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 wi th a gelatin-containing physiological salt solution (GPSS). The additi on of platelet-activating factor (PAF, 5 muM), podophyllotoxin (50 muM ), colcemid (50 muM), or nocodazole (50 muM) to the GPSS for 5 min cau sed an increase in vascular permeability. This was manifested as an in creased trapping of circulating colloidal carbon (CC) within the walls and was assessed using semiautomated image analysis. Pretreatment for 10 min with taxol (5 muM) in the perfusate significantly reduced the permeability-enhancing effects of all four agonists. Since podophyllot oxin, colcemid, and nocodazole are all microtubule-disrupting agents, and since taxol is a microtubule-stabilizing agent, these results sugg est that microtubules are involved in the response of the microvessels to PAF. An explanation based on ''tensegrity'' or ''force-counterbala nce'' is put forward to account for these findings.