United Nations Environment Programme Capacity Building Pilot Project--training and interlaboratory study on persistent organic pollutant analysis under the Stockholm Convention.

Within the framework of a United Nations Environment Programme (UNEP) Capacity Building Project for training of laboratory staff in developing countries on persistent organic pollutant (POP) analysis, an interlaboratory study was organised following an initial evaluation of the performance of laboratories (reality check) and a series of training sessions. The target compounds were polychlorinated biphenyls (PCB) and organochlorine pesticides (OCP). Seven laboratories from five countries (Ecuador, Uruguay, Kenya, Moldova, and Fiji) participated. Most of the laboratories had no experience in determining PCBs. Although chromatograms improved considerably after the training and installation of new gas chromatographic (GC) columns at participating laboratories, the level of performance in the interlaboratory study was essentially on par with the moderate performance level achieved by European POP laboratories in the 1980s. Only some individual results were within +/-20% of the target values. The relative standard deviations (R.S.D.s) in POP concentrations determined by laboratories in a sediment sample were >200% in a number of cases. The results for a certified herring sample were better with at least some R.S.D. values below 50% and most below 100%. Clean up was as one of the main sources of error. After inspection it was ascertained that training of laboratory staff and investments in simple consumables such as glassware and GC columns would help to improve the quality of the analysis more than major investments in expensive instrumentation. Creating an effective network of POP laboratories at different continents together with a series of interlaboratory studies and workshops is suggested to improve the measurements of POPs in these countries.

Distribution of organotin compounds in the bivalves of the Aegean Sea, Greece.

Five bivalve species--Mytilus galloprovinciallis (Mediterranean mussels), Venus gallina (stripped venus), Modiola barbatus L. (bearded horse mussels), Pecten jacobeus (scallops) and Callista chione (hard clams)--were collected from seven areas in Aegean Sea, Greece, between August 2001 and January 2003 and analyzed for organotins (OTs). The concentrations (as geometric means) found were 17.1 ng g-1 for tributyltin (TBT), 18.8 ng g-1 for dibutytltin (DBT), 7.8 ng g-1 for monobutyltin (MBT) and 13.0 ng g-1 for triphenyltin (TPhT) (wet weight), which are at similar or lower levels than those reported worldwide. Studying OTs distribution between different bivalve species, lower concentrations were observed in mediterranean mussels, possibly due to their growth in water column (grown on sea net pens in mussel farms), in contrast to the free-ranging species, collected from fishing grounds. Concentrations of the OTs in the examined bivalves varied seasonally.

Improved glucuronide hydrolysis in the determination of urinary 1-hydroxypyrene.

The efficiency of the glucuronide hydrolysis in the determination of urinary 1-hydroxypyrene was investigated as a function of the reaction conditions. A significant improvement could be obtained by increasing the enzyme concentration described in the literature.

Inhibition of L-type Cav1.2 Ca2+ channels by 2,(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) and 2-[1-(3-dimethyl-aminopropyl)-5-methoxyindol-3-yl]-3-(1H-indol-3-yl) maleimide (Go6983).

Phosphatidylinositol 3-kinase (PI3-K) is involved in physiological processes of cellular proliferation and inflammation and, as postulated recently, in the regulation of L-type Ca(2+) channels. The latter conclusion arose in part from the inhibitory action of the compound 2,(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), which has been established as a selective PI3-K inhibitor (IC(50) = 1.4 microM). Herein we show, however, that LY294002 and an inhibitor of protein kinase C (PKC), 2-[1-(3-dimethylaminopropyl)-5-methoxyindol-3-yl]-3-(1H-indol-3-yl) maleimide (Go6983), act as direct Ca(2+)-channel inhibitors, with IC(50) values of approximately 20 and 10 microM, respectively. Because both drugs are commonly used at concentrations of approximately 10 microM or higher, the interpretation of such experiments is questionable with respect to a regulatory action of PI3-K or PKC on L-type Ca(2+) channels.

Voltage-dependent effects of barnidipine in rat vascular smooth muscle.

The effects of the dihydropyridine nifedipine and its more lipophilic congener, barnidipine, were investigated in smooth muscle preparations from the rat in resting and depolarizing conditions. Both drugs relaxed precontracted aortic rings more potently in depolarizing conditions, barnidipine being more potent than nifedipine. Currents through Ca2+ channels in rat vascular smooth muscle cells (A7r5) and in isolated rat cardiomyocytes were reduced more potently by both drugs at a holding potential of -40 mV than at -80 mV. However, barnidipine and nifedipine were more effective in reducing the current in A7r5 cells than in cardiomyocytes. The IC(50) obtained in aortic rings and in A7r5 cells were similar for barnidipine but an order of magnitude different for nifedipine. The results show that, in depolarizing conditions, barnidipine was more effective than nifedipine. It is suggested that the higher potency of barnidipine acting in vascular smooth muscle is related to both a higher affinity to the inactivated state of vascular Ca2+ channels and to a more lipophilic property as compared with nifedipine.

Effects of nitric oxide donors on cardiac contractility in wild-type and myoglobin-deficient mice.

1. The effects of the nitric oxide (NO) donors S-nitroso-N-acetylpenicillamine (SNAP), sodium(Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolate (DEA-NONOate), and (Z)-1-[N-(2-Aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NONOate) on force of contraction (F(c)) were studied in atrial and ventricular muscle strips obtained from wild-type (WT) and myoglobin-deficient (myo(-/-)) mice. 2. SNAP slightly reduced F(c) in preparations from WT mice at concentrations above 100 microM; this effect was more pronounced in myo(-/-) mice. 3. DEA-NONOate reduced F(c) in preparations from myo(-/-) mice to a larger extent than those from WT mice. 4. DETA-NONOate reduced F(c) in preparations from myo(-/-) but not from WT mice. 5. Pre-incubation with an inhibitor of the soluble guanylyl cyclase (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one; 100 microM) prevented the effects of SNAP, DEA-NONOate and DETA-NONOate on F(c) in myo(-/-) mice. 6. It is suggested that, in physiological conditions, myoglobin acts as intracellular scavenger preventing NO from reaching its intracellular receptors in cardiomyocytes, whereas, in myoglobin-deficient conditions, NO is able to reduce contractility via activation of the soluble guanylyl cyclase/cyclic GMP pathway.

Increased cardiac alpha-1-adrenoceptor density in rats following treatment with amiodarone.

This study was undertaken to investigate the interaction between amiodarone and alpha-1-adrenoceptors in rat cardiac cells. The level (Bmax) and affinity (Kd) of alpha-1-adrenoceptors in heart cells were determined by [3H]prazosin radioligand binding following amiodarone treatment. In cultured intact cardiocytes treated for 48 h with 10 microM amiodarone, [3H]prazosin binding increased by 31% compared with the control cells (p<0.05). The increase was both dose and time dependent and was found to be specific because no significant change occurred in creatine kinase activity. Additionally, under the same conditions, an increase in [3H]prazosin binding to cultured cardiocyte cell membranes was also obtained. Oral gavage of amiodarone to rats for 8 d resulted in a 25% increase in [3H]prazosin binding to isolated ventricle membranes compared with control rats (p<0.05). We conclude that amiodarone treatment can increase the response to alpha-1-adrenoceptors agonist in the heart due to an increase in the density of alpha-1-adrenoceptors.

Differences in the nitric oxide/soluble guanylyl cyclase signalling pathway in the myocardium of neonatal and adult rats.

The effects of a nitric oxide-donor, S-nitroso-N-acetylpenicillamine, and a direct activator of soluble guanylyl cyclase, 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1), on force of contraction (F(c)) and L-type Ca(2+) currents (I(Ca(L))) were investigated in myocardial preparations from neonatal and adult rats. Since hearts from adult and neonatal animals contained 160 and 47 mg/100 g wet weight myoglobin, respectively, its possible interaction with both drugs was also investigated. Both S-nitroso-N-acetylpenicillamine (100 microM) and YC-1 (30 microM) were ineffective in myocardial preparations from adult rats but reduced the magnitude of I(Ca(L)) and F(c) in preparations from neonatal rats. The latter effects were antagonised by 1H-[1,2, 4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 50 microM) and attenuated by myoglobin (30-300 microM), which also attenuated the effects of both drugs on pre-contracted aortic rings. The differential effects of S-nitroso-N-acetylpenicillamine and YC-1 in the myocardium from adult and neonatal rats may result from developmental changes in the content of myoglobin and/or in the NO/soluble guanylyl cyclase signal pathway.

Voltage dependence of L-arginine transport by hCAT-2A and hCAT-2B expressed in oocytes from Xenopus laevis.

Membrane potential and currents were investigated with the two-electrode voltage-clamp technique in Xenopus laevis oocytes expressing hCAT-2A or hCAT-2B, the splice variants of the human cationic amino acid transporter hCAT-2. Both hCAT-2A- and hCAT-2B-expressing oocytes exhibited a negative extracellular L-arginine concentration ([L-Arg](o))-sensitive membrane potential, additive to the K(+) diffusion potential, when cells were incubated in Leibovitz medium (containing 1.45 mM L-Arg and 0.25 mM L-lysine). The two carrier proteins produced inward and outward currents, which were dependent on the L-Arg gradient and membrane potential. Ion substitution experiments showed that the hCAT-induced currents were independent of external Na(+), K(+), Ca(2+), or Mg(2+). The apparent Michaelis-Menten constant values at -60 mV, obtained from plots of L-Arg-induced currents against [L-Arg](o), were 0.97 and 0.13 mM in oocytes expressing hCAT-2A and hCAT-2B, respectively; maximal currents amounted to -194 +/- 8 and -84 +/- 2 nA, respectively. At saturating [L-Arg](o), the current-voltage relationships of hCAT-2A-expressing oocytes became steeper, yielding an additional conductance up to 2 microS/oocyte, whereas those of hCAT-2B-expressing oocytes were simply shifted to the right, resulting in voltage-independent difference currents. The distinct electrochemical properties of the two isoforms of hCAT-2 are assumed to contribute differentially to the membrane transport and the maintenance of cationic amino acids in various tissues.

Barnidipine block of L-type Ca(2+) channel currents in rat ventricular cardiomyocytes.

The effects of barnidipine and nifedipine on L-type Ca(2+) current (I(Ca(L))) were investigated in ventricular cardiomyocytes from rats. Both barnidipine and nifedipine reduced I(Ca(L)) in a concentration and voltage dependent manner; the EC(50) were 80 and 130 nM at a holding potential of -80 mV, respectively, and 18 and 6 nM at -40 mV, respectively. Both drugs induced a leftward shift of the steady-state inactivation curve of I(Ca(L)). Using a twin pulse protocol, the relationships between the amount of block of I(Ca(L)) by either drug, seen during the second pulse, and the length of the first pulse were described by monoexponential functions reflecting onset of block, dependent on drug concentration. The onset of block by barnidipine was three times faster than that by nifedipine. With both drugs, recovery of I(Ca(L)) was 50 times slower than under control conditions and described by monoexponential functions reflecting offset of block (independent of drug concentration). The offset of block with barnidipine was three times slower than that with nifedipine. The time constants of block and unblock of I(Ca(L)) by both drugs were used to calculate binding and unbinding and to predict their effects at two frequencies. It is suggested that barnidipine exhibits a higher affinity to the inactivated Ca(2+) channel state as compared to nifedipine.

Involvement of K(+) channels in the relaxant effects of YC-1 in vascular smooth muscle.

This study addresses the question whether K(+) channels are involved in the vasorelaxant effects of 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl-indazole (YC-1 ). In rat aorta, guinea pig aorta, and guinea pig a. carotis, YC-1 inhibited contractions induced by phenylephrine (3 microM) more potently than those induced by K(+)(48 mM). In rat aorta, tetraethylammonium (10 mM), charybdotoxin (0.2 microM), and iberiotoxin (0.1 microM), but not glibenclamide (10 microM), attenuated the relaxant effects of YC-1. In guinea pig a. carotis, YC-1 (30 microM) induced a hyperpolarisation which was antagonised by 1H-[1,2,4]oxadiazolo[4, 3-a]quinoxalin-1-one (ODQ; 50 microM). In rat aorta, YC-1 (30 microM) increased the rate constant of 86Rb-efflux. The effect of YC-1 was potentiated by zaprinast (10 microM), but inhibited by ODQ (50 microM) or charybdotoxin (0.2 microM). In smooth muscle cells from rat aorta, YC-1 (10 microM) increased BK(Ca) channel activity. It is suggested that YC-1-induced vasorelaxation is partially mediated by the activation of K(+) channels.

Failure of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) to inhibit soluble guanylyl cyclase in rat ventricular cardiomyocytes.

1. The effects of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), an inhibitor of soluble guanylyl cyclase (sGC), were investigated in aortic rings and ventricular cardiomyocytes from rats. The production of cyclic GMP was stimulated by NO.-donors or carbachol. Additionally, the effects of ODQ were studied in cytosolic extracts from both tissues in which the cyclic GMP production was stimulated by S-nitroso-N-acetylpenicillamine (SNAP). 2. In endothelium-intact aortic rings, SNAP (100 microM), 2,2'-(hydroxynitrosohydrazino)bis-ethana-mine (DETA NONOate; 100 microM), or carbachol (10 microM) increased cyclic GMP levels about 4 fold. These effects were abolished by ODQ (50 microM). 3. In cardiomyocytes, SNAP (100 microM), DETA NONOate (100 microM), or carbachol (10 microM) increased cyclic GMP levels about 2 fold. These effects were not affected by ODQ (50 microM). 4. In cytosolic extracts from aortic rings and cardiomyocytes, SNAP (100 microM) induced about 50 fold increases in cyclic GMP levels. ODQ (50 microM) reduced these effects by about 50%. 5. In extracts from cardiomyocytes, increases by SNAP (100 microM) of cyclic GMP levels were attenuated by myoglobin dependent on concentration: at 300 microM myoglobin, SNAP (100 microM) increased cyclic GMP levels only 3 fold. Inhibitory effects of ODQ (50 microM) were abolished by 300 microM myoglobin. 6. It is suggested that both NO. and ODQ can bind to myoglobin which, at high concentrations. can diminish their effects on sGC. Such a scavenger function of myoglobin could explain why NO. and ODQ exert only minor effects in cardiomyocytes (with high myoglobin content) but strong effects in aortic tissue (virtually devoid of myoglobin).

Inhibition by fendiline of the transient outward current in rat ventricular cardiomyocytes.

The effects of fendiline on the transient outward current (Ito) were investigated in rat ventricular cardiomyocytes. Extracellularly applied fendiline reduced peak and steady-state current amplitude of Ito; the inactivation of Ito was accelerated by the drug, which reflects onset of block. The described effects were concentration dependent: half-maximal effects were achieved at approximately 3 microM fendiline. Intracellularly applied fendiline (3 microM) did not affect Ito within 5 min. The steady-state current amplitude of Ito was more efficiently suppressed by the drug at 22 +/- 1 degrees C than at 36 +/- 1 degrees C. The recovery of Ito was analyzed by the application of twin depolarizing voltage pulses, interrupted by variable pulse intervals. In the presence of fendiline, recovery of Ito was about twofold slower than that under control conditions, independent of the drug concentration used, which reflects offset from block. Concentration-dependent onset but concentration-independent offset of block suggest that the described time constants correspond to voltage-dependent net binding and unbinding, respectively, of fendiline at its receptor sites. It is proposed that fendiline binds extracellularly at positive potentials to Ito channels in their open state and dissociates from the channels at rest.

Mechanism of block by 4-aminopyridine of the transient outward current in rat ventricular cardiomyocytes.

The effects of 4-aminopyridine (4-AP) on the transient outward current (I(to)) were investigated in rat ventricular cardiomyocytes at different values of intracellular pH (pHi) and extracellular pH (pHo). The 4-AP was administered either extracellularly (bath application) or intracellularly (diffusion from the intrapipette solution). The 4-AP diminished I(to) given either from inside or outside the cell membrane. The block by extracellularly applied 4-AP (4-APo) of the peak amplitude of I(to) was decreased by external acidification but increased by external alkalinization; conversely, the block by 4-APo was decreased by internal alkalinization but increased by internal acidification. Intracellularly applied 4-AP (3 mM) was more effective at low pHi. Because 4-AP is a tertiary amine and exists in protonated and unprotonated forms, these results are in agreement with the assumption that one major mechanism for 4-AP to block I(to) is to penetrate the cell membrane in its uncharged form and to reach intracellular binding sites in its protonated form.

Open state block by fendiline of L-type Ca++ channels in ventricular myocytes from rat heart.

The effects of fendiline on L-type Ca++ currents [ICa(L)] were investigated in rat ventricular cardiomyocytes using the patch-clamp technique both in the whole-cell disrupted-patch and in the cell-attached configuration. For comparison, the effects of verapamil were also investigated. Both compounds depressed the magnitude of whole cell ICa(L), verapamil being about 15 times more potent than fendiline. Verapamil did not change the time course of the current, whereas fendiline accelerated its decay when either Ca++ or Ba++ ions were used as charge carriers. In the presence of the Ca++ agonist BayK8644 (10 microM), the potency ratio of fendiline/verapamil was inverted. BayK8644 (10 microM) also reversed the potency ratio of verapamil/fendiline in smooth muscle, with respect to changes in tension induced by K+ (48 mM). In single channel recordings at 0.1 Hz, in the presence of BayK8644 (1 microM) and using Ba++ ions as the charge carrier, fendiline (1 microM) reduced mean open time by 34% and channel availability by 8%; the ensemble average current of Ca++ channels was reduced by 43%. In the same experimental conditions, verapamil (1 microM) was ineffective. These results can be explained by the assumption that fendiline blocks Ca++ channels preferentially in the open state, in contrast to verapamil which blocks preferentially inactivated Ca++ channels.

Second messenger-controlled membrane conductance in locust (Locusta migratoria) olfactory neurons.

The membrane conductance of olfactory neurons of Locusta migratoria was examined using the whole-cell configuration of the patch-clamp technique. Intracellular application of the second messenger inositol 1,4,5 trisphosphate (IP(3)) via a dual pipette technique elicited a clear increase in the membrane conductance. The IP(3)-induced conductance increased due to a rise in the extracellular concentration of calcium from 100&mgr;M to 4mM. Micromolar concentrations of ruthenium red partially blocked the IP(3)-induced increase in membrane conductance. Stimulating olfactory neurons with odour (hexenoic acid) resulted in an increase in the membrane conductance partially similar to that mediated IP(3). These findings suggest that stimulation with appropriate odours as well as intracellular application of IP(3) activate the same calcium-permeable ion channels in the plasma membrane of insect olfactory neurons.

Cardiac effects of isoliquiritigenin.

The effects of isoliquiritigenin on force of contraction (Fc), L-type Ca2+ current (I(Ca)) and intracellular Ca2+ concentration ([Ca2+]i) were investigated in rat ventricular heart muscle. Isoliquiritigenin increased Fc and I(Ca) and, after longer exposure times, resting tension and [Ca2+]i. The effect of isoliquiritigenin (100 microM) on I(Ca) was diminished by Rp-cAMPS (30 microM). 1H-[1,2,4]oxa- diazolo[4,3-a]quinoxalin-1-one (50 microM) did not influence the effects of isoliquiritigenin on Fc and I(Ca). The positive inotropic effects of isoprenaline and forskolin, but not of 3-isobutyl-1-methylxanthine, were potentiated by isoliquiritigenin (100 microM). In the presence of milrinone (10 microM), no further effects of isoliquiritigenin (100 microM) on Fc and I(Ca) were observed. It is suggested that the increase in Fc and I(Ca) by isoliquiritigenin is due to an accumulation of cyclic AMP. These effects are probably unrelated to an effect of the drug on soluble guanylyl cyclase, as reported for smooth muscle, but rather due to a direct inhibition of phosphodiesterase III activity.

Differential effects of isoliquiritigenin and YC-1 in rat aortic smooth muscle.

We investigated the effects of isoliquiritigenin and YC-1 (3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole) on tension in endothelial-free rat aortic rings precontracted with phenylephrine (3 microM). Both compounds induced a concentration-dependent relaxation (EC50 of YC-1 1.9 microM and of isoliquiritigenin 9.4 microM). The effects developed faster with YC-1 than with isoliquiritigenin, and the effects of YC-1 were potentiated by isoliquiritigenin (10 microM). 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (30 microM) inhibited the effect of YC-1, but not of isoliquiritigenin. These results suggest that the effects of YC-1 are due to stimulation of soluble guanylyl cyclase activity, whereas the effects of isoliquiritigenin are rather related to inhibition of phosphodiesterase activity.

Kinetics and state-dependent effects of verapamil on cardiac L-type calcium channels.

The voltage dependence and the kinetics of block by verapamil of L-type calcium current (ICa) were investigated in ventricular myocytes from rat hearts using the whole-cell patch-clamp technique. ICa was elicited repetitively in response to depolarizing voltage pulses from -80 mV to 0 mV at different pulse intervals and durations. Verapamil reduced the magnitude of ICa in a frequency-dependent manner without tonic component. The time course of ICa remained unchanged suggesting that not open but inactivated channels were affected by the drug. The interaction of verapamil with inactivated channels was investigated by the application of twin pulses. In the presence of verapamil, the duration of the first pulse significantly determined the magnitude of ICa during the second pulse. Variation of the duration of the first pulse between 12 and 3000 ms, followed by a pulse interval of 100 ms, resulted into a gradual decrease of ICa during the second pulse (180 ms), described by concentration-dependent monoexponential decay curves (tau = 1060 +/- 138 ms at 0.3 microM (n = 3); tau = 310 +/- 24 ms at 1 microM (n = 6), and tau = 125 +/- 7 ms at 10 microM (n = 5); means +/- SEM). Under control conditions, the changes in ICa were comparably negligible. The recovery of ICa from block was analyzed by the application of a twin pulse protocol in which two depolarising voltage pulses at fixed length (1. pulse at 3 s and 2. pulse at 180 ms) were interrupted by variable pulse intervals (6 ms-60 s). Under control conditions, recovery from inactivation was fast (tau = 11 +/- 0.7 ms; means +/- SEM; n = 3). In the presence of verapamil, recovery from block was about 500 times slower than under control conditions, independent of the drug concentration (tau = 5.05 +/- 0.44 s at 0.3 microM (n = 3), tau = 6.7 +/- 0.69 s at 1 microM (n = 4), and tau = 6.02 +/- 0.9 s at 10 microM (n = 5); means +/- SEM). Since development of block was dependent on the concentration of verapamil, whereas recovery from block was independent from the drug concentration, it is assumed that the described time constants for block and unblock reflect voltage-dependent net binding (tau on) and unbinding (tau off), respectively, of verapamil at its receptor sites. A computer simulation, including the time constants of block development at 0 mV and of recovery from block at -80 mV, predicted reasonably well the observed frequency-dependent block of ICa by verapamil. The development of either measured or calculated block of ICa, using 180 ms depolarising voltage pulses from -80 mV to 0 mV, was fitted by identical monoexponential association curves (tau = 7 s each at 0.2 Hz and tau = 1.7 s each at 1 Hz). When Ba2+ was used as the charge carrier, which removes the calcium-dependent inactivation of the current, verapamil (3 microM) was less efficient: ICa was decreased by 57 +/- 6% (means +/- SEM; n = 6), whereas IBa was decreased by 24 +/- 4% (means +/- SEM; n = 5). It is proposed that verapamil binds to calcium channels in their inactivated state at more positive potentials and dissociates from the channels in the resting state at more negative potentials. In the proposed scheme of periodical drug binding and unbinding, dependent on the state of the channels, the development of frequency-dependent block of ICa by verapamil is adequately predicted by the construction of cumulative association/ dissociation curves which include the experimentally determined time constants of development and recovery from block at 0 mV and -80 mV, respectively.

Activation of soluble guanylyl cyclase by YC-1 in aortic smooth muscle but not in ventricular myocardium from rat.

1. The effects of YC-1 (3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole), an activator of soluble guanylyl cyclase, on tension, levels of cyclic GMP and cyclic AMP, and cardiac L-type Ca2+-current (I[Ca(L)]) were investigated in aortic smooth muscle and ventricular heart muscle from rat. 2. YC-1 (0.1-30 microM) induced a concentration-dependent relaxation in aortic rings precontracted with phenylephrine (3 microM). The relaxant effects of YC-1 were reversed by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (30 microM; ODQ), potentiated by zaprinast (10 microM) and antagonized by Rp-8-Br-cGMPS (100 microM). 3. In ventricular heart muscle strips, YC-1 (30 microM) exhibited no effects on force of contraction (Fc) in the absence or presence of either zaprinast (10 microM) or 3-isobutyl-1-methylxanthine (30 microM). Fc was slightly increased by YC-1 (30 microM) in the presence of isoprenaline (100 nM), but this effect was not influenced by ODQ (30 microM). 4. Cardiac I[Ca(L)] was not significantly affected by YC-1 (30 microM), either in the absence or presence of isoprenaline (30 nM). 5. In aortic rings, cyclic GMP levels were increased almost 3 fold by YC-1 (30 microM); this effect was abolished by ODQ (30 microM). In isolated ventricular cardiomyocytes, cyclic GMP levels were not affected by YC-1 (30 microM) but almost doubled by activation of particular guanylyl cyclase with atriopeptin II (100 nM). 6. YC-1 (30 microM) did not increase cyclic AMP levels either in aortic rings or in ventricular cardiomyocytes. In contrast, isoprenaline (3 microM) increased cyclic AMP levels about two fold in both tissues. In cardiomyocytes, the effect of isoprenaline (3 microM) was slightly enhanced by YC-1 (30 microM). 7. It is concluded that relaxation of smooth muscle preparations by YC-1 is mediated mainly by activation of soluble guanylyl cyclase and subsequent increase in cyclic GMP levels. The failure of YC-1 to affect cardiac Fc, levels of cyclic GMP, and I[Ca(L)] suggests that soluble guanylyl cyclase is not influenced by YC-1 in rat heart muscle or only barely present in this tissue.