Phosphodiesterase 8A (PDE8A) regulates excitation-contraction coupling in ventricular myocytes.

In ventricular myocytes, activation of protein kinase A (PKA) by 3'-5' cyclic adenosine monophosphate (cAMP) increases the force of contraction by increasing L-type Ca(2+) channel currents (I(Ca)) and sarcoplasmic reticulum (SR) Ca(2+) release during excitation-contraction coupling. Cyclic-nucleotide phosphodiesterases (PDEs) comprise a large family of enzymes whose role in the cell is to regulate the spatial and temporal profile of cAMP signals by controlling the degradation of this second messenger. At present, however, the molecular identity and functional roles of the PDEs expressed in ventricular myocytes are incompletely understood. Here, we tested the hypothesis that PDE8A plays a critical role in the modulation of at least one compartment of cAMP and hence PKA activity during beta-adrenergic receptor (betaAR) activation in ventricular myocytes. Consistent with this hypothesis, we found that PDE8A transcript and protein are expressed in ventricular myocytes. Our data indicate that evoked [Ca(2+)](i) transients and I(Ca) increased to a much larger extent in PDE8A null (PDE8A(-/-)) than in wild-type (WT) myocytes during beta-adrenergic signaling activation. In addition, Ca(2+) spark activity was higher in PDE8A(-/-) than in WT myocytes. Our data indicate that PDE8A is a novel cardiac PDE that controls one or more pools of cAMP implicated in regulation of Ca(2+) movement through cardiomyocyte.

Analysis of ankyrin-B gene mutations in patients with long QT syndrome / 南方医科大学学报

<p><b>OBJECTIVE</b>To identify the ankyrin-B gene mutations that cause long QT syndrome (LQTS) and determine the prevalence of such mutations in Japanese patients with LQTS.</p><p><b>METHODS</b>We conducted a search for ankyrin-B gene mutation in 78 unrelated patients with LQTS (28 males and 50 females, aged 2 to 89 years). With informed consent from all the subjects and/or their parents, genomic DNA was purified from the white blood cells of the patients and amplified using polymerase chain reaction (PCR). Single-strand conformational polymorphism (SSCP) analysis of the amplified DNA was performed to screen for mutations and aberrant SSCP products were isolated and sequenced by dye terminator cycle sequencing method using an automated fluorescent sequencer. PCR and restriction fragment length polymorphism (PCR-RFLP) analysis was carried out to further confirm the missense mutations by comparison with samples from 150 normal healthy individuals.</p><p><b>RESULTS</b>We identified a T to A transition mutation at position 4,603 in exon 40, resulting in the substitution of arginine for a tryptophan at amino acid residue 1,535 (W1535R) in the regulatory domain of 220-kD ankyrin-B, which is a highly conserved domain shared by different species.</p><p><b>CONCLUSION</b>This novel missense mutation in the ankyrin-B gene may be a cause of type 4 LQTS. Ankyrin-B gene mutation might not play the major role in LQTS in Japanese.</p>