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This study demonstrates that aequorin, a luminescent natural dye, is useful for vascular cell intracellular [Ca.sup.2+] concentration ([[[Ca.sup.2+]].sub.i]) determination. A new single-photon counting technique was developed to resolve the effects of fluid flow shear stress on [[[Ca.sup.2+]].sub.i] in human aortic smooth muscle cells (HASMCs). Confluent HASMCs were grown on petri dishes loaded with aequorin. Then the dishes were placed in a luminometer chamber after the physiological level of shear stress was applied to the HASMC surfaces. The chamber was housed inside a highly sensitive photomultiplier tube. It detected ultraweak photon emission in response to the [[[Ca.sup.2+]].sub.i] transient. In the presence of 2.0 mM extracellular [Ca.sup.2+], a shear stress of 12 dyn/[cm.sup.2], applied for 60 s to the top surface of the HASMC monolayer, elicited a sharp increase in [[[Ca.sup.2+]].sub.i]. [DOI: 10.1115/1.2264396] Keywords: ultraweak photon-counting, smooth muscle cells, shear stress, intracellular [Ca.sup.2+], biophoton

The internal elastic lamina (IEL), which separates the arterial intima from the media, affects macromolecular transport across the medial layer. In the present study, we have developed a two-dimensional numerical simulation model to resolve the influence of the IEL on convective-diffusive transport of macromolecules in the media. The model considers interstitial flow in the medial layer that has a complex entrance condition because of the presence of leaky fenestral pores in the IEL. The IEL was modeled as an impermeable barrier to both water and solute except for the fenestral pores that were assumed to be uniformly distributed over the IEL. The media were modeled as a heterogeneous medium composed of an array of smooth muscle cells (SMCs) embedded in a continuous porous medium representing the interstitial proteoglycan and collagen fiber matrix. Results for ATP and low-density lipoprotein (LDL) demonstrate a range of interesting features of molecular transport and uptake in the media that are determined by considering the balance among convection, diffusion, and SMC surface reaction. The ATP concentration distribution depends strongly on the IEL pore structure because ATP fluid-phase transport is dominated by diffusion emanating from the fenestral pores. On the other hand, LDL fluid-phase transport is only weakly dependent on the IEL pore structure because convection spreads LDL laterally over very short distances in the media. In addition, we observe that transport of LDL to SMC surfaces is likely to be limited by the fluid phase (surface concentration less than bulk concentration), whereas ATP transport is limited by reaction on the SMC surface (surface concentration equals bulk concentration). smooth muscle cell; low-density lipoprotein; adenosine 5'-triphosphate; numerical analysis

Flow through internal elastic lamina affects shear stress on smooth muscle cells (3D simulations). Am J Physiol Heart Circ Physiol 282: H576-H584, 2002. First published October 25, 2001; 10.1152/ajpheart.00751.2001.--We describe a three-dimensional numerical simulation of interstitial flow through the medial layer of an artery accounting for the complex entrance condition associated with fenestral pores in the internal elastic lamina (IEL) to investigate the fluid mechanical environment around the smooth muscle cells (SMCs) right beneath the IEL. The IEL was modeled as an impermeable barrier to water flow except for the fenestral pores, which were assumed to be uniformly distributed over the IEL. The medial layer was modeled as a heterogeneous medium composed of a periodic array of cylindrical SMCs embedded in a continuous porous medium representing the interstitial proteoglycan and collagen matrix. Depending on the distance between the IEL bottom surface and the upstream end of the proximal layer of SMCs, the local shear stress on SMCs right beneath the fenestral pore could be more than 10 times higher than that on the cells far removed from the IEL under the conditions that the fenestral pore diameter and area fraction of pores were kept constant at 1.4 [micro]m and 0.05, respectively. Thus these proximal SMCs may experience shear stress levels that are even higher than endothelial cells exposed to normal blood flow (order of 10 dyn/[cm.sup.2]). Furthermore, entrance flow through fenestral pores alters considerably the interstitial flow field in the medial layer over a spatial length scale of the order of the fenestral pore diameter. Thus the spatial gradient of shear stress on the most superficial SMC is noticeably higher than computed for endothelial cell surfaces. computer simulation; fenestral pore

The fully developed periodic laminar flow of incompressible Newtonian fluids through a pipe of circular cross section, which is coiled in a circle, was simulated numerically. The flow patterns are characterized by three parameters: the Womersley number Wo, the Dean number De, and the amplitude ratio [Beta]. The effect of these parameters on the flow was studied in the range 2.19 [less than or equal to] Wo [less than or equal to] 50.00, 15.07 [less than or equal to] De [less than or equal to] 265.49 and 0.50 [less than or equal to] [Beta] [less than or equal to] 2.00, with the curvature ratio [Delta] fixed to be 0.05. The way the secondary flow evolved with increasing Womersley number and Dean number is explained. The secondary flow patterns are classified into three main groups: the viscosity-dominated type, the inertia-dominated type, and the convection-dominated type. It was found that when the amplitude ratio of the volumetric flow rate is equal to 1.0, four to six vortices of the secondary flow appear at high Dean numbers, and the Lyne-type flow patterns disappear at [Beta] [greater than or equal to] 0.50.

Interstitial flow through the internal elastic lamina affects shear stress on arterial smooth muscle cells. Am J Physiol Heart Circ Physiol 278: H1589-H1597, 2000.--Interstitial flow through the tunica media of an artery wall in the presence of the internal elastic lamina (IEL), which separates it from the subendothelial intima, has been studied numerically. A two-dimensional analysis applying the Brinkman model as the governing equation for the porous media flow field was performed. In the numerical simulation, the IEL was modeled as an impermeable barrier to water flux, except for the fenestral pores, which were uniformly distributed over the IEL. The tunica media was modeled as a heterogeneous medium composed of a periodic array of cylindrical smooth muscle cells (SMCs) embedded in a fiber matrix simulating the interstitial proteoglycan and collagen fibers. A series of calculations was conducted by varying the physical parameters describing the problem: the area fraction of the fenestral pore (0.001-0.036), the diameter of the fenestral pore (0.4-4.0 [micro] m), and the distance between the IEL and the nearest SMC (0.2-0.8 [micro] m). The results indicate that the value of the average shear stress around the circumference of the SMC in the immediate vicinity of the fenestral pore could be as much as 100 times greater than that around an SMC in the fully developed interstitial flow region away from the IEL. These high shear stresses can affect SMC physiological function. fenestral pore; numerical analysis