Impact of pigeon pea biochar on cadmium mobility in soil and transfer rate to leafy vegetable spinach.

Introduction of heavy metals in the environment by various anthropogenic activities has become a potential treat to life. Among the heavy metals, cadmium (Cd) shows relatively high soil mobility and has high phyto-mammalian toxicity. Integration of soil remediation and ecosystem services, such as carbon sequestration in soils through organic amendments, may provide an attractive land management option for contaminated sites. The application of biochar in agriculture has recently received much attention globally due to its associated multiple benefits, particularly, long-term carbon storage in soil. However, the application of biochar from softwood crop residue for heavy metal immobilization, as an alternative to direct field application, has not received much attention. Hence, a pot experiment was conducted to study the effect of pigeon pea biochar on cadmium mobility in a soil-plant system in cadmium-spiked sandy loam soil. The biochar was prepared from pigeon pea stalk through a slow pyrolysis method at 300 °C. The experiment was designed with three levels of Cd (0, 5, and 10 mg Cd kg(-1) soil) and three levels of biochar (0, 2.5, and 5 g kg(-1) soil) using spinach as a test crop. The results indicate that with increasing levels of applied cadmium at 5 and 10 mg kg(-1) soil, the dry matter yield (DMY) of spinach leaf decreased by 9.84 and 18.29 %, respectively. However, application of biochar (at 2.5 and 5 g kg(-1) soil) significantly increased the dry matter yield of spinach leaf by 5.07 and 15.02 %, respectively, and root by 14.0 and 24.0 %, respectively, over the control. Organic carbon content in the post-harvest soil increased to 34.9 and 60.5 % due to the application of biochar 2.5 and 5 g kg(-1) soil, respectively. Further, there was a reduction in the diethylene triamine pentaacetic acid (DTPA)-extractable cadmium in the soil and in transfer coefficient values (soil to plant), as well as its concentrations in spinach leaf and root, indicating that cadmium mobility was decreased due to biochar application. This study shows that pigeon pea biochar has the potential to increase spinach yield and reduce cadmium mobility in contaminated sandy soil.

Effect of ATP on smooth muscle of toad urinary bladder.

Adenosine 5'-triphosphate (ATP), at a dose range of 1.8 to 116 microM, produced an initial phasic contraction followed by a rhythmic contraction in urinary bladder smooth muscle of the toad (Bufo melanostictus). Acetylcholine produced a rhythmic contraction which was antagonized by atropine (1.5 microM) and potentiated by neostigmine (1.7 microM), indicating activation of muscarinic receptors. However, both phasic and rhythmic components of ATP contraction were atropine-resistant. Quinidine (26-264 M) abolished the responses to ATP and acetylcholine, while indomethacin (28 microM) and theophylline (55 microM) antagonized only the acetylcholine responses. Repeated application of alpha, beta-methylene ATP desensitized the receptors and completely abolished contraction. ATP did not produce a phasic contraction in alpha, beta-methylene ATP-desensitized tissue, indicating that both ATP and its alpha, beta-methylene analogue occupy the same receptor site for phasic contraction. On the other hand, the rhythmic contraction induced by ATP remained unaffected in alpha, beta-methylene ATP-treated tissue. The phasic contraction in response to ATP can be blocked by verapamil (4 microM), but rhythmic contraction can only be abolished by a high concentration of verapamil (16 microM). Moreover, ATP produced no response in Ca+(+)-free or EGTA-containing solution, showing thereby that contractile responses to ATP are dependent upon extracellular Ca(+)+. These results indicate that the phasic component is a P2x-receptor-activated response while the rhythmic component might be an opening of calcium ion channels, either by depolarization of the membrane or by some unknown mechanism.

Effects of nicotine on spontaneous contractions of isolated atria of toad (Bufo melanostictus).

In toad atria, nicotine, at low concentrations (6.1 X 10(-6) M to 6.2 X 10(-5) M), produced a negative inotropic effect, and, at high concentrations (6.2 X 10(-4) M to 3.1 X 10(-3) M), a positive inotropic effect. The negative inotropism was potentiated by physostigmine or neostigmine and was antagonized by atropine or hemicholinium-3. The positive inotropism remained unaffected by exposure to phenoxybenzamine, phentolamine, propranolol, guanethidine, bretylium, hexamethonium, hemicholinium-3 or pretreatment with 6-OHDA or tyramine tachyphylaxis. The positive inotropism was antagonized by ethylene diamine tetraethyl acetate, verapamil or calcium-free Ringer. Caffeine induced positive inotropic effects, which were antagonized only by EDTA, and remained unaffected by exposure to verapamil or calcium-free Ringer. These results suggest a cholinergic mechanism for the negative inotropism produced by low concentrations of nicotine and also that the primary site of action of nicotine, when added at high concentrations, is the sarcolemmal calcium channel of toad atria resulting in increased calcium influx. They further suggest that the nicotine-induced positive inotropism is not mediated through activation of atrial adrenoceptors, ganglionic activation, presynaptic liberation of acetylcholine or liberation of catecholamine from sympathetic nerve endings.

Pharmacological and electrophysiological analysis of the effects of nicotine on cat blood pressure.

Nicotine (20-60 micrograms/kg) produced an initial vasodepressor response followed by a vasopressor response in anaesthetized cats, the mechanism of which was investigated. The vasodepressor response was antagonized by atropine or by vagotomy and was potentiated by physostigmine or neostigmine. Nicotine increased the single unit activity of different peripheral sympathetic nerves and evoked contraction of nictitating membrane and spleen along with vasopressor response. The vasopressor response was antagonized by phentolamine, prazosin, guanethidine, bretylium, 6-OHDA, hemicholinium-3 or hexamethonium. Propranolol or atenolol pretreatment potentiated the vasodepressor response and was antagonized by atropine. Desensitization by salbutamol did not modify the response to nicotine. The biphasic response to nicotine remained unaltered in yohimbine pretreated, in adrenalectomized, and in acute spinal as well as in decapitated animals; intracarotid or intracerebroventricular administration of nicotine did not produce any response. The biphasic response to nicotine does not involve the stimulation of the central vasomotor centre. In conclusion, these results suggest that the vasodepressor response is due to the vagal cholinergic mechanism. The vasopressor response is a consequence of activation of different peripheral adrenergic nerves causing increased release of the adrenergic transmitter at the neuroeffector region and the alpha 1-adrenoceptor mediate vasoconstriction in the systemic vascular bed.

The role of calcium channel in the effect of nicotine on contractility in isolated toad ventricle.

The mechanism of the positive inotropic effect produced by nicotine (6.2 X 10(-5) mol/l to 4.9 X 10(-4) mol/l) on electrically driven toad ventricles was investigated. The response to nicotine was not affected by 6-hydroxydopamine pretreatment, bretylium (2.4 X 10(-4) mol/l) exposure or tyramine tachyphylaxis. Following desensitisation by isoprenaline (4.2 X 10(-6) mol/l) of the beta-adrenoceptor in the ventricles, the response to nicotine was no affected. However, the response was antagonised by ethylene diamine tetraethyl acetate (2.3 X 10(-4) mol/l), verapamil (0.4 X 10(-5) mol/l) or calcium-free Ringer. Nicotine prolonged the action potential duration and enhanced the force of contraction. Nicotine induced slow action potentials in partially depolarized (in high potassium solution) ventricles and this was antagonised by verapamil (0.4 X 10(-5) mol/l). These results suggest that the effects of nicotine are mediated by a direct interaction with the Ca2+ channels at the cell surface.

The effects of nicotine on spontaneous contractions of cat urinary bladder in situ.

Nicotine and dimethyl-phenylpiperazinium (DMPP) increased intravesicular pressure and then transiently depressed the spontaneous activity of the urinary bladder in chloralose anaesthetized cats. Adrenaline (5-10 micrograms kg-1), noradrenaline (5-20 micrograms kg-1) and isoprenaline (40-50 micrograms kg-1) which depressed spontaneous urinary bladder activity, were antagonized by the beta-receptor blocking agent propranolol (1 mg kg-1). Phenylephrine (10-30 micrograms kg-1) was ineffective on the urinary bladder though it increased the systemic blood pressure. This latter effect was blocked by the alpha-receptor blocking agent phentolamine (2 mg kg-1). Acetylcholine (2-8 micrograms kg-1) caused a marked fall in systemic blood pressure, which was potentiated by physostigmine, but failed to produce any response on the intravesicular pressure even after physostigmine (50-100 micrograms kg-1) treatment. ATP (2 mg kg-1) produced an increase in intravesicular pressure accompanied by a fall in systemic blood pressure. The increased intravesicular pressure was antagonized by quinidine (20 mg kg-1); however, the fall in blood pressure remained unaltered. The increased intravesicular pressure induced by nicotine (20-40 micrograms kg-1) or DMPP (50-100 micrograms kg-1) was not affected by phentolamine (2 mg kg-1), propranolol (1 mg kg-1) or guanethidine (15-20 mg kg-1). Physostigmine (50-100 micrograms kg-1), hemicholinium 3 (2 mg kg-1) or atropine (1 mg kg-1) were also unable to affect the response to nicotine. Hexamethonium (1 mg kg-1), reduced the amplitude of spontaneous bladder contractions and quinidine (20 mg kg-1) abolished the effect of nicotine. 7 Bilateral sectioning of the cervical sympathetic or hypogastric nerves did not alter the effect of nicotine or DMPP. Higher spinal cord transection (Cl-C2) blocked the spontaneous, as well as the nicotine- and DMPP-induced, contractions of the bladder. 8 It is concluded that the increase in intravesicular pressure induced by nicotine is atropineresistant and is not mediated either through adrenergic or cholinergic mechanisms. It is probable that a purinergic mechanism is involved, via the activation of P2-receptors present in the urinary bladder.

Positive inotropic effect of nicotine on electrically evoked contraction of isolated toad ventricle.

The mechanism of the responses of nicotine on electrically evoked contractions of the isolated spirally cut toad ventricle was investigated. Nicotine produced a concentration-dependent positive inotropic effect of the ventricle. Prior administration of propranolol, hexamethonium, hemicholinium-3 or guanethidine failed to antagonize the positive inotropic effect of nicotine, thus ruling out the possibility of the nicotine effect being mediated through activation of beta-adrenoceptors, ganglionic activation, presynaptic liberation of acetylcholine and liberation of norepinephrine from the sympathetic nerve endings respectively. The positive inotropic effect is probably mediated through mobilisation of calcium since prior incubation with verapamil--the calcium transport blocker, EDTA, which chelates the extracellular calcium and calcium-free Ringer prevented the positive inotropic effect of nicotine. These results suggest that the positive intropic effect of nicotine may presumably be due to the facilitating effects of nicotine on Ca++ exchange or mobilisation of membrane bound Ca++.