We evaluated the ability of M-mode and Doppler echocardiography to assess left ventricular (LV) function reliably and repeatedly in mice and tested whether these techniques could detect physiological alterations in phospholamban (PLB)-deficient mice. Anesthetized wild-type mice (n = 7) and mice deficient in PLB (n = 8) were studied with two-dimensional guided M-mode and Doppler echocardiography using a 9-MHz imaging and 5- to 7.5-MHz Doppler transducer. Data were acquired in the baseline state and after intraperitoneal isoproterenol administration (2.0 micrograms/g IP). Interobserver and intraobserver variability and reproducibility were excellent. PLB-deficient mice were associated with significant (P < .05) increases in several physiological parameters (mean +/- SD) compared with wild-type control mice: normalized mean velocity of circumferential shortening (7.7 +/- 2.1 versus 5.5 +/- 1.0 circ/sec), peak aortic velocity (105 +/- 13 versus 75 +/- 9.2 cm/s), mean aortic acceleration (57 +/- 16 versus 31 +/- 4 m/s2), and peak early-diastolic transmitral velocity (80.0 +/- 7.2 versus 66.9 +/- 7.7 cm/s). LV dimensions, shortening fractions, heart rates, late diastolic transmitral (A) velocities, and early to late (E/A) diastolic velocity ratios were similar in both groups. Isoproterenol administration resulted in significant increases in Doppler indices of ventricular function in control but not PLB-deficient mice. These findings indicate that assessment of LV function can be performed noninvasively in mice under varying physiological conditions and that PLB regulates basal LV function in vivo.

Currently at least 11 protein kinase C (PKC) isoforms have been identified and may play different roles in cell signaling pathways leading to changes in cardiac contractility, the hypertrophic response, and tolerance to myocardial ischemia. The purpose of the present study was to test the hypothesis that responses of individual PKC isoforms to distinct pathological stimuli were differentially regulated in the adult guinea pig heart. Isolated hearts were perfused by the Langendorff method and were exposed to ischemia, hypoxia, H(2)O(2), or angiotensin II. Hypoxia and ischemia induced translocation of PKC isoforms alpha, beta(2), gamma, and zeta, and H(2)O(2) translocated PKC isoforms alpha, beta(2), and zeta. Angiotensin II produced translocation of alpha, beta(2), epsilon, gamma, and zeta isoforms. Inhibition of phospholipase C with tricyclodecan-9-yl-xanthogenate (D609) blocked hypoxia-induced (alpha, beta(2), and zeta) and angiotensin II-induced (alpha, beta(2), gamma, and zeta) translocation of PKC isoforms. Inhibition of tyrosine kinase with genistein blocked translocation of PKC isoforms by hypoxia (beta(2) and zeta) and by angiotensin II (beta(2)). By contrast, neither D609 nor genistein blocked H(2)O(2)-induced translocation of any PKC isoform. We conclude that hypoxia-induced activation of PKC isoforms is mediated through pathways involving phospholipase C and tyrosine kinase, but oxidative stress may activate PKC isoforms independently of Galphaq-phospholipase C coupling and tyrosine kinase signaling. Because oxidative stress may directly activate PKC, and PKC activation appears to be involved in human heart failure, selective inhibition of the PKC isoforms may provide a novel therapeutic strategy for the prevention and treatment of this pathological process.

Ventricular arrhythmias are common in both cardiac hypertrophy and failure; cardiac failure in particular is associated with a significant increase in the risk of sudden cardiac death. We studied the electrophysiologic changes in a guinea pig model with aortic banding resulting in cardiac hypertrophy at 4 weeks and progressing to cardiac failure at 8 weeks using whole-cell patch-clamp and biochemical techniques. Action potential durations (APDs) were significantly prolonged in banded animals at 4 and 8 weeks compared with age-matched sham-operated animals. APDs at 50% and 90% repolarization (APD(50) and APD(90) in ms) were the following: 4 week, banded, 208+/-51 and 248+/-49 (n = 15); 4 week, sham, 189+/-68 and 213+/-69 (n = 16); 8 week, banded, 197+/-40 and 226+/-40 (n = 21); and 8 week, sham, 156+/-42 and 189+/-45 (n = 22), respectively; P<0.05 comparing banded versus sham-operated animals. We observed no significant differences in the K(+) currents between the 2 groups of animals at 4 and 8 weeks. However, banded animals exhibited a significant increase in Na(+) and Na(+)-Ca(2+) exchange current densities compared with controls. Furthermore, we have found a significant attenuation in the Ca(2+)-dependent inactivation of the L-type Ca(2+) current in the banded compared with sham-operated animals, likely as a result of the significant downregulation of the sarcoplasmic reticulum Ca(2+) ATPase, which has been documented previously in the heart failure animals. Our data provide an alternate mechanism for APD prolongation in cardiac hypertrophy and failure and support the notion that there is close interaction between Ca(2+) handling and action potential profile.