The source of epifluorescence in isolated perfused heart loaded with fura 2-AM or indo 1-AM.

The purpose of this study is to clarify the kinds of cells that fluoresce in isolated perfused heart intracoronarily loaded with fura 2-AM or indo 1-AM. The hearts from hamsters perfused by the Langendorff method were loaded with fura 2-AM or indo 1-AM intracoronarily. The epicardium was excited by ultraviolet light at a wavelength of 340 or 380 nm (fura 2) or 360 nm (indo 1). Epifluorescent images from arrested hearts prepared with St Thomas' cardioplegic solution were observed through an inverted microscope and taken by a still camera. Endothelial cells and pericytes of the capillaries showed intense fluorescence. In the intercapillary spaces, a less intense but still apparent fluorescence emitted by myocytes could also be detected. On the other hand, fluorescence from smooth muscle cells and fibroblasts could not be identified. Therefore, epifluorescence in the isolated perfused heart loaded with fura 2-AM or indo 1-AM was mainly generated within endothelial cells, pericytes, and myocytes. To evaluate calcium fluorescence in isolated hearts quantitatively, the fluorescence of endothelial cells and pericytes of the capillaries must be taken into consideration.