Abstract: Objective To test whether stimulation of integrins on neonatal rat cardiomyocytes (NRCMs) would favor uptake of macromolecules. Methods NRCMs were treated with Gly-Arg-Gly-Asp-Ser (RGD, 100-300 mg/L) to stimulate integrins, or phosphate-buffered saline, in the presence of ovalbumin-texas red (OTR, 45 kD) or dextran-texas red (DTR, 70 kD). After 8 hours, 16 hours, 24 hours, uptake of red label as well as Dysferlin immunoreactivity were quantified by fluorescence microscopy. Results Uptake of OTR and DTR by NRCMs was intensified by RGD ( for trend EM>P/EM><0.001 and EM>P/EM><0.05, respectively) and was correlated with duration of incubation (EM>P/EM><0.001 for both). RGDinduced uptake of OTR by NRCMs was correlated with OTR concentration (EM>P/EM><0.001). The Dysferlin-positive areas in RGD-treated NRCMs were about 3-fold larger than in NRCMs incubated without RGD (EM>P/EM><0.001). However, in non-beating NRCMs RGD did not induce larger dysferlin-positive areas, nor did RGD stimulate uptake of OTR. Conclusion In NRCMs stimulation of integrins caused uptake of labeled macromolecules. Dysferlin may be involved in membrane repair following RGD-induced membrane wounding. RGD-induced membrane wounding is closely associated with contractile behavior of the NRCMs.

Key words: Cardiomyocyte, Integrin, Dysferlin, Membrane wounding, RGD, Immunofluorescence, Rat 