The organisation of vascular smooth muscle cells; a quantitative Fast Fourier Transform (FFT) based assessment

Abstract

BackgroundThe existence of a helical arrangement of vascular smooth muscle cells in the wall of relatively large blood vessels has been known of for at least 80 years. In that time various workers have proposed mathematical models of vascular function that have incorporated one or more helix. However, most of this work has focussed on large conduit vessels such as aorta and carotid arteries. The smaller resistance arteries are more difficult to study and do not have such an apparent helical arrangement, although there are suggestions of its existence in the patterning of smooth muscle cells in the tunica media. MethodWe have employed confocal laser scanning microscopy (CLSM) and a relatively simple Fast Fourier Transform (FFT) based image analysis method to examine a collection of extended focus (z-projection) images of the tunica media of mouse superior mesenteric artery. A fluorescent nuclear stain (Syto 61) was used to identify smooth muscle cell orientation and arrangement. Thirty-six CLSM datasets representing the tunica media of mesenteric arteries taken from 12 C57/black mice were collected for analysis. ResultsMeasurements of Z-projection (extended focus) images, of the tunica media, were compared with measurements made on inverse FFT images where the high frequency information was removed. The results, of both measurement types, indicated the existence of an underlying basic helical arrangement of cells that has a pitch angle of 49°. 3D electron microscopy-based models of individual smooth muscle cells (from the tail artery) were generated to highlight their heterogeneity and orientational position within the tunica media. ConclusionInverse FFT images provide a more objective means of measuring cell organisation and therefore could be used in automated processes. Whilst we propose the existence of an underlying helical arrangement of smooth muscle cells, we do not discount the existence of other helices each with different angles, but these may be more difficult to detect and may extend radially (deep within the tunica media) as well as longitudinally.