In vitro effects of PAF on venous endothelial cell actin disposition

Store-operated calcium entry promotes shape change in pulmonary endothelial cells expressing Trp1

Activation of Ca2+ entry is known to produce endothelial cell shape change, leading to increased permeability, leukocyte migration, and initiation of angiogenesis in conduit-vessel endothelial cells. The mode of Ca2+ entry regulating cell shape is unknown. We hypothesized that activation of store-operated Ca2+ channels (SOCs) is sufficient to promote cell shape change necessary for these processes. SOC activation in rat pulmonary arterial endothelial cells increased free cytosolic Ca2+ that was dependent on a membrane current having a net inward component of 5.45 +/- 0.90 pA/pF at -80 mV. Changes in endothelial cell shape accompanied SOC activation and were dependent on Ca2+ entry-induced reconfiguration of peripheral (cortical) filamentous actin (F-actin). Because the identity of pulmonary endothelial SOCs is unknown, but mammalian homologues of the Drosophila melanogaster transient receptor potential (trp) gene have been proposed to form Ca2+ entry channels in nonexcitable cells, we performed RT-PCR using Trp oligonucleotide primers in both rat and human pulmonary arterial endothelial cells. Both cell types were found to express Trp1, but neither expressed Trp3 nor Trp6. Our study indicates that 1) Ca2+ entry in pulmonary endothelial cells through SOCs produces cell shape change that is dependent on site-specific rearrangement of the microfilamentous cytoskeleton and 2) Trp1 may be a component of pulmonary endothelial SOCs.

Possible involvement of microtubules in platelet-activating factor-induced increases in microvascular permeability in vitro

The blood vessels of the rat small intestine were perfused in vitro with a gelatin-containing physiological salt solution (GPSS). The addition of platelet-activating factor (PAF, 5 microM), podophyllotoxin (50 microM), colcemid (50 microM), or nocodazole (50 microM) to the GPSS for 5 min caused an increase in vascular permeability. This was manifested as an increased trapping of circulating colloidal carbon (CC) within the walls and was assessed using semiautomated image analysis. Pretreatment for 10 min with taxol (5 microM) in the perfusate significantly reduced the permeability-enhancing effects of all four agonists. Since podophyllotoxin, colcemid, and nocodazole are all microtubule-disrupting agents, and since taxol is a microtubule-stabilizing agent, these results suggest that microtubules are involved in the response of the microvessels to PAF. An explanation based on "tensegrity" or "force-counterbalance" is put forward to account for these findings.

An in vitro method for assessing the effects of pro-inflammatory and anti-inflammatory compounds on microvascular permeability in the rat small intestine

A method is described in which the blood vessels of the rat mesentery and small intestine were perfused for 15 min in vitro with a gelatin-containing physiological salt solution. Colloidal carbon (CC) was then added to the perfusate. In control preparations, very little CC was trapped in the microvessels of the small intestine, but if platelet-activating factor (PAF) was added for 5 min before the infusion of CC, many microvessels were "blackened." When the PAF antagonist BN52021 was included in the perfusate throughout, the "blackening" response to PAF was significantly reduced. Using micrographs of fixed specimens of gut, the amounts of "blackening" in the microvessels of the villi, the crypts of Lieberkuhn, and the muscularis were assessed using semiautomated image analysis. The technique provides a means of investigating the effects on microvascular permeability of pro-inflammatory and anti-inflammatory compounds. It is particularly useful for testing substances which, because of their highly toxic nature, cannot be administered systemically in vivo.