Longitudinal and lateral movement of titin-eGFP within the sarcomere. (A) Bleaching of 3 or 8 consecutive sarcomeres in embryonic cardiomyocytes was used to study longitudinal (white arrows) and lateral (open arrows) mobility of titin-eGFP. Titin-eGFP dynamics was monitored for 14 h. Bar, 10 µm. (B and C) Lateral and longitudinal movement of titin-eGFP were equally efficient as demonstrated by the plot of fluorescence intensity vs. time after photobleaching of 3 or 8 sarcomeres (3 sarcomeres, n = 4; 8 sarcomeres, n = 3). (D and E) The titin-eGFP mobile fractions were independent from the shape and area of photobleaching, whereas the half-fluorescence recovery increases with the size of the bleached area (3 sarcomeres, n = 4; 8 sarcomeres, n = 3). Error bars indicate SEM.