CapZ dynamics are altered by endothelin-1 and phenylephrine via PIP2-and PKC-dependent mechanisms

Hartman TJ, Martin JL, Solaro RJ, Samarel AM, Russell B. CapZ dynamics are altered by endothelin-1 and phenylephrine via PIP2 and PKC-dependent mechanisms. Am J Physiol Cell Physiol 296: C1034-C1039, 2009. First published March 18, 2009; doi:10.1152/ajpcell.00544.2008.-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 cardiac cells in vitro. Neonatal rat ventricular myocytes were infected with adenovirus expressing green fluorescent protein-CapZ beta 1 and responded normally to hypertrophic stimuli. CapZ dynamics were analyzed by fluorescence recovery after photobleaching in cultured myocytes treated with endothelin-1 (100 nM) or phenylephrine (10 mu M). Recovery by 30 s 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 phosphatidylinositol bisphosphate (PIP2) mediation of increased CapZ exchange in endothelin-and phenylephrine-treated cells was tested. PIP2 sequestration with neomycin (500 mu M) blocked both endothelin-(43 +/- 6%, P < 0.001) and phenylephrine (36 +/- 4%, P < 0.001)-mediated recovery. The protein kinase C inhibitor chelerythrine chloride (10 mu M) 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.