Stretch-dependent activation and desensitization of mitogen-activated protein kinase in carotid arteries

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Abstract
Arterial smooth muscle stretch is an important physiological modulator of vascular function. To identify intracellular processes altered during muscle stretch, we found previously that extracellular signal-regulated kinase-mitogen-activated protein kinase (MAPK) activity increased in response to the application of mechanical loads. In the present study, stretch-dependent activation of MAPK in porcine carotid arteries was investigated as was the phosphorylation of the thin filament-binding protein caldesmon, which is known to be a substrate for the kinase in fully differentiated smooth muscle. MAPK activity was 67 pmol ⋅ min−1⋅ mg protein−1in unloaded muscle strips immediately after attachment to force transducers and 139 pmol ⋅ min−1⋅ mg protein−1within 30 s of muscle stretch. When muscle strips were continually stretched, MAPK activity remained elevated for ∼2 h and then decreased over 16 h to 16 pmol ⋅ min−1⋅ mg protein−1. When muscle strips were stretched and then unloaded, MAPK activity decreased within 1 h to the level present in the muscle before the stretch. These effects of muscle stretch on MAPK activity were additive to the effects of KCl or phorbol ester stimulation and were partially inhibited by reducing extracellular Ca2+. Eliminating extracellular Ca2+had no effect on phorbol 12,13-dibutyrate (PDBu)-dependent contractions or MAPK activity; however, KCl-dependent contractions and MAPK activity were completely abolished by this procedure. An antibody specific for detecting caldesmon phosphorylated by MAPK, vs. protein kinase C (PKC), was developed and used to assess relative caldesmon phosphorylation in unstimulated and PDBu-stimulated muscle strips. In all cases investigated, the level of MAPK activity correlated with phosphocaldesmon immunoreactivity. Because arterial MAPK activity is regulated by PKC- and stretch-dependent mechanisms, these data are consistent with a role for MAPK and the subsequent phosphorylation of caldesmon as mediators in the stretch activation of vascular smooth muscle.

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