Electrical and mechanical responses of rat saphenous vein to short-term pressure load

The magnitude and mechanism of myogenic response of vascular smooth muscle (SM) in rat distal saphenous vein was assessed from SM membrane potential (Em) measured in situ and in vitro with glass microelectrodes and from active and passive stress and strain calculated from changes in vessel diameter measured in vitro via videomicroscopy. Elevation of intraluminal pressure from 2.2 +/- 0.2 (SE) mmHg (control) to 15 +/- 0.8 mmHg for 1 h in a series of in vitro vessel segments perfused with physiological salt solution at 0.2 ml/min induced a maintained and reversible depolarization of 18 +/- 0.9 mV. A 7.6 +/- 0.4-mmHg pressure increase induced a 12.9 +/- 1.2-mV depolarization in a second series. In a third series, 5-mmHg pressure increments induced significant increments in active isometric stress and isobaric strain. Opening an acute, reversible in situ femoral artery to saphenous vein shunt caused a 4- to 5-mmHg venous pressure elevation, a 10-fold increase in venous blood flow, and a 12.1 +/- 0.9-mV venous SM depolarization. Thus a short-term pressure load causes sustained, reversible venous SM cell depolarization both in vitro and in situ, coupled with active strain and stress generation in the vein wall. These results support our hypothesis that SM of peripheral veins can contribute to an intrinsic capacity autoregulation.