Table I.

Assembly Dynamics of MT Ends in the Lamella of Newt Lung Epithelial Cells

		Fluorescent tubulin (present study)						VE-DIC
Parameter		+MT end, perpendicular* (n = 22 MTs, 13 cells)		+MT end, parallel* (n = 22 MTs, 13 cells)		−MT end‡ (n = 32 MTs, 13 cells)		+MT end (Vasquez et al., 1997)§		+MT end (Cassimeris et al., 1988)§
Growth rate  (μm/min)		4.5 ± 2.7		6.8 ± 3.9		–		4.9 ± 0.14 (270)		7.2 ± 0.3 (42)
Growth duration  (min)		0.6 ± 0.4		0.9 ± 0.7		–		1.06		1.2 ± 1.0
Shortening rate  (μm/min)		5.2 ± 4.3		7.6 ± 5.4		6.4 ± 5.9		14.3 ± 0.(161)		17.3 ± 0.7 (35)
Shortening duration  (μm/min)		0.5 ± 0.5		0.4 ± 0.2		0.7 ± 0.6		0.3		0.4 ± 0.3
Catastrophe frequency  (min-1)		1.57		0.61		–		0.96		0.84
Rescue frequency  (min-1)		2.31		2.59		–		3.12		2.64
Percentage time in  growth/shortening/pause		35.7/24.2/40.1		75.6/17.7/6.7		0/77.8/22.2		–		–

^* For comparison of assembly dynamics of parallel and perpendicular MTs, 22 MTs that grew perpendicular to the cell's edge and then underwent a bend and grew parallel to the cell edge were followed. Assembly parameters were determined for the periods during which the MT was perpendicular or parallel. The period when the MT was bending was discounted in the averages.  

^‡ Measurements include both shortening minus ends in which the MT breakage event that produced the minus end was observed as well as minus ends of unknown origin that depolymerized into the field of view from the direction of the cell center. MT orientation was not considered and stable minus ends that never exhibited shortening were not included in this analysis.  

^§ Values expressed as mean ± SEM; number of events measured in parentheses.