Abstract-Familial hypertrophic cardiomyopathy (FHC) is an inherited autosomal dominant disease caused by mutations in sarcomeric proteins. Among these, mutations that affect myosin binding protein-C (MyBP-C), an abundant component of the thick filaments, account for 20% to 30% of all mutations linked to FHC. However, the mechanisms by which MyBP-C mutations cause disease and the function of MyBP-C are not well understood. Therefore, to assess deficits due to elimination of MyBP-C, we used gene targeting to produce a knockout mouse that lacks MyBP-C in the heart. Knockout mice were produced by deletion of exons 3 to 10 from the endogenous cardiac (c) MyBP-C gene in murine embryonic stem (ES) cells and subsequent breeding of chimeric founder mice to obtain mice heterozygous (ϩ/Ϫ) and homozygous (Ϫ/Ϫ) for the knockout allele. Wild-type (ϩ/ϩ), cMyBP-C ϩ/Ϫ , and cMyBP-C Ϫ/Ϫ mice were born in accordance with Mendelian inheritance ratios, survived into adulthood, and were fertile. Western blot analyses confirmed that cMyBP-C was absent in hearts of homozygous knockout mice. Whereas cMyBP-C ϩ/Ϫ mice were indistinguishable from wild-type littermates, cMyBP-C Ϫ/Ϫ mice exhibited significant cardiac hypertrophy. Cardiac function, assessed using 2-dimensionally guided M-mode echocardiography, showed significantly depressed indices of diastolic and systolic function only in cMyBP-C Ϫ/Ϫ mice. Ca 2ϩ sensitivity of tension, measured in single skinned myocytes, was reduced in cMyBP-C Ϫ/Ϫ but not cMyBP-C ϩ/Ϫ mice. These results establish that cMyBP-C is not essential for cardiac development but that the absence of cMyBP-C results in profound cardiac hypertrophy and impaired contractile function. Key Words: myosin binding protein-C Ⅲ heart Ⅲ myocardium Ⅲ gene knockout Ⅲ sarcomeric proteins M yosin binding protein-C (MyBP-C), also known as C-protein, 1 is a thick filament accessory protein that is present in nearly all vertebrate striated muscles but whose function is unknown. Nonetheless, there is compelling evidence to suggest that MyBP-C is a significant determinant of muscle contractile properties. In particular, cardiac MyBP-C (cMyBP-C) is a target for phosphorylation in response to various inotropic stimuli, including sympathetic stimuli that effect trisphosphorylation of cMyBP-C via cAMP-dependent protein kinase (PKA). 2 In addition, mutations of the cMyBP-C gene are a leading cause of familial hypertrophic cardiomyopathy (FHC), 3 an inherited disorder linked to mutations in cardiac contractile proteins (for review, see Bonne et al 4 and Seidman and Seidman 5 ).However, despite clues suggesting the importance of cMyBP-C to cardiac health, the function of cMyBP-C has remained enigmatic. For instance, although numerous studies have investigated effects of PKA on cardiac contractility (eg, Strang et al 6 and Patel et al 7 ), the role, if any, of cMyBP-C in mediating contractile responses to PKA has been difficult to discern. 8 -10 Similarly, the mechanisms by which cMyBP-C mutations affect cardiac function are not well understo...

The purpose of this study was to characterize the distribution of blood flow in the rat during hindlimb unweighting (HU) and post-HU standing and exercise and examine whether the previously reported (Witzmann et al., J. Appl. Physiol. 54: 1242–1248, 1983) elevation in anaerobic metabolism observed with contractile activity in the atrophied soleus muscle was caused by a reduced hindlimb blood flow. After either 15 days of HU or cage control, blood flow was measured with radioactive microspheres during unweighting, normal standing, and running on a treadmill (15 m/min). In another group of control and experimental animals, blood flow was measured during preexercise (PE) treadmill standing and treadmill running (15 m/min). Soleus muscle blood flow was not different between groups during unweighting, PE standing, and running at 15 m/min. Chronic unweighting resulted in the tendency for greater blood flow to muscles composed of predominantly fast-twitch glycolytic fibers. With exercise, blood flow to visceral organs was reduced compared with PE values in the control rats, whereas flow to visceral organs in 15-day HU animals was unaltered by exercise. These higher flows to the viscera and to muscles composed of predominantly fast-twitch glycolytic fibers suggest an apparent reduction in the ability of the sympathetic nervous system to distribute cardiac output after chronic HU. In conclusion, because 15 days of HU did not affect blood flow to the soleus during exercise, the increased dependence of the atrophied soleus on anerobic energy production during contractile activity cannot be explained by a reduced muscle blood flow.

Brachial FMD and PAT are independent predictors of CV events and all-cause mortality. Further research to evaluate the prognostic utility of PAT is necessary to compare it with FMD as a non-invasive endothelial function test in clinical practice.

Myocardial performance is likely affected by the relative expression of the two myosin heavy chain (MyHC) isoforms, namely ␣-MyHC and ␤-MyHC. The relative expression of each isoform is regulated developmentally and in pathophysiological states. Many pathophysiological states are associated with small shifts in the relative expression of each MyHC isoform, yet the functional consequence of these shifts remains unclear. The purpose of this study was to determine the functional effect of a small shift in the relative expression of ␣-MyHC. To this end, power output was measured in rat cardiac myocyte fragments that expressed Ϸ12% ␣-MyHC and in myocyte fragments that expressed Ϸ0% ␣-MyHC, as determined in the same cells by SDS-PAGE analysis after mechanical experiments. Myocyte fragments expressing Ϸ12% ␣-MyHC developed Ϸ52% greater peak normalized power output than myocyte fragments expressing Ϸ0% ␣-MyHC. These results indicate that small amounts of ␣-MyHC expression significantly augment myocyte power output. M yocardial performance demonstrates plasticity through protein isoform switches. 1 One cardiac protein, whose isoform expression influences myocardial performance, is myosin heavy chain (MyHC), the molecular motor that drives myocardial contraction. 2 Two functionally diverse MyHC isoforms are expressed in mammalian myocardium, ␣-MyHC and ␤-MyHC. The two MyHC isoforms display 93% amino acid identity, 3 yet ␣-MyHC exhibits two to three times faster actin-activated ATPase activity 4 and actin filament sliding velocity. 5 Similarly, myocyte fragments that express exclusively ␣-MyHC generate nearly three times greater peak normalized power than myocytes expressing only ␤-MyHC. 6 The relative expression of each MyHC isoform varies throughout mammalian development 7 and in pathophysiological conditions such as hypothyroidism, 7 diabetes, 8 hypertension, 4 and heart failure. 9,10 In rodents, pathophysiological conditions are associated with the downregulation of ␣-MyHC and the concomitant upregulation of ␤-MyHC expression. 4,7,8 Interestingly, recent evidence has demonstrated a similar downregulation of ␣-MyHC protein expression and upregulation of ␤-MyHC expression in failing human hearts. 9,10 These studies have shown that normal adult human hearts express a small but detectable amount of ␣-MyHC protein, whereas failing human hearts express exclusively ␤-MyHC. The functional consequence of such a small shift in MyHC isoform expression, however, is unclear. Therefore, the purpose of this study was to determine if a small amount of ␣-MyHC protein expression is sufficient to augment single cardiac myocyte function. To this end, power output was measured in single myocyte fragments that expressed small amounts of ␣-MyHC and in fragments that expressed Ϸ0% ␣-MyHC (ie, 100% ␤-MyHC). The relative expression of ␣-MyHC and ␤-MyHC was determined for each myocyte by SDS-PAGE analysis and silver staining after mechanical measurements, thereby providing a direct correlation between relative MyHC isoform expression and myocyte ...