FUNCTIONAL CAPILLARY ORGANIZATION IN STRIATED-MUSCLE

In striated muscle, capillaries occur as independent network groups. Network architecture was quantitated in cremaster muscle of pentobarbital sodium-anesthetized hamsters in three age groups [51 +/- 1 (SE), 65 +/- 1, and 79 +/- 1 days old]. We observed that networks consist of independent subgroups of capillaries, called modules. Module architecture did not vary significantly with age during maximal dilation (Max, 10(-4) M adenosine): tissue area (A) = 1.87 +/- 0.16, 1.19 +/- 0.13, and 1.81 +/- 0.3 x 10(5) mu m(2); total segment length (Sigma L)= 3.07 +/- 0.23, 2.15 +/- 0.21, and 3.02 +/- 0.45 x 10(3) mu m; and segment number (N) = 14.5 +/- 1.1, 9.9 +/- 1.1, and 12.6 +/- 1.6, at ages 51, 65, and 79 days, respectively. Max module architecture was not different at 65 days of age at a second site of known higher O-2 inflow: A = 2.03 +/- 0.32 x 10(5) mu m(2); Sigma L = 3.07 +/- 0.47 x 10(3) mu m; and N = 13.1 +/- 2.1. During control conditions (Rest) there was also no significant difference with age: A = 1.68 +/- 0.18, 1.15 +/- 0.19, and 1.64 +/- 0.24 x 10(5) mu m(2); Sigma L = 2.31 +/- 0.23, 1.91 +/- 0.33, and 2.82 +/- 0.37 x 10(3) mu m; N = 10.2 +/- 1.0, 7.8 +/- 1.3, and 11.0 +/- 1.4, at ages 51, 65, and 79 days, respectively. High O-2 inflow modules were significantly different during Rest at 65 days of age: A = 2.21 +/- 0.29 x 10(5) mu m(2), Sigma L = 3.34 +/- 0.52 x 10(3) mu m, and N = 12.8 +/- 2.0. The two-dimensional capillary length density (Sigma L/A) is invariant with age: 0.018 +/- 0.001, 0.018 +/- 0.001, and 0.020 +/- 0.001 mu m(-1) at ages 51, 65, and 79 days, respectively. Networks are significantly different with age due to a decreased number of modules per network (Max: 5.7 +/- 1.2, 3.2 +/- 0.5, 2.6 +/- 0.3 modules at ages 51, 65, and 79 days, respectively). High O-2 inflow networks were significantly larger at 65 days of age (Max: 6.5 +/- 0.3 modules). Thus modules are an invariant unit of network architecture, and networks are larger in areas of expected higher flow due to the addition of modules. Differences between high and law O-2 inflow networks at Rest suggest possible differences in regulatory mechanisms.