Are endothelial cells rich in filaments involved in the phenomenon of electrically induced stoppages of flow in frog capillaries?
The aim of this study was to determine the frequency of occurrence of the phenomenon in skin and muscle capillaries in both young and mature frogs and to examine the ultrastructure of endothelial cells found in these capillaries. Using microelectrode techniques, trains of pulses of durations up to 90 s, amplitudes -0.2 to -2.0 V, frequencies 10 to 64 Hz and pulse widths 5 to 50 msec were applied to microscopically visualized capillaries situated either in skin (knee region) or at the surface of a sartorius muscle in metamorphosed, intermediately aged or mature frogs. Reproducible flow stoppages induced by these trains of pulses occurred in 2.3%, 1.4% and 6.7% of all tested muscle capillaries and in 11.1%, 82.5% and 68.6% of all skin capillaries in the three age groups, respectively. Examinations of electron micrographs of very thin sections of both skin and muscle capillaries revealed that only 13 out of 47 (27.7%) and 4 out of 45 (8.9%) endothelial cells in these two tissues contained filament bundles. In light of these ultrastructural findings, the dramatically high occurrence of the phenomenon of electrically induced stoppages of flow in skin capillaries (in both intermediately aged and mature frogs) cannot be explained in terms of the hypothesis involving endothelial cells rich in filaments. It is concluded that caution must be exercised when interpreting this phenomenon in terms of the several microvascular responses which the electrical stimulation can elicit.
D000367:Age Factors; D000818:Animals; D001783:Blood Flow Velocity; D002196:Capillaries / Q000502:physiology*; D003599:Cytoskeleton / Q000648:ultrastructure; D004558:Electric Stimulation; D004727:Endothelium / Q000502:physiology* / Q000648:ultrastructure; D008854:Microscopy, Electron; D009132:Muscles / Q000098:blood supply; D011896:Rana temporaria; D012867:Skin / Q000098:blood supply