Intraluminal flow increases vascular tone and 45Ca2+ influx in the rabbit facial vein.

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Abstract
The buccal segment of the rabbit facial vein exhibits a high level of myogenic tone in vitro that develops only in stretched vessel segments between 33 degrees and 44 degrees C. The infusion of physiological salt solution into the lumen of 2-mm-long rabbit facial vein segments induced a flow rate-dependent increase in wall tone, both in the presence (37 degrees C) and absence (30 degrees C) of myogenic tone. In calcium-free physiological solution with EGTA, neither flow nor stretch-induced tone was observed. This flow-induced contraction was associated with an increase in 45Ca2+ unidirectional influx and net uptake. These measurements correlated positively with the level of the associated constrictor responses, both in the presence or absence of myogenic tone. The mean contractile responses to flow (10 and 40 microliters/min), stretch, and histamine (1 microM) were 13%, 28%, 24%, and 33% of the tissue maximal response, respectively. When 45Ca2+ influx was expressed in relation to the force development (45Ca2+ influx per milligram), the amount of calcium entry was dependent on the stimulus. Values for 45Ca2+ influx per milligram in response to flow (10 and 40 microliters/min) and to histamine (1 microM) were not significantly different. The value was significantly lower for the response to stretch. On the other hand, 45Ca2+ net uptake, when expressed per unit force, was similar in response to flow (10 and 40 microliters/min), histamine (1 microM), and stretch.(ABSTRACT TRUNCATED AT 250 WORDS)