8-bromocyclic-gmp and calmidazolium

Natriuretic peptides (NPs) may work as neuromodulators through their associated receptors [NP receptors (NPRs)]. By immunocytochemistry, we showed that NPR-A and NPR-B were expressed abundantly on both ON-type and OFF-type bipolar cells (BCs) in rat retina, including the dendrites, somata, and axon terminals. Whole-cell recordings made from isolated ON-type BCs further showed that brain natriuretic peptide (BNP) suppressed GABAA receptor-, but not GABAC receptor-, mediated currents of the BCs, which was blocked by the NPR-A antagonist anantin. The NPR-C agonist c-ANF [des(Gln18, Ser19, Gln20, Leu21, Gly22)ANF(4-23)-NH2] did not suppress GABAA currents. The BNP effect on GABAA currents was abolished with preincubation with the pGC-A/B antagonist HS-142-1 but mimicked by application of 8-bromoguanosine-3',5'-cyclomonophosphate. These results suggest that elevated levels of intracellular cGMP caused by activation of NPR-A may mediate the BNP effect. Internal infusion of the cGMP-dependent protein kinase G (PKG) inhibitor KT5823 essentially blocked the BNP-induced reduction of GABAA currents. Moreover, calcium imaging showed that BNP caused a significant elevation of intracellular calcium that could be caused by increased calcium release from intracellular stores by PKG. The BNP effect was blocked by the ryanodine receptor modulators caffeine, ryanodine, and ruthenium red but not by the IP3 receptor antagonists heparin and xestospongin-C. Furthermore, the BNP effect was abolished after application of the blocker of endoplasmic reticulum Ca2+-ATPase thapsigargin and greatly reduced by the calmodulin inhibitors W-7 and calmidazolium. We therefore conclude that the increased calcium release from ryanodine-sensitive calcium stores by BNP may be responsible for the BNP-caused GABAA response suppression in ON-type BCs through stimulating calmodulin.

Topics: Animals; Atrial Natriuretic Factor; Caffeine; Calcium; Calcium Channels; Calcium Signaling; Calcium-Transporting ATPases; Calmodulin; Carbazoles; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; GABA-A Receptor Antagonists; gamma-Aminobutyric Acid; Guanylate Cyclase; Heparin; Imidazoles; Indoles; Inositol 1,4,5-Trisphosphate Receptors; Macrocyclic Compounds; Male; Membrane Potentials; Natriuretic Peptide, Brain; Oxazoles; Patch-Clamp Techniques; Peptide Fragments; Peptides, Cyclic; Polysaccharides; Protein Kinase Inhibitors; Rats; Rats, Sprague-Dawley; Receptors, Atrial Natriuretic Factor; Receptors, Cytoplasmic and Nuclear; Receptors, GABA; Receptors, GABA-A; Retinal Bipolar Cells; Ruthenium Red; Ryanodine; Ryanodine Receptor Calcium Release Channel; Thapsigargin

In this study we have investigated the role of oxygen delivery and of classic second messengers on erythropoietin production by the isolated perfused rat kidney. We found that the rat kidney was capable of de novo synthesis of erythropoietin. The erythropoietin production rate was inversely related to the oxygen pressure in the perfusate and increased from 0.17 to 1.85 U erythropoietin h-1 g kidney-1 when arterial PO2 was lowered from 500 mmHg to 30 mmHg. Addition of forskolin (10 microM) and 8-bromo-cGMP (100 microM) to the perfusate elicited significant effects on the renal vascular resistance, but had no significant effect on erythropoietin production. Hypoxia-induced erythropoietin formation, however, was blocked by calmidazolium (1 microM) and W-7 (10 microM), two structurally different putative calmodulin antagonists. Calmidazolium and W-7 had no effect on other functional parameters of the isolated perfused rat kidney such as flow rate, glomerular filtration rate or sodium reabsorption. Our findings suggest that the oxygen-sensing mechanism that controls renal erythropoietin production is primarily located in the kidney itself. A calcium/calmodulin-dependent cellular reaction could be involved in the signal transduction process.

Topics: Animals; Calmodulin; Colforsin; Cyclic GMP; Erythropoietin; Imidazoles; Kidney; Kinetics; Male; Oxygen; Rats; Second Messenger Systems; Sulfonamides; Vascular Resistance

The effects of calmidazolium, carbachol and membrane permeable derivatives of cGMP (dipalmitoyl cGMP and 8-Bromo cGMP) on the longitudinal internal resistivity (Ri) were studied in the rabbit atrial trabeculae by means of electrophysiological recording techniques and histological planimetry. Calmidazolium as well as carbachol decreased Ri whereas cGMP-derivatives enhanced this resistivity. The effect of calmidazolium suggested that calmodulin reduced the cell coupling under control conditions. Carbachol decreased the Ca-inward current, and probably it prevented the calmodulin activation. The action of the nucleotides showed that cGMP did not mediate the cholinergic effect on the cell coupling. The possible interaction between calmodulin and cGMP was discussed.

Topics: Animals; Carbachol; Cyclic GMP; Electric Stimulation; Heart; Imidazoles; In Vitro Techniques; Myocardium; Palmitates; Rabbits

The pharmacological and biochemical mechanisms of contractile responses to the protein kinase C (PKC) activator phorbol-12,13-diacetate (PDA) were investigated in canine basilar arteries. In the normal medium, PDA elicited a strong, dose-related, and slow-developing sustained contraction. Among the constrictors examined, including serotonin, prostaglandin F2 alpha, and endothelin, only PDA yielded contractions in a Ca2(+)-free medium. In both media, the PDA-induced contractions were virtually inhibited by either staurosporine, H-7, or quinacrine, while neither neurotransmitter blockades nor R24571 (calmidazolium) exerted significant effects. In addition, it was shown that 8-bromocyclic GMP, but not 8-bromocyclic AMP, markedly curtailed the PDA-induced contractions. Biochemical analysis, furthermore, showed that PDA induced increased phosphorylations of 27- and 96-kDa and proteins other than the myosin light chain (MLC) 20-kDa protein. Thus, the present results open up a novel mechanism of sustained cerebral artery contractions, where PKC activation rather than Ca2+/calmodulin/MLC system plays a key role that is regulated both by phospholipase A2 and by cyclic GMP.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Alkaloids; Animals; Basilar Artery; Cyclic GMP; Dinoprost; Dogs; Endothelins; Enzyme Activation; Female; Imidazoles; Isoquinolines; Male; Muscle Contraction; Phorbol Esters; Phosphorylation; Piperazines; Protein Kinase C; Quinacrine; Serotonin; Staurosporine