Role of transiently altered sarcolemmal membrane permeability and basic fibroblast growth factor release in the hypertrophic response of adult rat ventricular myocytes to increased mechanical activity in vitro.

Abstract

One of the trophic factors that has been implicated in initiating or facilitating growth in response to increased mechanical stress in several tissues and cell types is basic fibroblast growth factor (bFGF; FGF-2). Although mammalian cardiac muscle cells express bFGF, it is not known whether it plays a role in mediating cardiac adaptation to increased load, nor how release of the cytosolic 18-kD isoform of bFGF would be regulated in response to increased mechanical stress. To test the hypothesis that increased mechanical activity induces transient alterations in sarcolemmal permeability that allow cytosolic bFGF to be released and subsequently to act as an autocrine and paracrine growth stimulus, we examined primary isolates of adult rat ventricular myocytes maintained in serum-free, defined medium that were continually paced at 3 Hz for up to 5 d. Paced myocytes, but not nonpaced control cells, exhibited a "hypertrophic" response, which was characterized by increases in the rate of phenylalanine incorporation, total cellular protein content, and cell size. These changes could be mimicked in control cells by exogenous recombinant bFGF and could be blocked in continually paced cells by a specific neutralizing anti-bFGF antibody. In addition, medium conditioned by continually paced myocytes contained significantly more bFGF measured by ELISA and more mitogenic activity for 3T3 cells, activity that could be reduced by a neutralizing anti-bFGF antibody. The hypothesis that transient membrane disruptions sufficient to allow release of cytosolic bFGF occur in paced myocytes was examined by monitoring the rate of uptake into myocytes from the medium of 10-kD dextran linked to fluorescein. Paced myocytes exhibited a significantly higher rate of fluoresceinlabeled dextran uptake. These data are consistent with the hypothesis that nonlethal, transient alterations in sarcolemmal membrane permeability with release of cytosolic bFGF is one mechanism by which increased mechanical activity could lead to a hypertrophic response in cardiac myocytes.( J. Clin. Invest. 1996. 97:281-291.)

Electrical stimulation of neonatal cardiomyocytes results in the sequential activation of nuclear genes governing mitochondrial proliferation and differentiation

“…Induction of hypertrophy in neonatal cardiac myocytes using a variety of model systems and hypertrophic stimuli is associ- (25)(26)(27)(28). Contractile stimulation of cardiac myocytes in serum-free culture results in cardiac growth and increased myofibrillar organization in vitro, suggesting that the alterations in myofibrillar content may occur by an autocrine pathway (29,30).…”

“…The mechanism by which increases in the contraction rate-e.g., by long-term electrical stimulationinfluences the process of cardiac growth and differentiation is an intense area of investigation. McDonough et al (6) have suggested that regulation of atrial natriuretic factor secretion by electrically stimulated neonatal rat cardiac myocytes is primarily dependent on contractile calcium transients and calmodulin kinase, independent of protein kinase C. Release of basic fibroblast growth factor from paced myocytes into the medium has been proposed to account for the hypertrophic response in adult rat ventricular myocytes (26). Other investigators have demonstrated that mechanical stretch activates phosphorylation cascades, including protein kinase C, mitogen-activated protein kinases and p90rsk (27).…”

Increased c-fos mRNA Expression By Human Fibroblasts Contracting Stressed Collagen Matrices

“…Significantly, mechanostimulated changes in gene expression and other cell functions often depend on autocrine signaling mechanisms (21,36,50,54,66), and cell wounding can lead to release of molecules that mediate these responses (7,9,33,42). Whether the increase in c-fos mRNA levels in response to contraction of stressed collagen matrices also depends on an autocrine mechanism remains to be studied.…”

The ulcer healing effect of protamine sulphate in rat stomach

“…The gastric mucosal bFGF levels were quanti®ed by an enzyme-linked immunosorbent assay (ELISA) measurement 18 with a bFGF ELISA kit (Wako Pure Chemical Industries Ltd, Osaka, Japan) according to the manufacturer's instructions. The mucosal samples (100 mg) were homogenized in 1 mL PBS (pH 7.4) for 30 s under ice-cold conditions, followed by centrifugation at 20 000´g for 20 min at 4°C.…”