P2X receptors in sensory neurons co-cultured with cancer cells exhibit a decrease in opioid sensitivity.

Opioids are known to control the activity of P2X receptors in the sensory neurons of rats. These receptors are important in persistent pain signaling. However, there are extremely severe pain states, such as those associated with metastatic diseases, that are refractory to opioid treatment. We have tested the possibility that cancer cells affect the sensitivity of P2X(2/3) and P2X(2) receptors to opiates. The sensitivity of ATP-activated currents to the selective mu-opioid receptor agonist endomorphin-1 was evaluated in rat nodose neurons co-cultured (on separate coverslips) with fibrosarcoma cells (NCTC 2472) using whole-cell patch-clamp recordings. Both in control and in co-cultured neurons, P2X-mediated responses exhibited highly variable biphasic desensitization kinetics with fast and slow components. However, ATP-activated currents in co-cultured neurons acquired a new feature: the degree of their inhibition by endomorphin-1 demonstrated strong dependence on their desensitization kinetics. The neurons with 'slower' responses were subject to a smaller inhibitory effect of the opioid. The 'ultra-slow' responses completely lost their sensitivity to the opioid. The occurrence of such responses, rarely observed in the control neurons, was considerably increased with the duration of co-culturing. Application of endomorphin-1 to nodose neurons, co-cultured with rapidly proliferating but non-malignant cells (fibroblasts), resulted in data similar to those for the control. In summary, fibrosarcoma cells release diffusible factors altering the properties of desensitization kinetics of P2X receptors and, in particular, decrease their sensitivity to opioid inhibitory control. These phenomena may increase neuronal excitability initiated by peripheral ATP release and thereby contribute to the decreased sensitivity of cancer pain to opioids.

Differential effects of CB1 and opioid agonists on two populations of adult rat dorsal root ganglion neurons.

Inhibition of primary afferent neurons contributes to the antihyperalgesic effects of opioid and CB1 receptor agonists. Two bioassays were used to compare the effects of the CB1 receptor agonist CP 55,940 and morphine on dissociated adult rat DRG neurons. Both agonists inhibited the increase in free intracellular Ca2+ concentration evoked by depolarization; however, effects of CP 55,940 occurred primarily in large neurons (cell area, >800 microm2), whereas morphine inhibited the response in smaller neurons. Cotreatment with selective blockers of L-, N-, and P/Q-type voltage-dependent Ca2+ channels indicated that CB1 receptors on DRG neurons couple solely with N-type channels but opioid receptors couple with multiple subtypes. Experiments with selective agonists and antagonists of opioid receptors indicated that mu and delta, but not kappa, receptors contributed to the inhibitory effect of morphine on voltage-dependent Ca2+ influx. Because Ca2+ channels underlie release of transmitters from neurons, the effects of opioid agonists and CP 55,940 on depolarization-evoked release of calcitonin gene-related peptide (CGRP) were compared. Morphine inhibited release through delta receptors but CP 55,940 had no effect. Colocalization of CGRP with delta-opioid but not mu-opioid or CB1 receptor immunoreactivity in superficial laminae of the dorsal horn of the spinal cord was consistent with the data for agonist inhibition of peptide release. Therefore, CB1 and opioid agonists couple with different voltage-dependent Ca2+ channels in different populations of DRG neurons. Furthermore, differences occur in the distribution of receptors between the cell body and terminals of DRG neurons. The complementary action of CB1 and opioid receptor agonists on populations of DRG neurons provides a rationale for their combined use in modulation of somatosensory input to the spinal cord.

Cannabinoids attenuate depolarization-dependent Ca2+ influx in intermediate-size primary afferent neurons of adult rats.

CB1 receptors have been localized to primary afferent neurons, but little is known about the direct effect of cannabinoids on these neurons. The depolarization-evoked increase in the concentration of free intracellular calcium ([Ca(2+)](i)), measured by microfluorimetry, was used as a bioassay for the effect of cannabinoids on isolated, adult rat primary afferent neurons 20-28 h after dissociation of dorsal root ganglia. Cannabinoid agonists CP 55,940 (100 nM) and WIN 55,212-2 (1 microM) had no effect on the mean K(+)-evoked increase in [Ca(2+)](i) in neurons with a somal area<800 microm(2), but the ligands attenuated the evoked increase in [Ca(2+)](i) by 35% in neurons defined as intermediate in size (800-1500 microm(2)). The effects of CP 55,940 and WIN 55,212-2 were mediated by the CB1 receptor on the basis of relative effective concentrations, blockade by the CB1 receptor antagonist SR141716A and lack of effect of WIN 55,212-3. Intermediate-size neurons rarely responded to capsaicin (100 nM). Although cannabinoid agonists generally did not inhibit depolarization-evoked increases in [Ca(2+)](i) in small neurons, immunocytochemical studies indicated that CB1 receptor-immunoreactivity occurred in this population. CB1 receptor-immunoreactive neurons ranged in size from 227 to 2995 microm(2) (mean somal area of 1044 microm(2)). In double labeling studies, CB1 receptor-immunoreactivity co-localized with labeling for calcitonin gene-related peptide and RT97, a marker for myelination, in some primary afferent neurons. The decrease in evoked Ca(2+) influx indicates that cannabinoids decrease conductance through voltage-dependent calcium channels in a subpopulation of primary afferent neurons. Modulation of calcium channels is one mechanism by which cannabinoids may decrease transmitter release from primary afferent neurons. An effect on voltage-dependent calcium channels, however, represents only one possible effect of cannabinoids on primary afferent neurons. Identifying the mechanisms by which cannabinoids modulate nociceptive neurons will increase our understanding of how cannabinoids produce anti-nociception in normal animals and animals with tissue injury.

[Hypoxia as a modality to correct disturbances in bone oxygen uptake at various static-kinetic conditions]. / Gipoksiia kak sposob korrektsii narusheniia potrebleniia kisloroda kostnoi tkan'iu pri razlichnykh statokineticheskikh usloviiakh.

Osteodystrophy models consisted in removing weight loading from hind limbs and rats' immobilization; disturbances in bone oxygen uptake were quelled by induced gaseous environment with low PO2. Unloading of the hind limbs for 28 days was found to decrease oxygen uptake by fragments of the iliac bone, and oxygen pressure in m. gastrocnemius. These parameters were unchanged in atmosphere with 12% of oxygen. Motor restraint of rats in hypoxic atmosphere leads to less marked reductions in oxygen demand in iliac fragments and oxygen pressure in m. gastrocnemius as compared with breathing ambient air.

[Effect of inhalation of surface-active substances on the surfactant system of the lung]. / Vplyv ingaliatsii poverkhnevo-aktyvnykh rechovyn na stan surfaktantnoi systemy legen.

Surface activity, biochemical composition and morphology of the rat lungs were studied in norm, under effect of acute hypoxia and after infusion of obsidan (1 mg/100g). The data permit suggesting that under the influence of obsidan and hypoxia a stability index of surfactants and quantity of phospholipids decreased, while the quantity of lysophosphatidylcholine and lysophosphatidylethanolamine increased. Morphology studies show that after hypoxia and obsidan infusion oedema and cell destruction developed in the lung. The inhalation of exogenous surfactant increased stability index and quantity of phospholipids, decreased the quantity of lysophospholipids but did not eliminate morphological disorders in the lung induced by hypoxia and obsidan infusion.

[The effect of alpha-tocopherol on pulmonary surfactants]. / Vliianie alpha-tokoferola na surfaktanty legkogo.

Tocopherol deficiency in the rat organism stimulates activation of lipid peroxidation: the content of hydroperoxides in blood and surfactants of lungs tends to increase, the superweak glow of surfactant lipids enhances. In this case the surface activity of lung surfactants is lower than in the control. It also gets lower in hypervitaminosis rats. The data obtained may be used for development of approaches to the tocopherol (antioxidant) correlation of the lung surfactant system functioning.