Chemotactic reorientation of granulocytes stimulated with micropipettes containing fMet-Leu-Phe.

Human granulocytes were stimulated by means of a micropipette, with an orifice of about 0.2 micrometer in diameter, which contained fMet-Leu-Phe at a concentration of 10(-5) M. The cells were reorientated by extending lamellipodia towards the source of the attractant, often within less than 10 s. Any part of the granulocyte, from the front to the tip of the tail, could be stimulated to produce new lamellipodia. Usually, but not always, this response occurred at the side of the cell nearest to the micropipette. Cells stimulated from behind responded in one of the following ways: (1) Cells that maintained their polarity extended new lamellipodia at one side of the leading front and reorientated by moving in a U-turn towards the micropipette. Occasionally, the leading front was split because one part of the front tried to make a left-hand and the other a right-hand turn. (2) Formation of lamellipodia at the leading front was arrested and new lamellipodia were formed at the tail instead, indicating reversal of polarity. The result was an immediate change in the direction of locomotion by about 180 degrees. (3) A combination of the first 2 forms of behaviour was observed occasionally. Transiently, lamellipodia were extended from cell surface areas both close to and distant from the micropipette. These observations show that parts of a cell can respond independently to chemotactic gradients by extending lamellipodia towards the source of the attractant. The phenomenon can easily be explained by assuming that a temporal change of attractant concentration is recognized.