My research program focuses on investigating the molecular mechanism governing contractility in smooth and cardiac muscle. The laboratory uses technically demanding, state-of-the-art mechanical, molecular, biochemical and transgenic techniques.

One project focuses on the molecular determinants for the kinetics of the actomyosin ATPase and force maintenance in smooth muscle. We have demonstrated that the kinetic cycle for slow, or tonic smooth muscle has two additional steps; an attached, low force producing ADPPi bound state and a nucleotide free force producing state. The additional rigor state can explain the larger angular motion of the attached cross-bridge during its power stroke in smooth muscle compared to striated muscle. Further, the group has demonstrated that a seven amino acid insert in the smooth muscle myosin head is responsible for these additional states. More recently, we have begun investigating the role of nonmuscle myosin II in defining the tonic contractile phenotype.

Another major project is focused on nitric oxide signaling in smooth muscle. Myosin light chain phosphatase is a trimeric enzyme with a catalytic subunit, a targeting subunit (MYPT1) and a subunit of unknown function. Alternative splicing of two different exons produces four MYPT1 isoforms, and isoform expression is developmentally regulated and tissue specific. We have demonstrated that alternative splicing of a 3? exon produces leucine zipper positive and negative MYPT1 isoforms. More importantly, the leucine zipper is required for protein kinase G mediated activation of the enzyme and the sensitivity to cGMP (or nitric oxide) mediated smooth muscle relaxation is regulated by relative leucine zipper +/- MYPT1 expression. Currently, we are focused on determining how the leucine zipper regulates cGMP mediated activation of the phosphatase.

We are also interested in the contribution of MYPT1 isoform expression to the vascular abnormalities associated with congestive heart failure (CHF). We have demonstrated in an animal model of HF that the relative expression of leucine zipper positive MYPT1 isoforms is down regulated, and the decrease in leucine zipper positive MYPT1 expression contributes to the molecular mechanism of both the decrease in sensitivity to nitric oxide mediated vasodilatation and the resting vasoconstriction associated with this clinical syndrome. Additionally, recent work shows that ACE-inhibitor therapy prevents the decrease in leucine zipper MYPT1 isoform expression and this could explain some of the beneficial effects of ACE-inhibitor therapy over other vasodilators in the treatment of CHF. We are currently focusing on the genes differentially regulated by ACE-inhibitor therapy in an effort to uncover markers of the response to therapy and/or disease progression.