Search

After the incorporation of the tracheal microsomal membrane into bilayer lipid membrane (BLM), a new single channel permeable for calcium was observed. Using the BLM conditions, 53 mM Ca2+ in trans solution versus 200 nM Ca2+ in cis solution, the single calcium channel current at 0 mV was 1.4-2.1 pA and conductance was 62-75 pS. The channel Ca2+/K+ permeability ratio was 4.8. The open probability (P-open) was in the range of 0.7-0.97. The P-open, measured at -10 mV to +30 mV (trans-cis), was not voltage dependent. The channel was neither inhibited by 10-20 microM ruthenium red, a specific blocker of ryanodine calcium release channel, nor by 10-50 microM heparin, a specific blocker of IP3 receptor calcium release channel, and its activity was not influenced by addition of 0.1 mM MgATP. We suggest that the observed new channel is permeable for calcium, and it is neither identical with the known type 1 or 2 ryanodine calcium release channel, nor type 1 or 2 IP3 receptor calcium release channel.

Background Kidney fibrosis is frequently observed in cardiorenal diseases. Cyclic guanosine monophosphate (cGMP) serves as the most important second messenger of nitric oxide (NO) and has shown antifibrotic effects at enhanced levels in several experimental models of kidney diseases. Antifibrotic effects of cGMP signalling via cGMP-dependent protein kinases (cGK), in particular cGKI, have already been shown. Serelaxin and zaprinast are both able to increase cGMP signalling via influencing two independent pharmacological targets. Serelaxin is currently in phase III development for acute heart failure and has shown antifibrotic properties in several in vitro and in vivo experiments. It is discussed that serelaxin inhibits TGF-b signalling via RXFP1 receptor. Involvement of NO / cGMP in this process has also been revealed. Zaprinast is a selective inhibitor of phosphodiesterase V, which leads to enhanced levels of cGMP by blocking cGMP degradation.

Noise-induced hearing loss (NIHL) is a prevalent problem in the industrialized world. Now, Lukas Ruttiger and colleagues show that the phosphodiesterase inhibitor vardenafil can prevent NIHL in rats and mice. Noise-induced hearing loss (NIHL) is a global health hazard with considerable pathophysiological and social consequences that has no effective treatment. In the heart, lung and other organs, cyclic guanosine monophosphate (cGMP) facilitates protective processes in response to traumatic events. We therefore analyzed NIHL in mice with a genetic deletion of the gene encoding cGMP-dependent protein kinase type I (Prkg1) and found a greater vulnerability to and markedly less recovery from NIHL in these mice as compared to mice without the deletion. Prkg1 was expressed in the sensory cells and neurons of the inner ear of wild-type mice, and its expression partly overlapped with the expression profile of cGMP-hydrolyzing phosphodiesterase 5 (Pde5). Treatment of rats and wild-type mice with the Pde5 inhibitor vardenafil almost completely prevented NIHL and caused a Prkg1-dependent upregulation of poly (ADP-ribose) in hair cells and the spiral ganglion, suggesting an endogenous protective cGMP-Prkg1 signaling pathway that culminates in the activation of poly (ADP-ribose) polymerase. These data suggest vardenafil or related drugs as possible candidates for the treatment of NIHL.

Atrial natriuretic peptide (ANP), via its cGMP-forming guanylyl cyclase-A (GC-A) receptor, is critically involved in the regulation of arterial blood pressure and intravascular volume. To elucidate the role of the endothelial effects of ANP, we generated mice with conditional, endothelium (EC)-restricted ablation of the GC-A gene. Our observations in these and control mice demonstrated that ANP, via GC-A, mildly stimulates systemic transendothelial albumin transport in the microvasculature of skeletal muscle and skin. These and other studies indicate that concerted renal diuretic/natriuretic and mild endothelial hyperpermeability actions of ANP are essential to adjust intravascular fluid volume. However, this notion apparently contradicts published in vitro and in vivo studies showing that ANP can strenghen the pulmonary barrier under inflammatory conditions, suggesting that the hormone either acts differently on pulmonary vs systemic endothelium, or it exerts opposite effects on quiescent endothelia (enhanced permeability) and an inflammation-activated endothelium (barrier stabilization). Endothelial hyperpermeability is characteristic of many systemic diseases, such as allergic responses, edema, and sepsis. In particular, histamine markedly and acutely enhances endothelial permeability. Activation of endothelial Gq-coupled H1 receptors activates phospholipase C and elevates intracellular [Ca2+], ultimately leading to actin-myosin contraction and paracellular leakiness. Here we combined studies in microvascular endothelial cells and intravital microscopy of vascular permeability in the m. cremaster microcirculation to study whether ANP counteracts not only pulmonary but also systemic inflammation, i.e. histamine-induced hyperpermeability. Our observations reveal that transient receptor potential canonical (TRPC) 6 channels mediate the inflammatory effects of histamine. Most importantly, they characterize a regulatory pathway by which histamine-induced activation of TRPC6 channels and subsequent calcium-dependent acute endothelial hyperpermeability are prevented by ANP/GC-A-induced, cGMP-dependent protein kinase I (cGKI) - mediated inhibitory phosphorylation of these channels.

The cGMP-dependent protein kinase type I (cGKI) is involved in the modulation of neuronal plasticity and learning in the hippocampus and cerebellum. The expression and potential function of cGKI and its isoforms, cGKIα and cGKIβ in other brain regions is not completely resolved. We immunohistochemical study to elucidate the distribution of cGKI protein in the CNS and eye of the mouse. The specificity of the cGKI antibody was controlled by using tissue sections of cGKI knockout mice. Expression of cGKI protein was confirmed in cerebellar Purkinje cells, hippocampus, and dorsomedial hypothalamus. However, we also detected a number of additional cGKI-positive regions, e.g. deep cerebellar nuclei, cerebral cortex, subcommissural organ, various hypothalamic regions, olfactory bulb, pituitary gland, and retina. Immunostaining with isoform-specific antibodies indicated that the cGKIα isoform is prominent in the cerebellum and medulla, whereas cGKIβ is predominant in the cortex, hippocampus, hypothalamus, and olfactory bulb. These results suggest that the distribution and potential function of cGKI in the mammalian brain is broader than previously reported. from 2nd International Conference of cGMP Generators, Effectors and Therapeutic Implications Potsdam, Germany, 10–12 June, 2005

Signaling by NO/cGMP relaxes various smooth muscles, modulating thereby vascular tone and gastrointestinal motility. An important signaling pathway of cGMPdependent protein kinase type I (cGKI)-dependent relaxation is mediated by IRAG (IP3 Receptor Associated cGKI substrate) which is highly expressed in smooth muscle tissues. In order to elucidate the physiological role of IRAG we generated IRAG knockout mice by targeted deletion of exon 3.

Cyclic guanosine monophosphate (cGMP) is synthesized by nitric oxide or natriuretic peptide–stimulated guanylyl cyclases and exhibits pleiotropic regulatory functions in the kidney. Hence, integration of cGMP signaling by cGMP-dependent protein kinases (cGKs) might play a critical role in renal physiology; however, detailed renal localization of cGKs is still lacking. Here, we performed an immunohistochemical analysis of cGKIα and cGKIβ isozymes in the mouse kidney and found both in arterioles, the mesangium, and within the cortical interstitium. In contrast to cGKIα, the β-isoform was not detected in the juxtaglomerular apparatus or medullary fibroblasts. Since interstitial fibroblasts play a prominent role in interstitial fibrosis, we focused our study on cGKI function in the interstitium, emphasizing a functional differentiation of both isoforms, and determined whether cGKIs influence renal fibrosis induced by unilateral ureter obstruction. Treatment with the guanylyl cyclase activators YC1 or isosorbide dinitrate showed stronger antifibrotic effects in wild-type than in cGKI-knockout or in smooth muscle-cGKIα-rescue mice, which are cGKI deficient in the kidney except in the renal vasculature. Moreover, fibrosis influenced the mRNA and protein expression levels of cGKIα more strongly than cGKIβ. Thus, our results indicate that cGMP, acting primarily through cGKIα, is an important suppressor of kidney fibrosis.