AChR movement within or near pre-patterned clusters. Consecutive time-lapse frames (separated by 2.5s) were pseudo-colored in red and green and superimposed. Yellow dots: immobile BBQs; paired green/red dots (arrows): mobile BBQs; un-paired green or red dots: BBQs that blinked during the recording and thus only one color was recorded. (a, a') A well-developed cluster on a 3-day old muscle cell shown by Alexa488-BTX (a) and BBQ (a') labeling with the blue lines outlining the lower edge of this hot spot. While most of the receptors within the cluster were immobile (yellow dots), those outside were mobile (small arrows). (b, b' and c, c') Development of an AChR cluster (arrowhead) in a 1-day old culture during a 3 hr recording period. b, c: Alexa488-BTX; b', c': BBQ.