Bioluminescent imaging was used to track the viability of luciferase transfected L929 cells in poly(hydroxyethyl methacrylate-co-methyl methacrylate) (HEMA-MMA) microcapsules. Bioluminescence, as determined by Xenogen imaging after addition of luciferin to microcapsules in vitro, increased with time, consistent with an increase in cell number. Capsules were suspended in Matrigel and injected subcutaneously. The bioluminesence in vivo increased over the first 3 weeks and then decreased, both with and without the delivery of mVEGF(164) (1.2 ng/24 h/200 microcapsules in vitro); VEGF delivery was from microencapsulated doubly transfected cells (both luciferase and mVEGF(164)). VEGF delivery was sufficient to generate a greater number of vascular structures, but this did not result in the expected increase in microencapsulated cell viability. Interestingly, the number of vessels at day 28 was less than at day 21, consistent with what would be an expected reduction in VEGF secretion when cell viability is lost. The results presented here do not support the hypothesis that transfection of microencapsulated cells with VEGF is sufficient to correct the oxygen transport limitation, at least with this type of tissue engineering construct. On the other hand, bioluminescent imaging proved to be a useful method of monitoring microencapsulated cell viability over many weeks in vivo.

Acetylcholine (ACh) binding to atrial muscarinic receptors activates an inwardly rectifying K+ current (IK[ACh]) via a pertussis toxin-sensitive GTP-binding protein (GK). The muscarinic K+ channel (termed GIRK1) has been cloned, and the nucleotide sequence contains nine consensus sites for protein kinase C (PKC) phosphorylation (16). Dephosphorylation of the muscarinic K+ channel has been implicated in rapid IK[ACh] desensitization in the presence of agonist (13). Staurosporine is a widely used membrane-permeant inhibitor of PKC and other protein kinases (7), including G protein-coupled receptor kinases. We investigated the role of phosphorylation in the regulation of IK[ACh] by examining the effect of a variety of protein kinase inhibitors. Staurosporine produced a rapid and reversible dose-dependent decrease in IK[ACh], activated by either GTP or guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S). Other PKC inhibitors, including calphostin C and K-252b, were without effect on GTP gamma S-activated IK[ACh]. In excised patches of atrial membrane under nonphosphorylating conditions (0 ATP, 1 mM 5'-adenylylimidodiphosphate), staurosporine reversibly reduced muscarinic K+ channel activity without altering single-channel current amplitude. These results suggest that staurosporine inhibits IK[ACh] by a mechanism independent of intracellular protein kinases.

This protocol describes the fabrication of a type of micro-tissues called modules. The module approach generates uniform, scalable and vascularized tissues. The modules can be made of collagen as well as other gelable or crosslinkable materials. They are approximately 2 mm in length and 0.7 mm in diameter upon fabrication but shrink in size with embedded cells or when the modules are coated with endothelial cells. The modules individually are small enough that the embedded cells are within the diffusion limit of oxygen and other nutrients but modules can be packed together to form larger tissues that are perfusable. These tissues are modular in construction because different cell types can be embedded in or coated on the modules before they are packed together to form complex tissues. There are three main steps to making the modules: neutralizing the collagen and embedding cells in it, gelling the collagen in the tube and cutting the modules and coating the modules with endothelial cells.

Modular tissue engineering is a strategy to create scalable, self-assembling, three-dimensional (3D) tissue constructs. This strategy was used to deliver endothelial-like cells derived from bone marrow mesenchymal stromal cells (EL-MSCs) to locally induce vascularization. First, tissue engineered modules were formed, comprising EL-MSCs and collagen-based cylinders. Seven days of module culture in a microfluidic chamber under continuous flow resulted in the formation of interstices, formed by random packing of the modules, which served as channels and were lined by the EL-MSCs. We observed maintenance of the endothelial phenotype of the EL-MSCs, as demonstrated by CD31 staining, and the cells proliferated well. Next, collagen modules covered with EL-MSCs, with or without embedded MSCs, were implanted subcutaneously in immune-compromised SCID/Bg mice. After 7 days, CD31-positive vessels were observed in the samples. These data demonstrate the feasibility of EL-MSCs coated collagen module as a strategy to locally stimulate angiogenesis and vasculogenesis. Copyright © 2013 John Wiley & Sons, Ltd.