CHARACTERIZATION OF 2 POPULATIONS OF ECTOPIC CELLS ISOLATED FROM THE HEARTS OF NGF TRANSGENIC MICE

We have observed sympathetic hyperinnervation and hyperplasia of an un known cell population within the base of the hearts from transgenic mi ce in which nerve growth factor (NGF) expression was targeted to cardi ac tissue (Hassankhani et al., 1993, 1995). To characterize this ectop ic cell population, cells from the base of hearts of 3- to 4-week-old transgenic mice were dissociated and established in tissue culture, an d their properties were analyzed using morphological, immunocytochemic al, and physiological techniques. Morphological studies of the ectopic cells revealed the temporal expression of two different cellular phen otypes: (i) a spindle-shaped cell type, present by 1 to 2 days in, vit ro (DIV) and (ii) cells with a fiber-like morphology, detected by 7 DI V. In contrast to transgenic cardiac myocytes that express immunoreact ivity to antibodies against sarcomeric myosin, beat spontaneously (sim ilar to 60/min), and are electrically excitable, the ectopic cell type s did not stain with an antibody against sarcomeric myosin, never show ed contractile activity, and did not manifest membrane excitability. M oreover, these two types of ectopic cells demonstrated other distincti ve characteristics. The spindle-shaped subpopulation typically formed small clusters of cells that were immunostained by antibodies to GFAP, vimentin, and low-affinity NGF receptor (LNGFR) and demonstrated a lo w incidence of dye coupling (30%), whereas the fiber-like cells aligne d themselves along their long axes, immunostained for gp140(trkA), LNG FR, and anti a-smooth muscle actin and showed extensive (100%) and dif fuse dye spread to numerous other contiguous fiber-like cells. Dye spr ead was not observed between the adjacent fiber-like and the spindle-s haped cells and was reversibly blocked between homologous cells after treatment with halothane, a gap junction channel blocking agent. In co mparison to cardiac myocytes, macroscopic junctional conductance of th e spindle-shaped cells was more voltage-sensitive. At the single chann el level, unitary junctional conductances of approximately 60 pS were predominant. Overall, these results indicate that these ectopic cells are likely derived from neural crest. The spindle-shaped cells appear to be immature Schwann cells, whereas the fiber-like cells may be rela ted to the ectomesenchymal cells contributing to the morphogenesis of the cardiac outflow tract. (C) 1995 Academic Press,Inc.