Calponin-1 is a 34 kDa actin-binding protein with regions of sequence homology to cardiac troponin I and T. It is located in the cytoskeleton and contractile apparatus of differentiated smooth muscle cells. There are 3 isoforms of calponin: calponin-1 (h1 or basic), calponin-2 (h2 or neutral), and calponin-3 (h3 or acidic). Calponin-1 is implicated in the regulation of smooth muscle contraction by mediating intracellular signaling responses to some vasoconstrictors by acting as a contractile scaffold protein. This mechanism is based on results in aortic smooth muscle cells stimulated with phenylephrine, which showed calponin-1 connecting protein kinase C and ERK1/2 pathways to promote contractility.