Increased myosin orientation during muscle contraction: a measure of cardiac contractility

Development of abnormal tissue architecture in transplanted neonatal rat myocytes

BACKGROUND

Most myocardial cell transplant studies focus on demonstration of improved function; however, such improvement depends on the development of appropriate tissue structure. Thus, our aim was to assess the architectural changes that occurred after cell transplant into normal and infarcted myocardium.

METHODS

Male neonatal cells (1 to 2 days old) were injected into the left ventricular free wall of adult female rats. The tissue was examined 0 to 1 days and 1 to 2, 4 to 6, and 12 weeks later in noninfarcted hearts and 6 months after transplant into infarcts. In histologic sections, we assessed the cells' retardation of polarized light (to measure development of contractile elements), two-dimensional cell orientation, cell nuclear morphology, and collagen content.

RESULTS

The transplant cells' retardation of polarized light gradually increased to 81% of that of host cells after 6 months (p < 0.001). The transplant cells were disorganized and although their nuclei increased in size, they always had a rounded appearance. Collagen content in the transplant was 210% to 430% higher than in host tissue (p < 0.01). In addition, scar collagen always separated transplant and host cells.

CONCLUSIONS

One architectural feature, the rounded nuclei, provided a distinctive marker to identify transplanted cells. Nevertheless, the transplants' inhibited muscle development together with disorganization, separation from the host muscle, and a substantial increase in collagen resulted in a structure unlikely to play an active role in systolic function.

The natural substrate for nitric oxide synthase activity

There has been little evidence to indicate that arginine is the natural substrate for generating nitric oxide synthase (NOS) activity. It is now shown that carnosine, which is widely distributed in tissues, is likely to be the true substrate. In tissue sections it gives a stronger NOS reaction than does arginine.

Histologic signatures of thermal injury: applications in transmyocardial laser revascularization and radiofrequency ablation

BACKGROUND AND OBJECTIVE

Cardiac treatments such as transmyocardial laser revascularization and radiofrequency ablation cause thermal injury. We sought to provide quantitative histologic methods of assessing such injury by using the inherent birefringence of cardiac muscle and collagen; specifically, to exploit the connection between thermal injury and the loss of birefringence.

STUDY DESIGN/MATERIALS AND METHODS

We quantified tissue birefringence changes in vitro for temperatures up to 130 degrees C. This information was used to assess thermal injury associated with myocardial channels made in vitro. We then measured in vivo cardiac injury 30 minutes and 3 days after radiofrequency exposure.

RESULTS

Birefringence decreased above 60 degrees C for muscle and above 70 degrees C for collagen. Temperatures above 80 degrees C were associated with collagen fiber straightening and above 95 degrees C with little muscle birefringence. Injury adjacent to laser channels was greatest parallel to cell orientation. In vivo, muscle with reduced birefringence was surrounded by cells exhibiting focal birefringence increases (contraction bands). Early injury assessment marked by birefringence changes corresponded to lesion size at 3 days.

CONCLUSION

Polarized light revealed histologic temperature signatures corresponding to irreversible muscle injury and collagen denaturation.

St. Thomas' Hospital cardioplegia: enhanced protection with exogenous creatine phosphate

BACKGROUND

Experimentally, creatine phosphate (CP) improves postischemic recovery of function and reduces postischemic arrhythmias.

METHODS

We studied 50 patients undergoing valve replacement. They were randomized into either a control group, who received St. Thomas' Hospital cardioplegic solution No. 1, or a CP-treated group, receiving the same cardioplegic solution plus CP (10 mmol/L). There were no preoperative clinical differences between groups. Assessment was by electrocardiographic analysis, inotropic drug requirement, quantitative birefringence, myocardial high-energy phosphate content, function, and semiquantitative ultrastructural assessment.

RESULTS

Direct-current shocks were reduced in the CP-treated group (0.88 +/- 0.15) compared with the control group (1.40 +/- 0.14; p < 0.02), as was the total number of joules (22.0 +/- 3.5 versus 34.4 +/- 3.7, respectively; p <0.02). The incidence of spontaneous sinus rhythm was higher in the CP-treated group (40% versus 8%; p < 0.05) and the incidence of postoperative arrhythmias, lower (8% versus 32%; p < 0.05). Prolonged inotropic administration (12 hours or longer) occurred in fewer patients in the CP-treated group (4% versus 28%; p < 0.05). Response to inotropic support (in the subset of patients requiring this treatment) was significantly greater in the CP-treated group than in the control group. There were no differences in recovery of function, birefringence changes, myocardial high-energy phosphate content, or ultrastructure between groups.

CONCLUSIONS

St. Thomas' Hospital cardioplegic solution No. 1 plus CP enhanced myocardial protection and conferred a direct benefit to the patient by reducing postoperative arrhythmias and need of prolonged inotropic support.