Table 1.
Measurements and classifications for cell volume and cell number
| Cell type | Strategy | Theoretical allometric exponent | Measured allometric exponent (slope a) | 95% CI for a | N | yint |
|---|---|---|---|---|---|---|
| Cell volume | ||||||
| Alveolar macrophages | i | 0 | 0.08 | (0.01,0.14) | 10 | 6.03 |
| Erythrocytes | i | 0* | 0 | (−0.02,0.03) | 74 | 4.25 |
| Fibroblasts | i | 0* | 0 | (−0.07,0.06) | 9 | 4.86 |
| Fibrocytes | i | 0* | 0.05 | (−0.06,0.16) | 9 | 3.50 |
| Glomerular epithelium | i | 0* | 0.05 | (−0.07,0.18) | 9 | 5.80 |
| Goblet cells | i | 0* | 0.07 | (−0.02,0.17) | 9 | 6.90 |
| Henle loop cells | i | 0* | 0.01 | (−0.03,0.05) | 9 | 6.39 |
| Hepatocytes | i | 0* | −0.03 | (−0.08,0.02) | 9 | 7.85 |
| Lung endothelial cells | i | 0* | 0 | (−0.06,0.06) | 10 | 5.99 |
| Lung interstitial cells | i | 0* | 0.06 | (−0.01,0.13) | 10 | 5.59 |
| Lung type I cells | i | 0* | 0.05 | (0.00,0.11) | 10 | 7.00 |
| Lung type II cells | i | 0* | 0 | (−0.06,0.06) | 10 | 6.14 |
| Proximal convoluted tubules | i | 0* | 0.04 | (0.00,0.07) | 9 | 7.16 |
| Sebaceous gland cells | i | 0* | 0.05 | (−0.03,0.12) | 9 | 7.34 |
| Adipocytes (dorsal wall of abdomen) | ii | 0.25 | 0.13 | (0.02,0.23) | 53 | 12.18 |
| Adipocytes (skin) | ii | 0.25* | 0.17 | (0.08,0.27) | 9 | 8.88 |
| Cerebellar granule neurons | ii | 3/4 × 1/4 = 0.19* | 0.14 | (0.06,0.22) | 9 | 3.56 |
| Cerebellar Purkinje neurons | ii | 3/4 × 1/4 = 0.19* | 0.18 | (0.14,0.23) | 19 | 7.20 |
| Number of cells | ||||||
| Alveolar macrophages | i | 1* | 0.96 | (0.86,1.06) | 10 | 11.94 |
| Lung endothelial cells | i | 1* | 1.00 | (0.90,1.09) | 10 | 14.32 |
| Lung interstitial cells | i | 1* | 1.08 | (0.97,1.19) | 10 | 13.11 |
| Lung type I cells | i | 1* | 0.95 | (0.80,1.09) | 10 | 13.12 |
| Lung type II cells | i | 1* | 0.98 | (0.92,1.14) | 10 | 12.73 |
| Adipocytes (dorsal wall of abdomen) | ii | 0.75* | 0.80 | (0.73,0.88) | 53 | 11.28 |
| Superior cervical ganglion neurons | ii | 0.75* | 0.68 | (0.51,0.85) | 7 | 6.52 |
Each cell type (column 1) is classified as most closely following either strategy i or ii (column 2) as defined in the text. Strategy i corresponds to cellular metabolic rate scaling with body mass, M (in grams), and invariant cell volume, Vc (in fl), whereas strategy ii corresponds to invariant cellular metabolic rate and scaling of cell volume. According to the classification, the theoretical values for the allometric exponent of either cell volume or of cell number, Nc, are listed (column 3). (See Discussion and SI Materials and Methods for an explanation of these theoretical expectations.) For the cell volume data, allometric scaling exponents, a, were estimated by fitting linear regression models of the form log(Vc) = alog(M) + yint. For the cell number data, exponents were estimated by fitting models of the form log(Nc) = alog(M) + yint. The 95% CI of the fitted slope, the number of data points used for model fitting, and the fitted intercept are reported for each of the models depicted in Figs. 2–4 and SI Fig. 5. The data strongly support the values based on the strategy (i or ii). The average allometric exponent for cell volume for the cells following strategy ii is 0.16 (95% CI: 0.14,1.18) and for cells following strategy i is 0.03 (95% CI: −0.03,0.09).
*Predictions that lie within the 95% CI of measurements.