Determination of the Volume and Surface Area of Tetrahymena pyriformis, and their Relationship to Endocytosis

SYNOPSIS Methods are described for the determination of the mean cellular volume and surface area of Tetrahymena pyriformis GL by direct microscopic measurement or by Coulter counter. The results are compared and discussed. It is suggested that the latter is the more accurate method of estimation. Fed cells showed a bimodal size distribution by Coulter counter determination and had a mean volume of 10,000–11,000 μM3, whereas cells which had been starved for 1 or 2 days showed a unimodal distribution and had mean cellular volumes of ∼ 1,600 and 1,200 μ3 respectively. The corresponding mean surface areas were ∼ 1,900, 550 and 450 μM2 respectively. The discrepancy between the results of the 2 methods of estimation was greater with starved than with fed cells because of the greater asymmetry of the former. Continued cell division during the early part of the starvation period had a considerable reducing effect upon the mean cellular volume, but other unidentified factors were also important in producing the observed diminution in volume. Comparison of the mean surface areas of starved cells with previously recorded rates of membranous utilization in endocytosis upon refeeding indicate that insufficient cell membrane was present to maintain the rates of vacuole formation observed.