Tyrosine phosphorylation modulates arteriolar tone but is not fundamental to myogenic response

The present study investigated the role of protein tyrosine phosphorylation in myogenic responsiveness of rat skeletal muscle arterioles. Arteriolar s egments were cannulated and pressurized without intraluminal flow. All vess els studied developed spontaneous tone and demonstrated significant myogeni c constriction to step changes in pressure with a resultant increase in myo genic tone over an intraluminal pressure range of 50-150 mmHg. Step increas es in intraluminal pressure from 50 to 120 mmHg caused a rapid and sustaine d elevation in intracellular [Ca2+], as measured using fura 2. Vessels with myogenic tone dilated in response to tyrosine kinase inhibitors genistein (10 or 30 mu M) and tyrphostin A47 (10 or 30 mu M) and constricted to the t yrosine phosphatase inhibitor pervanadate (1 or 10 mu M). Despite the dilat or effect, myogenic reactivity was not blocked by the inhibitors. Daidzein (10 mu M), a compound structurally similar to genistein but without tyrosin e kinase-inhibiting activity, did not alter vessel tone or myogenic respons es. Preincubation of arterioles with genistein or tyrphostin A47 did not si gnificantly alter baseline arteriolar [Ca2+], and neither drug reduced the increase in [Ca2+] following an acute increase in intraluminal pressure. Co nstriction induced by pervanadate (10 mu M) was not accompanied by a signif icant increase in intracellular [Ca2+], even though removal of extracellula r Ca2+ reversed the constriction Examination of smooth muscle tyrosine phos phorylation, using a fluorescent phosphotyrosine antibody and confocal micr oscopy, showed that increased intraluminal pressure resulted in an increase in anti-phosphotyrosine fluorescence. Because manipulation of tyrosine kin ase activity was found to alter vessel diameter, these data support a:role for tyrosine phosphorylation in modulation of arteriolar tone. However, the results indicate that acute arteriolar myogenic constriction does not requ ire tyrosine phosphorylation.