Cardiac myocyte membrane wounding in the abruptly pressure-overloaded rat heart under high wall stress.

The potential role of transient sarcolemmal membrane wounding as a signal transduction event for cardiomyocyte hypertrophy was evaluated in rats with short-term pressure overload caused by banding of the proximal aorta. This procedure resulted in significant increases in left ventricular systolic (1.5-fold) and end-diastolic (2.6-fold) pressures and wall stresses that were associated with significant wall thinning and cavitary enlargement. Quantitative image analysis of frozen sections of the stressed ventricles obtained 60 minutes after banding demonstrated a 6- to 10-fold increase in cytosolic staining with a horseradish peroxidase-labeled anti-albumin antibody compared with sham-operated controls, indicating that an increase in transient sarcolemmal membrane permeability (wounding) is an early response to an abrupt increase in hemodynamic load in vivo. We conclude that an intense hemodynamic stress in vivo can result in histologically detectable cardiomyocyte wounding.

Loss of cytoplasmic basic fibroblast growth factor from physiologically wounded myofibers of normal and dystrophic muscle.

Using muscle as an in vivo model system, we have tested the hypothesis that basic fibroblast growth factor is released from a cytoplasmic storage site into the extra-cellular environment via diffusion through survivable, mechanically-induced plasma membrane disruptions. Normal and dystrophic (mdx) mouse muscle were studied. Strong immunostaining for bFGF was detected in the cytoplasm of myofibers of uninjured muscle fixed in situ by perfusion. By contrast, myofibers did not stain cytoplasmically for bFGF after suffering lethal disruptions of their plasma membranes caused by freezing and thawing followed by sectioning. Sub-lethal, transient disruptions of myofiber plasma membranes--termed plasma membrane 'wounds'--were shown to be induced by needle puncture or exercise of muscle. Quantitative image analysis revealed that these wounded fibers contained significantly reduced levels of bFGF. Dystrophic exercised and unexercised muscle was found to possess an approximately 6-fold higher proportion of wounded myofibers than does normal muscle under equivalent conditions. Release of bFGF at a rate that is a direct function of the frequency of myofiber wounding may explain in part how a muscle adjusts its growth to meet changing mechanical demand as well as the pathological hypertrophy characteristic of certain stages of muscular dystrophy.

Restitution of frog gastric mucosa in vitro: effect of basic fibroblast growth factor.

BACKGROUND: Rapid re-epithelialization after superficial gastric mucosal injury is caused by migration of persisting viable epithelial cells. Basic fibroblast growth factor (bFGF) has been reported to enhance the healing of experimental duodenal ulcer, but its mode of action is unclear. The present experiments examine whether an effect of bFGF on restitution might contribute to such healing. METHODS: Paired halves of bullfrog fundic gastric mucosa in Ussing chambers were injured by luminal exposure to 1 mol/L NaCl for 10 minutes. RESULTS: Luminal protamine or suramin, both known to interfere with endogenous bFGF, significantly inhibited electrophysiological recovery at neutral luminal pH (pHL). Luminal sucrose octasulfate, which prevents acid degradation of bFGF, and an exogenous, acid-resistant form of bFGF allowed electrophysiological recovery at a pHL of 3.0 that completely prevented restitution in control tissues. Electrophysiological recovery correlated well with morphological restitution. The presence of endogenous bFGF in normal and restituting bullfrog mucosa was confirmed by positive staining with a monoclonal antibody. CONCLUSIONS: It is concluded that rapid epithelial repair after surface injury is at least in part mediated by bFGF.

Disruptions of muscle fiber plasma membranes. Role in exercise-induced damage.

The authors have tested the hypothesis that plasma membrane disruptions are an early form of structural damage to the fibers of eccentrically exercised muscle. Rat serum albumin (RSA) was used as a marker for muscle-fiber wounding in the rat tricep (medial head) exercised eccentrically by downhill running. In all muscles examined, strong staining with a horseradish peroxidase (HRP)-conjugated anti-RSA antibody was observed between fibers (intercellular staining) and also within certain fibers (intracellular staining). This intracellular staining was interpreted as identifying muscle fibers wounded at their plasma membranes and hence rendered transiently or permanently permeable to extracellular RSA. The most striking finding of this study was a 6.9-fold increase relative to unexercised controls in the number of wounded cells in the medial head immediately after eccentric exercise. The authors also reproducibly observed, albeit less frequently, myocytes that stained with anti-RSA in the medial head and several other muscles of the "unexercised," caged laboratory rat. The extreme vulnerability of muscle plasma membranes to mechanically induced stress was revealed in this study by HRP injections into the triceps long head. A single injection of 200 microliters HRP through a 26-gauge needle resulted in extensive labeling of the muscle fibers present in the long head cross-sectioned at the injection site. The authors propose that initially resealable and/or highly localized, unsealable membrane wounds are an early form of exercise-induced damage that could progress along the length of the fiber until, 1 to 4 days after eccentric exercise, it becomes sufficiently severe that it can be readily recognized as the frank fiber necrosis and cellular infiltration described in numerous previous studies. In possessing cells wounded at their plasma membranes, normal, undisturbed rat muscle and eccentrically exercised muscle appears to resemble gut and skin, two additional tissues routinely exposed to mechanical forces in vivo. The authors propose that membrane disruptions provide a route into and out of myofiber cytoplasm distinct from the conventional, membrane-bounded routes of endo- and exocytosis, and therefore may be of importance both technically, as a route for introducing foreign genes into muscle cells, and biologically, as a route for release of the growth factor, basic fibroblast growth factor.