Close relation of arterial ICC-like cells to the contractile phenotype of vascular smooth muscle cell

This work aimed to establish the lineage of cells similar to the interstitial cells of Cajal (ICC), the arterial ICC-like (AIL) cells, which have recently been described in resistance arteries, and to study their location in the artery wall. Segments of guinea-pig mesenteric arteries and single AIL cells freshly isolated from them were used. Confocal imaging of immunostained cells or segments and electron microscopy of artery segments were used to test for the presence and cellular localization of selected markers, and to localize AIL cells in intact artery segments. AIL cells were negative for PGP9.5, a neural marker, and for von Willebrand factor (vWF), an endothelial cell marker. They were positive for smooth muscle α-actin and smooth muscle myosin heavy chain (SM-MHC), but expressed only a small amount of smoothelin, a marker of contractile smooth muscle cells (SMC), and of myosin light chain kinase (MLCK), a critical enzyme in the regulation of smooth muscle contraction. Cell isolation in the presence of latrunculin B, an actin polymerization inhibitor, did not cause the disappearance of AIL cells from cell suspension. The fluorescence of basal lamina protein collagen IV was comparable between the AIL cells and the vascular SMCs and the fluorescence of laminin was higher in AIL cells compared to vascular SMCs. Moreover, cells with thin processes were found in the tunica media of small resistance arteries using transmis-sion electron microscopy. The results suggest that AIL cells are immature or phenotypically modulated vascular SMCs constitutively present in resistance arteries

Resident phenotypically modulated vascular smooth muscle cells in healthy human arteries.

Vascular interstitial cells (VICs) are non-contractile cells with filopodia previously described in healthy blood vessels of rodents and their function remains unknown. The objective of this study was to identify VICs in human arteries and to ascertain their role. VICs were identified in the wall of human gastro-omental arteries using transmission electron microscopy. Isolated VICs showed ability to form new and elongate existing filopodia and actively change body shape. Most importantly sprouting VICs were also observed in cell dispersal. RT-PCR performed on separately collected contractile vascular smooth muscle cells (VSMCs) and VICs showed that both cell types expressed the gene for smooth muscle myosin heavy chain (SM-MHC). Immunofluorescent labelling showed that both VSMCs and VICs had similar fluorescence for SM-MHC and αSM-actin, VICs, however, had significantly lower fluorescence for smoothelin, myosin light chain kinase, h-calponin and SM22α. It was also found that VICs do not have cytoskeleton as rigid as in contractile VSMCs. VICs express number of VSMC-specific proteins and display features of phenotypically modulated VSMCs with increased migratory abilities. VICs, therefore represent resident phenotypically modulated VSMCs that are present in human arteries under normal physiological conditions

Theory and applications of geometric scaling of localized calcium release events

Geometric measures of localized calcium release (LCR) events have been used to understand their biophysical basis. We found power law scaling between three such metrics—maximum amplitude (MA), mass above half-maximum amplitude (MHM), and area at half-maximum amplitude (AHM). In an effort to understand this scaling a minimal analytic model was employed to simulate LCR events recorded by confocal line scan. The distribution of logMHM as a function of logAHM, pMHM(pAHM), was dependent on model parameters such as channel open time, current size, line scan offset, and apparent diffusion coefficient. The distribution of log[MHM/AHM] as a function of logMA, p[MHM/AHM](pMA), was invariant, reflecting the gross geometry of the LCR event. The findings of the model were applied to real LCR line scan data from rabbit portal vein myocytes, rat cerebral artery myocytes, and guinea pig fundus knurled cells. pMHM(pAHM) could be used to distinguish two populations of LCR events in portal vein, even at the scale of “calcium noise,” and to calculate the relative current of the two. The relative current was 2. pMHM(pAHM) could also be used to study pharmacological effects. The pMHM(pAHM) distribution of knurled cell LCR events was markedly contracted by ryanodine, suggesting a reduction in channel open time. The p[MHM/AHM](pMA) distributions were invariant across all cell types and were consistent with the model, underlying the common physical basis of their geometry. The geometric scaling of LCR events demonstrated here may help with their mechanistic characterization