Variable Effects of Phorbol Dibutyrate, Blebbistatin, and Nifedipine on Force Production in Rabbit Femoral and Saphenous Arteries

Hana Poser
Marquette University
Mentor: Dr. Thomas Eddinger

This study examines the effects of various pharmacological agents on force production in vascular smooth muscle arteries.  Mechanical measurements were taken on an isometric force transducer after sections of rabbit femoral and saphenous arteries were cleaned and hung.  The secondary protein kinase C (PKC) pathway was examined through stimulation of PKC with agonist phorbol dibutyrate 10-7 M (PDBu). Tissues were also treated with prepared solutions of antagonist blebbistatin 3 x 10-6 M and Ca+2 channel blocker nifedipine 10-6 M.  Smooth muscle is responsible for contraction of hollow organs including the bladder, stomach, uterus, arteries, and veins.  Contractile force in smooth muscle is regulated through the phosphorylation of myosin light chain 20 (MLC20), which causes contraction, followed by the dephosphorylation of MLC20, which leads to relaxation.  The main contractile pathway is through the influx and efflux of Ca+2, but there are other secondary pathways by which myosin can become phosphorylated and dephosphorylated though the activation and deactivation of various regulatory proteins.  The rabbit femoral and saphenous arteries have similar function, but respond differently to K+ stimulation.  The femoral artery produces a tonic response while the saphenous artery exhibits a phasic response to K+ activation.  The reason for these differences is unknown.  PDBu 10-7 M stimulation increased peak force in the femoral artery while decreasing peak force in the saphenous artery compared to K+ stimulated peak force.  The femoral artery reached its peak force within 10 min. whereas the saphenous artery took closer to 2 hrs to reach peak with PDBu 10-7 M addition.  Our results show variation in the PKC pathway between the femoral and saphenous arteries.   The data also contradicts published data suggesting PDBu works via a Ca+2 independent pathway.
 
 

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