INTRALUMINAL FLOW INCREASES VASCULAR TONE AND CA-45(2+) INFLUX IN THE RABBIT FACIAL VEIN

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 Ca-45(2+) 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-mu-l/min), stretch, and histamine (1-mu-M) were 13%,28%, 24%, and 33% of the tissue maximal response, respectively. When Ca-45(2+) influx was expressed in relation to the force development (Ca-45(2+) influx per milligram), the amount of calcium entry was dependent on the stimulus. Values for Ca-45(2+) influx per milligram in response to flow (10 and 40-mu-l/min) and to histamine (1-mu-M) were not significantly different. The value was significantly lower for the response to stretch. On the other hand, Ca-45(2+) net uptake, when expressed per unit force, was similar in response to How (10 and 40-mu-l/min), histamine (1-mu-M), and stretch. We conclude that How-induced contraction in the rabbit facial vein is associated with Ca2+ entry into the smooth muscle cells through a pathway that may be different from that associated with stretch-activated contraction.