Phenotypic modifications of vascular smooth muscle cells could be responsible for vascular hyporeactivity to contracting agent in mechanically injured rat carotid artery

Abstract 

Vascular smooth muscle cells (VSMCs) that accumulate in neointima after angioplastic injury show different phenotypic characteristics from those of medial layer and an impaired reactivity to contracting agents. The aim of the study was to correlate the vascular hyporesponsiveness to the changes in intracellular calcium concentration [Ca²⁺]_i and the expression of proteins necessary for its utilization in mechanically injured rat carotid arteries (IC) at 14 and 28 days after angioplastic balloon. IC showed a significant reduction (P<0.01) to PE- or KCl-induced contraction as compared to uninjured carotid (UC). Fura-2AM-loaded VSMCs isolated from IC revealed that this hyporeactivity to PE or KCl was accompanied by the impairment of the increase in [Ca²⁺]_i induced by contracting agents in both Ca²⁺-free or -containing medium. Similar results were observed following the ryanodine challenge in VSMC. Western blot analysis showed a significant (P<0.05) reduction in myosin heavy chain (MHC) and IP₃-type III receptor expression in IC isolated at 14 days from injury compared to UC, while an improvement of these proteins expression was observed at 28 days after damage. On the other hand, in IC tissue, SERCA2 and α-actin expression, compared to UC was significantly higher at 14 days than at 28 days.

These data indicate that vascular hyporeactivity induced by mechanical injury may be due to alterations of either [Ca²⁺]_i or contractile proteins. These modifications could be related to the changes of VSMC phenotypic characteristics, as supported by the observed modifications in MHC, SERCA2 and α-actin expression, proteins considered as biological markers of cellular differentiation.

Keywords: Vascular hyporeactivity, Angioplastic balloon, Vascular smooth muscle cell phenotypic modification, Ca²⁺ flux