Static and dynamic components in the vascular myogenic response to passive changes in length as revealed by electrical and mechanical recordings from the rat portal vein.

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Abstract
The effects of static and dynamic passive stretch and shortening on electrical activity and active force were analyzed in the isolated rat portal vein. Static stretch by 40% of muscle length evoked moderate excitatory effects with enhanced mechanical activity and an average increase in spike discharge of 12% above the control value of 55 plus or minus 2.6 spikes/min. The dynamic responses studied at various rates of length change (dL/dt) over the range between minus 12 and plus 12 mm/min, i.e., minus 3 and plus 3% muscle length/sec, were much more pronounced. Active force and spike activity showed graded increases with increasing rates of stretch. The electrical activity reached a value of 180 spikes/min (approximately equal to 325% of control) at 5 mm/min; this frequency was then maintained for stretch rates up to 12 mm/min. Mechanical activity during stretch was further reinforced by the shift along the length-tension diagram. Passive shortening at rates from minus 1 to minus 12 mm/min caused graded dec...