Abstract
Protein kinase D (PKD) targets several proteins in the heart, including cardiac troponin I (cTnI) and class II histone deacetylases, and regulates cardiac contraction and hypertrophy. In adult rat ventricular myocytes (ARVM), PKD activation by endothelin-1 (ET1) occurs via protein kinase Cε and is attenuated by cAMP-dependent protein kinase (PKA). Intracellular compartmentalisation of cAMP, arising from localised activity of distinct cyclic nucleotide phosphodiesterase (PDE) isoforms, may result in spatially constrained regulation of the PKA activity that inhibits PKD activation. We have investigated the roles of the predominant cardiac PDE isoforms, PDE2, PDE3 and PDE4, in PKA-mediated inhibition of PKD activation. Pretreatment of ARVM with the non-selective PDE inhibitor isobutylmethylxanthine (IBMX) attenuated subsequent PKD activation by ET1. However, selective inhibition of PDE2 [by erythro-9-(2-hydroxy-3-nonyl) adenine, EHNA], PDE3 (by cilostamide) or PDE4 (by rolipram) individually had no effect on ET1-induced PKD activation. Selective inhibition of individual PDE isoforms also had no effect on the phosphorylation status of the established cardiac PKA substrates phospholamban (PLB; at Ser16) and cTnI (at Ser22/23), which increased markedly with IBMX. Combined administration of cilostamide and rolipram, like IBMX alone, attenuated ET1-induced PKD activation and increased PLB and cTnI phosphorylation, while combined administration of EHNA and cilostamide or EHNA and rolipram was ineffective. Thus, cAMP pools controlled by PDE3 and PDE4, but not PDE2, regulate the PKA activity that inhibits ET1-induced PKD activation. Furthermore, PDE3 and PDE4 play redundant roles in this process, such that inhibition of both isoforms is required to achieve PKA-mediated attenuation of PKD activation.