Table 1.
Surface expansion induced by the [Ca2+]i rise after DM-nitrophen photolysis, and resting distribution of secretory organelles in wild-type and defective PC12 cells
| Wild-type PC12
|
PC12-27
|
||
|---|---|---|---|
| SV | LV | V27 | |
| Cell capacitance* | |||
| Surface expansion, percent ± SD of the resting plasmalemma | 13 ± 5.1% | 10 ± 7.1% | 19.1 ± 8.8% |
| Vescicle morphometry, number per square micrometer and percent surface correspondance to the resting plasmalemma† | |||
| Docked | 3.2 ± 1.1, 2.5% | 5.2 ± 0.8, 18.1% | 0.5 ± 0.2, 0.4% |
| In the juxtaplasmalemma layer, 0.5 μm thick | 15.3 ± 2, 12.0% | 2.6 ± 0.2, 8.9% | 5.3 ± 0.8, 4.2% |
Surface expansion of resting wild-type and defective PC12 cells was assessed directly from capacitance measurements. V27 in the PC12-27 column refers to the sum of the two capacitance components with time constants of ∼50 msec and 1 sec observed in the defective clone.
SV, LV, and V27 profiles were counted in groups of pictures from qf-fd samples of PC12 and PC12-27 cells printed at 50,000×. LVs were recognized easily because of their peculiar features; their diameter, as established from measurements in a group of 55 organelles that appear equatorily sectioned, was 105 ± 5 nm. Profiles taken for SVs and V27 were discrete, round, or moderately elongated, with dense content and transverse size varying from 40 to 60 nm. Inclusion in the population of transverse sections of tubules (ER, endosomes) could not be excluded. Profiles given as docked appeared in contact with the plasmalemma, either directly or via short bridges. The overall length of the cell profile investigated amounted to 227 and 95 μm for wild-type PC12 and PC12-27, respectively. The number of vesicles per cell surface area was calculated from the data of electron micrographs as recommended by Weibel et al. (20), assuming the average section thickness to be 45 nm. Correspondance of vesicle cumulative surface to the resting plasmalemma was calculated assuming the average surface of single SV and V27, on the one hand, and LV, on the other hand, to be 7,850 and 35,000 nm2, respectively.