troponin and tropomyosin provide crucial information about cardiac disease mechanisms, and also provide insights into functional domains in the affected polypeptides. Hypertrophic cardiomyopathy-associated mutations TnI R145G, located within the inhibitory peptide (Ip) of human cardiac troponin I (hcTnI), and TnT R278C, located immediately C-terminal to the IT arm in human cardiac troponin T (hcTnT), share some remarkable features: structurally, biochemically, and pathologically. Using bioinformatics, we find compelling evidence that TnI and TnT, and more specifically the affected regions of hcTnI and hcTnT, may be related not just structurally but also evolutionarily. To test for functional interactions of these mutations on Ca(2+)-regulation, we generated and characterized Tn complexes containing either mutation alone, or both mutations simultaneously. The most important results from in vitro motility assays (varying [Ca(2+)], temperature or HMM density) show that the TnT mutant "rescued" some deleterious effects of the TnI mutant at high Ca(2+), but exacerbated the loss of function, i.e., switching off the actomyosin interaction, at low Ca(2+). Taken together, our experimental results suggest that the C-terminus of cTnT aids Ca(2+)-regulatory function of cTnI Ip within the troponin complex.
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Affiliation(s)
- Nicolas M Brunet
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
| | - P Bryant Chase
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA; Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA.
| | - Goran Mihajlović
- Department of Physics, Florida State University, Tallahassee, FL 32306, USA
| | - Brenda Schoffstall
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
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Schoffstall B, Brunet NM, Mihajlović G, Chase PB. Ca2+-Regulatory Function of the Inhibitory Peptide Region of Cardiac Troponin I is Aided by the C-Terminus of Cardiac Troponin T: Effects of FHC Mutations Ctni R145G and Ctnt R278C, Alone and in Combination, on Filament Sliding. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.4228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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Schoffstall B, LaBarbera VA, Brunet NM, Gavino BJ, Herring L, Heshmati S, Kraft BH, Inchausti V, Meyer NL, Moonoo D, Takeda AK, Chase PB. Interaction between troponin and myosin enhances contractile activity of myosin in cardiac muscle. DNA Cell Biol 2011; 30:653-9. [PMID: 21438758 DOI: 10.1089/dna.2010.1163] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Ca(2+) signaling in striated muscle cells is critically dependent upon thin filament proteins tropomyosin (Tm) and troponin (Tn) to regulate mechanical output. Using in vitro measurements of contractility, we demonstrate that even in the absence of actin and Tm, human cardiac Tn (cTn) enhances heavy meromyosin MgATPase activity by up to 2.5-fold in solution. In addition, cTn without Tm significantly increases, or superactivates sliding speed of filamentous actin (F-actin) in skeletal motility assays by at least 12%, depending upon [cTn]. cTn alone enhances skeletal heavy meromyosin's MgATPase in a concentration-dependent manner and with sub-micromolar affinity. cTn-mediated increases in myosin ATPase may be the cause of superactivation of maximum Ca(2+)-activated regulated thin filament sliding speed in motility assays relative to unregulated skeletal F-actin. To specifically relate this classical superactivation to cardiac muscle, we demonstrate the same response using motility assays where only cardiac proteins were used, where regulated cardiac thin filament sliding speeds with cardiac myosin are >50% faster than unregulated cardiac F-actin. We additionally demonstrate that the COOH-terminal mobile domain of cTnI is not required for this interaction or functional enhancement of myosin activity. Our results provide strong evidence that the interaction between cTn and myosin is responsible for enhancement of cross-bridge kinetics when myosin binds in the vicinity of Tn on thin filaments. These data imply a novel and functionally significant molecular interaction that may provide new insights into Ca(2+) activation in cardiac muscle cells.
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Butcher MT, Chase PB, Hermanson JW, Clark AN, Brunet NM, Bertram JEA. Contractile properties of muscle fibers from the deep and superficial digital flexors of horses. Am J Physiol Regul Integr Comp Physiol 2010; 299:R996-R1005. [PMID: 20702801 DOI: 10.1152/ajpregu.00510.2009] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Equine digital flexor muscles have independent tendons but a nearly identical mechanical relationship to the main joint they act upon. Yet these muscles have remarkable diversity in architecture, ranging from long, unipennate fibers ("short" compartment of DDF) to very short, multipennate fibers (SDF). To investigate the functional relevance of the form of the digital flexor muscles, fiber contractile properties were analyzed in the context of architecture differences and in vivo function during locomotion. Myosin heavy chain (MHC) isoform fiber type was studied, and in vitro motility assays were used to measure actin filament sliding velocity (V(f)). Skinned fiber contractile properties [isometric tension (P(0)/CSA), velocity of unloaded shortening (V(US)), and force-Ca(2+) relationships] at both 10 and 30°C were characterized. Contractile properties were correlated with MHC isoform and their respective V(f). The DDF contained a higher percentage of MHC-2A fibers with myosin (heavy meromyosin) and V(f) that was twofold faster than SDF. At 30°C, P(0)/CSA was higher for DDF (103.5 ± 8.75 mN/mm(2)) than SDF fibers (81.8 ± 7.71 mN/mm(2)). Similarly, V(US) (pCa 5, 30°C) was faster for DDF (2.43 ± 0.53 FL/s) than SDF fibers (1.20 ± 0.22 FL/s). Active isometric tension increased with increasing Ca(2+) concentration, with maximal Ca(2+) activation at pCa 5 at each temperature in fibers from each muscle. In general, the collective properties of DDF and SDF were consistent with fiber MHC isoform composition, muscle architecture, and the respective functional roles of the two muscles in locomotion.
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Affiliation(s)
- M T Butcher
- Dept. of Biological Sciences, Youngstown State University, OH 44555, USA.
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Moonoo D, Meyer NL, Inchausti V, Brunet NM, LaBarbera V, Chase PB, Schoffstall B. Molecular Function of the C-terminal Domain of Cardiac Troponin I. Biophys J 2010. [DOI: 10.1016/j.bpj.2009.12.1927] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
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Schoffstall B, Brunet NM, Williams S, Miller VF, Barnes AT, Wang F, Compton LA, McFadden LA, Taylor DW, Seavy M, Dhanarajan R, Chase PB. Ca2+ sensitivity of regulated cardiac thin filament sliding does not depend on myosin isoform. J Physiol 2006; 577:935-44. [PMID: 17008370 PMCID: PMC1890378 DOI: 10.1113/jphysiol.2006.120105] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Myosin heavy chain (MHC) isoforms in vertebrate striated muscles are distinguished functionally by differences in chemomechanical kinetics. These kinetic differences may influence the cross-bridge-dependent co-operativity of thin filament Ca(2+) activation. To determine whether Ca(2+) sensitivity of unloaded thin filament sliding depends upon MHC isoform kinetics, we performed in vitro motility assays with rabbit skeletal heavy meromyosin (rsHMM) or porcine cardiac myosin (pcMyosin). Regulated thin filaments were reconstituted with recombinant human cardiac troponin (rhcTn) and alpha-tropomyosin (rhcTm) expressed in Escherichia coli. All three subunits of rhcTn were coexpressed as a functional complex using a novel construct with a glutathione S-transferase (GST) affinity tag at the N-terminus of human cardiac troponin T (hcTnT) and an intervening tobacco etch virus (TEV) protease site that allows purification of rhcTn without denaturation, and removal of the GST tag without proteolysis of rhcTn subunits. Use of this highly purified rhcTn in our motility studies resulted in a clear definition of the regulated motility profile for both fast and slow MHC isoforms. Maximum sliding speed (pCa 5) of regulated thin filaments was roughly fivefold faster with rsHMM compared with pcMyosin, although speed was increased by 1.6- to 1.9-fold for regulated over unregulated actin with both MHC isoforms. The Ca(2+) sensitivity of regulated thin filament sliding speed was unaffected by MHC isoform. Our motility results suggest that the cellular changes in isoform expression that result in regulation of myosin kinetics can occur independently of changes that influence thin filament Ca(2+) sensitivity.
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Affiliation(s)
- Brenda Schoffstall
- Institute of Molecular Biophysics, Department of Biological Science, Bio Unit One, Florida State University, Tallahassee, FL 32306-4370, USA
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