One of the unanswered questions in muscle hypertrophy is how new contractile units are inserted into a stable existing cytoskeletal meshwork. Regulation of actin capping by CapZ may play a role in remodeling processes, therefore, CapZ dynamics are determined during rapid growth of cardic cells in vitro. Neonatal rat ventricular myocytes were infected with adenovirus expressing green fluorescent protein-CapZ 1 and responded normally to hypertrophic stimuli. CapZ dynamics were analyzed by fluorescence recovery after photobleaching in cultured myocytes treated with endothelin-1 (100nM) or phenylephrine (10µM). Recovery by 30 sec was greater with endothelin treatment. Analysis 30 min postbleach showed CapZ infected cells treated with endothelin recovered more completely than controls (77 ± 9% vs. 50 ± 6%, p<0.001). Similar results were found with phenylephrine (77 ± 5%, p<0.05). A potential mechanism for PIP2 mediation of increased CapZ exchange in endothelin and phenylephrine treated cells was tested. Phosphatidylinositol bisphosphate (PIP2) sequestration with neomycin (500µM) blocked both endothelin (43 ± 6%, p<0.001) and phenylephrine (36 ± 4%, p<0.001) mediated recovery. The protein kinase C (PKC) inhibitor chelerythrine chloride (10µM) also blocked endothelin (53 ± 10%, p<0.001) and phenylephrine (42 ± 3%, p<0.001) mediated recovery. This study demonstrates for the first time that endothelin and phenylephrine alter CapZ dynamics through PIP2 and PKC dependent pathways, which might destabilize the existing framework and permit sarcomeric remodelling to proceed.