No abstract

cGMP-dependent protein kinases (cGK) are serine/threonine kinases that are widely distributed in eukaryotes. Two genes--prkg1 and prkg2--code for cGKs, namely cGKI and cGKII. In mammals, two isozymes, cGKIalpha and cGKIbeta, are generated from the prkg1 gene. The cGKI isozymes are prominent in all types of smooth muscle, platelets, and specific neuronal areas such as cerebellar Purkinje cells, hippocampal neurons, and the lateral amygdala. The cGKII prevails in the secretory epithelium of the small intestine, the juxta-glomerular cells, the adrenal cortex, the chondrocytes, and in the nucleus suprachiasmaticus. Both cGKs are major downstream effectors of many, but not all signalling events of the NO/cGMP and the ANP/cGMP pathways. cGKI relaxes smooth muscle tone and prevents platelet aggregation, whereas cGKII inhibits renin secretion, chloride/water secretion in the small intestine, the resetting of the clock during early night, and endochondreal bone growth. cGKs are also modulators of cell growth and many other functions.

Lack of CMBK channels renders the heart more susceptible to ischemia/reperfusion injury, whereas the pathological events elicited by ischemia/reperfusion do not involve BK in vascular smooth muscle cells. BK seems to permit the protective effects triggered by cinaciguat, riociguat, and different phosphodiesterase-5 inhibitors and beneficial actions of ischemic preconditioning and ischemic postconditioning by a mechanism stemming primarily from cardiomyocytes. This study establishes mitochondrial CMBK channels as a promising target for limiting acute cardiac damage and adverse long-term events that occur after myocardial infarction.

It has been suggested that cGMP kinase I (cGKI) dampens cardiac hypertrophy. We have compared the effect of isoproterenol (ISO) and transverse aortic constriction (TAC) on hypertrophy in WT [control (CTR)] mice, total cGKI-KO mice, and cGKIβ rescue mice (βRM) lacking cGKI specifically in cardiomyocytes (CMs). Infusion of ISO did not change the expression of cGKI in the hearts of CTR mice or βRM but raised the heart weight by ∼20% in both. An identical hypertrophic growth response was measured in CMs from CTR mice and βRM and in isolated adult CMs cultured with or without 1 μM ISO. In both genotypes, ISO infusion induced similar changes in the expression of hypertrophy-associated cardiac genes and significant elevation of serum atrial natriuretic peptide and total cardiac cGMP. No differences in cardiac hypertrophy were obtained by 7-day ISO infusion in 4-to 6-week-old conventional cGKI-KO and CTR mice. Furthermore, TAC-induced hypertrophy of CTR mice and βRM was not different and did not result in changes of the cGMP-hydrolyzing phosphodiesterase activities in hypertropic hearts or CMs. These results strongly suggest that cardiac myocyte cGKI does not affect the development of heart hypertrophy induced by pressure overload or chronic ISO infusion.cyclic nucleotides | phosphodiesterase | phosphorylation | transverse aortic constriction | sildenafil C linical studies and genetically modified mice have supported the notion that natriuretic peptides (NPs), the particulate guanylyl cyclase (GC)-A, and the second messenger cGMP can attenuate the development of pressure-or volume-induced cardiac hypertrophy and fibrosis (1). Disruption of the murine GC-A gene, the receptor for the cardiac "hormones" atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), results in salt-resistant elevation of blood pressure, cardiac fibrosis, and hypertrophy (2, 3). To a great extent, hypertrophy is independent of blood pressure elevation (4, 5) but is enhanced transverse aortic constriction (TAC) in the absence of GC-A (4). Further studies using cardiac muscle-specific deletion of GC-A confirmed that cardiac muscle hypertrophy is independent of changes in blood pressure (6). ANP, nitric oxide (NO) donors, and 8-Br-cGMP inhibited norepinephrine-induced hypertrophy of cardiac cells and fibroblasts (7,8).Although it is recognized that GC-A-deficient hearts exhibit marked hypertrophy with interstitial fibrosis (2, 9), deletion of ANP did not result in obvious hypertrophy and fibrosis (10). Other reports have indicated that ANP ablation in mice causes an accelerated susceptibility to hypertrophy induced by different stress stimuli (11,12). Obviously, ANP and BNP secreted by the cardiomyocytes (CMs) act as paracrine factors that exert antifibrotic effects in vivo and play a role as local regulators of ventricular remodeling. Furthermore, it has been shown that rats expressing a dominant-negative mutant of GC-B and having an attenuated cGMP response to C-natriuretic peptide and a normal response to ANP showed marked cardiac hyp...