Tyrosine phosphorylation following alterations in arteriolar intraluminal pressure and wall tension

Arterioles respond to increased transmural pressure with myogenic constrict ion. The present study investigated the role of tyrosine phosphorylation in myogenic activity. Cannulated segments of a rat cremaster arteriole were f ixed under pressure, followed by incubation with fluorescein isothiocyanate (FITC)-conjugated anti-phosphotyrosine. Smooth muscle cell fluorescence in tensity was measured with the use of confocal laser-scanning microscopy. An ti-phosphotyrosine fluorescence intensity in muscle cells of arterioles mai ntained at 100 mmHg was reduced by the tyrosine kinase inhibitor tyrphostin A47 (30 muM) and increased by the tyrosine phosphatase inhibitor pervanada te (100 muM). In time-course experiments, anti-phosphotyrosine fluorescence increased slowly (over 5 min) after an acute increase in intraluminal pres sure, and was dissociated from myogenic contraction (within 1 min). In cont rast, angiotensin II (0.1 muM) caused rapid constriction and increased tyro sine phosphorylation. Anti-phosphotyrosine fluorescence was also pressure d ependent (10-100 mmHg). Abolition of myogenic activity, either through remo val of extracellular Ca2+, or exposure to verapamil (5 muM) or forskolin (0 .1 muM) caused a further increase in antiphosphotyrosine fluorescence. We c onclude that transmural pressure and/or wall tension in arterioles causes i ncreased tyrosine phosphorylation; however, this is not involved in the acu te phase of myogenic constriction but may be involved in later responses, s uch as sustained myogenic tone or mechanisms possibly related to growth.