We conclude that the VPR tail-cuff method provides accurate blood pressure measurements over the physiological range of blood pressure in mice.

The myofilament protein troponin I (TnI) has a key isoform-dependent role in the development of contractile failure during acidosis and ischemia. Here we show that cardiac performance in vitro and in vivo is enhanced when a single histidine residue present in the fetal cardiac TnI isoform is substituted into the adult cardiac TnI isoform at codon 164. The most marked effects are observed under the acute challenges of acidosis, hypoxia, ischemia and ischemia-reperfusion, in chronic heart failure in transgenic mice and in myocytes from failing human hearts. In the isolated heart, histidine-modified TnI improves systolic and diastolic function and mitigates reperfusion-associated ventricular arrhythmias. Cardiac performance is markedly enhanced in transgenic hearts during reperfusion despite a high-energy phosphate content similar to that in nontransgenic hearts, providing evidence for greater energetic economy. This pH-sensitive 'histidine button' engineered in TnI produces a titratable molecular switch that 'senses' changes in the intracellular milieu of the cardiac myocyte and responds by preferentially augmenting acute and long-term function under pathophysiological conditions. Myofilament-based inotropy may represent a therapeutic avenue to improve myocardial performance in the ischemic and failing heart.

We rescued the embryonic lethality of global PPARγ knockout by breeding Mox2-Cre (MORE) mice with floxed PPARγ mice to inactivate PPARγ in the embryo but not in trophoblasts and created a generalized PPARγ knockout mouse model, MORE-PPARγ knockout (MORE-PGKO) mice. PPARγ inactivation caused severe lipodystrophy and insulin resistance; surprisingly, it also caused hypotension. Paradoxically, PPARγ agonists had the same effect. We showed that another mouse model of lipodystrophy was hypertensive, ruling out the lipodystrophy as a cause. Further, high salt loading did not correct the hypotension in MORE-PGKO mice. In vitro studies showed that the vasculature from MORE-PGKO mice was more sensitive to endothelial-dependent relaxation caused by muscarinic stimulation, but was not associated with changes in eNOS expression or phosphorylation. In addition, vascular smooth muscle had impaired contraction in response to α-adrenergic agents. The renin-angiotensin-aldosterone system was mildly activated, consistent with increased vascular capacitance or decreased volume. These effects are likely mechanisms contributing to the hypotension. Our results demonstrated that PPARγ is required to maintain normal adiposity and insulin sensitivity in adult mice. Surprisingly, genetic loss of PPARγ function, like activation by agonists, lowered blood pressure, likely through a mechanism involving increased vascular relaxation.

Radiotelemetry of mouse blood pressure accurately monitors systolic pressure, diastolic pressure, heart rate, and locomotor activity but requires surgical implantation. Noninvasive measurements of indirect systolic blood pressure have long been available for larger rodents and now are being reported more frequently for mice. This study compared mouse systolic arterial blood pressure measurements using implanted radiotelemetry pressure transducer with simultaneous tail-cuff measurements in the same unanesthetized mice. The pressure range for comparison was extended by inducing experimental hypertension or by observations of circadian elevations between 3 AM and 6 AM. Both trained and untrained tail-cuff operators used both instruments. Every effort was made to follow recommended manufacturer's instructions. With the initial flow-based tail-cuff instrument, we made 671 comparisons (89 sessions) and found the slope of the linear regression to be 0.118, suggesting poor agreement. In an independent assessment, 277 comparisons (35 sessions) of radiotelemetry measurements with the pulse based tail-cuff instrument were made. The slope of the linear regression of the simultaneous measurements of systolic pressures was 0.98, suggesting agreement. Bland-Altman analysis also supported our interpretation of the linear regression. Thus although reliable systolic pressure measurements are possible with either tail-cuff or radiotelemetry techniques, in our hands some tail-cuff instruments fail to accurately detect elevated blood pressures. These data, however, do not distinguish whether this instrument-specific tail-cuff failure was due to operator or instrument inadequacies. We strongly advise investigators to obtain an independent and simultaneous validation of tail-cuff determinations of mouse blood pressure before making critical genotyping determinations.

Signal transduction via guanine nucleotide binding proteins (G proteins) is involved in cardiovascular, neural, endocrine, and immune cell function. Regulators of G protein signaling (RGS proteins) speed the turn-off of G protein signals and inhibit signal transduction, but the in vivo roles of RGS proteins remain poorly defined. To overcome the redundancy of RGS functions and reveal the total contribution of RGS regulation at the G␣ i2 subunit, we prepared a genomic knock-in of the RGS-insensitive G184S Gnai2 allele. The G␣ i2 G184S knock-in mice show a dramatic and complex phenotype affecting multiple organ systems (heart, myeloid, skeletal, and central nervous system). Both homozygotes and heterozygotes demonstrate reduced viability and decreased body weight. Other phenotypes include shortened long bones, a markedly enlarged spleen, elevated neutrophil counts, an enlarged heart, and behavioral hyperactivity. Heterozygous G␣ i2 ؉/G184S mice show some but not all of these abnormalities. Thus, loss of RGS actions at G␣ i2 produces a dramatic and pleiotropic phenotype which is more evident than the phenotype seen for individual RGS protein knockouts.Cell-cell communication is fundamental to the maintenance of homeostasis. The G protein-coupled receptor superfamily is arguably the most abundant and diverse protein family in cellular signaling and is tightly regulated. A novel family of Ͼ20 proteins termed regulators of G protein signaling, or RGS proteins, both tonically inhibit G protein function and also serve as signal control points (2,22,34,39,69). RGS-mediated inhibition of G protein signaling occurs through direct binding of the RGS protein to the G␣ subunit, with subsequent GTPase-accelerating protein (GAP) actions to rapidly deactivate G␣ (2). Deactivation may be accelerated up to 1,000-fold and shuts down both G␣ and G␤␥ signals (42, 48). RGS proteins may also competitively inhibit G␣ binding to effectors such as phospholipase C (32). Most of the currently known RGS proteins interact with either Gi or Gq family G proteins and influence cyclic AMP (cAMP), Ca 2ϩ , mitogen-activated protein kinase, and ion channel signaling. There is strong evidence implicating them in the subsecond kinetics of G i -and G o -mediated ion channel activation and deactivation in the heart (10, 21, 36) and neurons (36). In addition, the conserved RGS domain has been found to serve as a multifunctional protein adapter which can recruit many effectors or regulators to the vicinity of activated G proteins (31,53,62). Notable examples include p115rhoGEF (30, 40) and GRK2 (44). There is also emerging interest in RGS proteins as drug targets (9,20,53,72).However, the physiological functions of RGS proteins remain poorly defined. A number of RGS knockouts have been reported (for example, RGS1, -2, -4, and -9). The RGS9-1 knockout shows prolonged visual potentials (7), and RGS9-2 disruption results in markedly enhanced responses to drugs of abuse, such as cocaine, amphetamines, and opiates (56, 71). A human disorder, bradyopsia, with r...