Abstract-Small-artery responses to vasoconstrictor agonists are important for vascular function. To investigate the signaling pathways involved in contraction, we studied the activation and regulation of p38 mitogen-activated protein kinases (p38MAPKs) and heat shock protein (HSP) kinase by endothelin and noradrenaline in rat mesenteric arteries. Both vasoconstrictors activated p38␣ and/or p38␤ but not p38␥ or p38␦, leading to increased HSP kinase activity. p38MAPK activation by noradrenaline was maximum between 2 and 10 minutes and was wholly dependent on calcium influx but insensitive to the tyrosine kinase inhibitor herbimycin A. In contrast, endothelin induced a biphasic response, with activation at 2 and 10 minutes. The early activity was wholly dependent on calcium influx and inhibited by herbimycin A. The later activity was only 50% calcium dependent, was insensitive to herbimycin A, but was 50% inhibited by genistein, a nonselective tyrosine kinase inhibitor. With both agonists, p38MAPK activity returned to basal by 30 minutes. SB203580, a p38MAPK inhibitor, blocked agonist-induced HSP kinase activity, and herbimycin A inhibited activation by endothelin but not by noradrenaline. In addition, SB203580 inhibited noradrenaline-induced contraction but had little effect on contraction to endothelin. These data show that vasoconstrictors use different upstream activators of p38MAPK in vascular tissue and that the p38MAPK pathway is selectively implicated in the contractile response to noradrenaline in small arteries. Key Words: vasoconstrictors Ⅲ vascular smooth muscle Ⅲ heat shock proteins Ⅲ signal transduction V ascular tone is an important determinant of peripheral resistance and blood pressure, and abnormalities in small-artery contractility contribute to pathological states such as vasospasm and hypertension. 1 The major mechanism of smooth muscle contraction is an increase in cytoplasmic calcium and phosphorylation of the regulatory light chains of myosin. However, there is considerable evidence indicating that vasoconstrictors activate multiple ancillary pathways that modulate the contractile response (see reviews 2,3 ). Among the many pathways activated, protein kinase C, 2 Rho family G proteins, 3,4 nonreceptor tyrosine kinases, 5 and extracellular signal-regulated kinases (ERK1/2) 2,6 have been shown to play a role in smooth muscle contraction. Recently, stressactivated protein kinases have also been implicated in sustained contraction through regulation of the phosphorylation of heat shock protein (HSP) 27. 7 HSP27 belongs to a family of small HSPs that includes HSP20, myotonic dystrophy kinase-binding proteins, and crystallins. 8 Increased phosphorylation of HSP27 has been reported in response to a variety of vasoconstrictors in smooth muscle, 9 -12 and inhibition of HSP27 phosphorylation or interference with its function reduces contraction. 9 HSPs may also play a role in vascular diseases such as hypertension. For instance, stress-induced hypertension in rats increased the expression and phos...

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In rat mesenteric arteries, noradrenaline (NA) induces a time-dependent increase in tyrosine phosphorylation of a number of proteins, one of which was identified as paxillin. NA-induced protein tyrosine phosphorylation was ablated by tyrosine kinase inhibition, virtually unaffected by protein kinase C (PKC) inhibition or PKC downregulation and was mimicked by KCl. NA also caused a time-dependent activation of the extracellular signal-regulated kinases (ERK)1 and ERK2. These responses were blocked by the ERK-activating kinase (MEK) inhibitor PD98059 and by tyrosine kinase inhibition but only modestly attenuated by PKC downregulation or inhibition. Pretreatment of cannulated mesenteric arteries (50 mm Hg internal pressure) with PD98059 significantly reduced the contractile responsiveness of the vessels to NA (1.56 ± 0.14 µM, EC₅₀ control; 3.32 ± 0.49 µM, EC₅₀ + PD98059, p < 0.01). Thus, NA induces time-dependent increases in protein-tyrosine phosphorylation and ERK activation in rat mesenteric arteries that could suggest a role for Ca²⁺-dependent non-receptor tyrosine kinases and ERKs in the response of small arteries to NA. In addition, the modulation of NA-induced mesenteric artery contraction by inhibition of the MEK/ERK pathway further implicates ERK in the regulation of, though perhaps not the mediation of NA-induced small artery contraction.

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