PKC and myosin II activation levels are positively correlated. (A) Signaling cascades in this study. (B) F-Actin (left, red arrowheads point to contractile central actin bundles, yellow dashed line demarcates T zone) and ratio images of pRLC versus total RLC (right) of growth cones showing 5-HT–dependent (10 µM, 30 min) myosin II activation under control conditions. (C) PKC inhibition with Go alone (5 µM, 45 min) versus 5-HT+Go (Go 5 µM, 15-min pretreatment followed by 10 µM 5-HT in the continued presence of Go for 30 min). (D) PKC potentiation with DAGKi (5 µM, 45 min) versus 5-HT+DAGKi (DAGKi 5 µM, 15 min pretreatment followed by 10 µM 5-HT in the continued presence of DAGKi for 30 min). F-Actin visualized with phalloidin. Immunolabeling with pRLC antibody and total Aplysia RLC antibody after normal fixation. Ratio of pRLC versus total RLC after background subtraction, encoded in a linear pseudocolor lookup table (color bar). Scale bars: 5 µm. (E) Line scan analysis of the ratio of pRLC versus total RLC fluorescence in growth cones showing myosin II activation profiles in control versus 5-HT with PKC inhibition (Go) or potentiation (DAGKi) as in B–D above. Line scans (width = 50 pixels and length = 2× the P domain) sampled from front to rear of the growth cone. Two to four line scans were performed depending on the size of the growth cone. Light-colored points are raw data; solid lines are the population average. Number of growth cones sampled: nine control and eight 5-HT (top), seven Go and seven 5-HT+Go (middle), seven DAGKi and eight 5-HT+DAGKi (bottom). 27 measurements performed per condition, and data pooled across three independent experiments.