Isolation and characterization of an atypical Mycoplasma gallisepticum strain showing a new mgc2 variant

Mycoplasma gallisepticum (MG) is an important pathogen of the poultry industry able to cause chronic respiratory disease in chickens and infectious sinusitis in turkeys. Despite the application of biosecurity measures and the availability of vaccines for chickens, monitoring systems routinely applied for MG detection are still essential for infection control. Pathogen isolation is time-consuming and not suitable for rapid detection, albeit it is a compulsory step for genetic typing and antimicrobial susceptibility evaluation of single strains. The mgc2 gene is a species-specific molecular target adopted by most of the PCR protocols available for MG diagnosis, which are also included in the WOAH Terrestrial Manual. We describe the case of an atypical MG strain, isolated in 2019 from Italian turkeys, characterized by an mgc2 sequence not detectable by common endpoint PCR primers. Considering the potential risk of false negative results during diagnostic screenings with the endpoint protocol, the authors propose an alternative mgc2 PCR endpoint protocol, named MG600, which should be considered as a further diagnostic tool.

MaxiK channel interactome reveals its interaction with GABA transporter 3 and heat shock protein 60 in the mammalian brain

Large conductance voltage and calcium-activated potassium (MaxiK) channels are activated by membrane depolarization and elevated cytosolic Ca(2+). In the brain, they localize to neurons and astrocytes, where they play roles such as resetting the membrane potential during an action potential, neurotransmitter release, and neurovascular coupling. MaxiK channels are known to associate with several modulatory proteins and accessory subunits, and each of these interactions can have distinct physiological consequences. To uncover new players in MaxiK channel brain physiology, we applied a directed proteomic approach and obtained MaxiK channel pore-forming α subunit brain interactome using specific antibodies. Controls included immunoprecipitations with rabbit immunoglobulin G (IgG) and with anti-MaxiK antibodies in wild type and MaxiK channel knockout mice (Kcnma1(-/-)), respectively. We have found known and unreported interactive partners that localize to the plasma membrane, extracellular space, cytosol and intracellular organelles including mitochondria, nucleus, endoplasmic reticulum and Golgi apparatus. Localization of MaxiK channel to mitochondria was further confirmed using purified brain mitochondria colabeled with MitoTracker. Independent proof of MaxiK channel interaction with previously unidentified partners is given for GABA transporter 3 (GAT3) and heat shock protein 60 (HSP60). In human embryonic kidney 293 cells containing SV40 T-antigen (HEK293T) cells, both GAT3 and HSP60 coimmunoprecipitated and colocalized with MaxiK channel; colabeling was observed mainly at the cell periphery with GAT3 and intracellularly with HSP60 with protein proximity indices of ∼ 0.6 and ∼ 0.4, respectively. In rat primary hippocampal neurons, colocalization index was identical for GAT3 (∼ 0.6) and slightly higher for HSP60 (∼ 0.5) association with MaxiK channel. The results of this study provide a complete interactome of MaxiK channel the mouse brain, further establish the localization of MaxiK channel in the mouse brain mitochondria and demonstrate the interaction of MaxiK channel with GAT3 and HSP60 in neurons. The interaction of MaxiK channel with GAT3 opens the possibility of a role of MaxiK channel in GABA homeostasis and signaling.

Detection of Pseudomonas syringae pv actinidiae in kiwifruit pollen samples

Presence of Pseudomonas syringae pv actinidiae (Psa) the causal agent of bacterial canker of kiwifruit in pollen samples collected from infected and non infected orchards in Italy and in New Zealand was determined by polymerase chain reaction (PCR) and by direct bacterial isolation Psa was isolated only from pollen samples collected in Italy including pollen collected from two uninfected orchards which the following year showed signs of infection Psa was also detected in pollen collected from male and female vines in an Italian infected orchard Pollen samples from Italy but not from New Zealand were collected with a vacuum device Psa could not be isolated from any of the 25 New Zealand pollen samples analysed This is the first report of Psa being associated with pollen There is currently no evidence that artificial pollination leads to increased infection or that pollen has been responsible for the introduction of Psa in a previously Psafree area

Passive mechanical properties of cardiac tissues in heart hypertrophy during pregnancy

We evaluated changes in passive mechanical properties in cardiac tissues during rat pregnancy. Left and right ventricular free walls were dissected from hearts of nonpregnant, late-pregnant, and postpartum rats. Mechanical experiments in ventricular strips were done by stretch-release cycles using a step motor. The results show that during pregnancy, there is cardiac hypertrophy associated with (1) an increase in myocyte size, particularly of augmented myocyte length, (2) a decrease in passive tension developed by the myocardial walls, and (3) a decrease in both elastic modulus and hysteresis. All changes observed during rat pregnancy were reversed during postpartum. In conclusion, a heart with less ventricular rigidity could contribute to facilitating the ventricular filling in conditions of a greater circulating volume characteristic of pregnancy.

Endocytic trafficking signals in KCNMB2 regulate surface expression of a large conductance voltage and Ca2+-activated K+ channel

Large conductance voltage and calcium-activated K(+) channels play critical roles in neuronal excitability and vascular tone. Previously, we showed that coexpression of the transmembrane beta2 subunit, KCNMB2, with the human pore-forming alpha subunit of the large conductance voltage and Ca(2+)-activated K(+) channel (hSlo) yields inactivating currents similar to those observed in hippocampal neurons [Hicks GA, Marrion NV (1998) Ca(2+)-dependent inactivation of large conductance Ca(2+)-activated K(+) (BK) channels in rat hippocampal neurones produced by pore block from an associated particle. J Physiol (Lond) 508 (Pt 3):721-734; Wallner M, Meera P, Toro L (1999b) Molecular basis of fast inactivation in voltage and Ca(2+)-activated K(+) channels: A transmembrane beta-subunit homolog. Proc Natl Acad Sci U S A 96:4137-4142]. Herein, we report that coexpression of beta2 subunit with hSlo can also modulate hSlo surface expression levels in HEK293T cells. We found that, when expressed alone, beta2 subunit appears to reach the plasma membrane but also displays a distinct intracellular punctuated pattern that resembles endosomal compartments. beta2 Subunit coexpression with hSlo causes two biological effects: i) a shift of hSlo's intracellular expression pattern from a relatively diffuse to a distinct punctated cytoplasmic distribution overlapping beta2 expression; and ii) a decrease of hSlo surface expression that surpassed an observed small decrease in total hSlo expression levels. beta2 Site-directed mutagenesis studies revealed two putative endocytic signals at the C-terminus of beta2 that can control expression levels of hSlo. In contrast, a beta2 N-terminal consensus endocytic signal had no effect on hSlo expression levels. Thus, beta2 subunit not only can influence hSlo currents but also has the ability to limit hSlo surface expression levels via an endocytic mechanism. This new mode of beta2 modulation of hSlo may depend on particular coregulatory mechanisms in different cell types.

KCNMB1 regulates surface expression of a voltage and Ca2+-activated K+ channel via endocytic trafficking signals

Voltage-dependent and calcium-activated K(+) (MaxiK, BK) channels are ubiquitously expressed and have various physiological roles including regulation of neurotransmitter release and smooth muscle tone. Coexpression of the pore-forming alpha (hSlo) subunit of MaxiK channels with a regulatory beta1 subunit (KCNMB1) produces noninactivating currents that are distinguished by high voltage/Ca(2+) sensitivities and altered pharmacology [McManus OB, Helms LM, Pallanck L, Ganetzky B, Swanson R, Leonard RJ (1995) Functional role of the beta subunit of high conductance calcium-activated potassium channels. Neuron 14:645-650; Wallner M, Meera P, Ottolia M, Kaczorowski G, Latorre R, Garcia ML, Stefani E, Toro L (1995) Characterization of and modulation by a beta-subunit of a human maxi K(Ca) channel cloned from myometrium. Receptors Channels 3:185-199]. We now show that beta1 can regulate hSlo traffic as well, resulting in decreased hSlo surface expression. beta1 subunit expressed alone is able to reach the plasma membrane; in addition, it exhibits a distinct intracellular punctated pattern that colocalizes with an endosomal marker. Coexpressing beta1 subunit with hSlo, switches hSlo's rather diffuse intracellular expression to a punctate cytoplasmic localization that overlaps beta1 expression. Furthermore, coexpressed beta1 subunit reduces steady-state hSlo surface expression. Site-directed mutagenesis underscores a role of a putative endocytic signal at the beta1 C-terminus in the control of hSlo surface expression. We propose that aside from its well-established role as regulator of hSlo electrical activity, beta1 can regulate hSlo expression levels by means of an endocytic mechanism. This highlights a new beta1 subunit feature that regulates hSlo channels by a trafficking mechanism.

An endoplasmic reticulum trafficking signal prevents surface expression of a voltage- and Ca2+-activated K+ channel splice variant

Protein delivery to restricted plasma membrane domains is exquisitely regulated at different stages of the cell trafficking machinery. Traffic control involves the recognition of export/retention/retrieval signals in the endoplasmic reticulum (ER)/Golgi complex that will determine protein fate. A splice variant (SV), SV1, of the voltage- and Ca(2+)-activated K(+) channel alpha-subunit accumulates the channel in the ER, preventing its surface expression. We show that SV1 insert contains a nonbasic, hydrophobic retention/retrieval motif, CVLF, that does not interfere with proper folding and tetramerization of SV1. Localization of proteins in the ER by CVLF is independent of its position; originally, on the first internal loop, SV1 insert or CVLF perform equally well if placed at the middle or end of the alpha-subunit intracellular carboxyl terminus. Also, CVLF is able to restrict the traffic of an independently expressed transmembrane protein, beta 1-subunit. CVLF is present in proteins across species and in lower organisms. Thus, CVLF may have evolved to serve as a regulator of cellular traffic.

Differential expression of α1 and β subunits of voltage dependent Ca2+ channel at the neuromuscular junction of normal and p/q Ca2+ channel knockout mouse

Voltage-dependent calcium channels (VDCC) have a key role in neuronal function transforming the voltage signals into intracellular calcium signals. They are composed of the pore-forming alpha(1) and the regulatory alpha(2)delta, gamma and beta subunits. Molecular and functional studies have revealed which alpha(1) subunit gene product is the molecular constituent of each class of native calcium channel (L, N, P/Q, R and T type). Electrophysiological and immunocytochemical studies have suggested that at adult mouse motor nerve terminal (MNT) only P/Q type channels, formed by alpha(1A) subunit, mediate evoked transmitter release. The generation of alpha(1A)-null mutant mice offers an opportunity to study the expression and localization of calcium channels at a synapse with complete loss of P/Q calcium channel. We have investigated the expression and localization of VDCCs alpha(1) and beta subunits at the wild type (WT) and knockout (KO) mouse neuromuscular junction (NMJ) using fluorescence immunocytochemistry. The alpha(1A) subunit was observed only at WT NMJ and was absent at denervated muscles and at KO NMJ. The subunits alpha(1B), alpha(1D) and alpha(1E) were also present at WT NMJ and they were over- expressed at KO NMJ suggesting a compensatory expression due to the lack of the alpha(1A). On the other hand, the beta(1b), beta(2a) and beta(4) were present at the same levels in both genotypes. The presence of other types of VDCC at WT NMJ indicate that they may play other roles in the signaling process which have not been elucidated and also shows that other types of VDCC are able to substitute the alpha(1A) subunit, P/Q channel under certain pathological conditions.

Long-term and preventive effects of sublingual allergen-specific immunotherapy: a retrospective, multicentric study

There is now an increasing body of evidence to support the practice of allergen-specific sublingual-swallow immunotherapy (SLIT) in the treatment of IgE-mediated respiratory allergies. Recent studies on traditional injection therapy have pointed out that this form of treatment is not only capable to decrease actual allergic symptoms, but may also have long-term clinical and preventive effects and may influence atopy natural history. In the year 2000, our group published a retrospective, multicenter study showing the efficacy and safety of SLIT in a survey of 302 patients. We now carried out a second study on the same patients, with the aim of investigating long-term and preventive effects of SLIT. Beside the well-known safety and efficacy of this treatment (80.8% of patients reported clinical benefits), SLIT proved also to elicit long term clinical effects: over a mean follow-up of 11.6 months after the end of treatment, 80.8% of patients still maintained the previously achieved benefits. During the follow-up period, only 1% of non-asthma patients reported an onset of respiratory symptoms, and only 9.6% of patients undergoing new skin tests showed new sensitizations. All the clinical benefits were strongly linked to the length of treatment: patients with long-lasting benefits were treated for a mean length of 29.1 months, while patients showing a return to pre-SLIT condition were treated for a mean 13.3 months. SLIT can obtain long-term and preventive effects so far attributed to injection immunotherapy.

Cell contact-dependent PMN HLA-DR and CD69 membrane expression induced by autologous mono-lymphocytes and cell lines

Polymorphonuclear granulocytes (PMN) are commonly considered short-lived cells playing an efficient role in primary host defense via phagocytosis and release of cytotoxic compounds and inflammatory cytokines. Purified PMN do not express HLA-DR and CD69 molecules on cell surface, but they can be induced to do so by co-culture with peripheral blood derived mono-lymphocytes. De novo cell-surface expression of HLA-DR was also induced in PMN by co-culture with cell lines of lymphoid phenotype, but not with cell lines of myeloid phenotype. CD69 expression was not induced by co-culture with any of the cell lines used in the present study. In addition, we have observed induction of HLA-DR surface expression on PMN by culture in presence of culture supernatant of one of the cell lines of lymphoid origin, RPMI-8866. Quantitative analysis of HLA-DR and CD69 expression in stimulated PMN allowed us to divide PMN donors in two main groups, one with low expression and the other with high expression of the two molecules. HLA-DR surface expression was not altered by treatment with CHX and BFA, and RT-PCR analysis of total RNA from resting and stimulated PMN with RPMI-8866 supernatant did not detect the presence of any specific HLA-DR and CIITA transcript. Flow-cytometry and fluorescence microscopy analysis of resting PMN revealed the presence of HLA-DR molecules localized in intracellular vesicular-tubular structures. These data show that a reservoir of HLA-DR molecules is stored in the cytoplasm of human resting PMN and can be released to reach cell surface by a mobilization mechanism induced by cell surface interactions with selected cell types and sometimes with molecules released in culture supernatants.

External pore collapse as an inactivation mechanism for Kv4.3 K+ channels

Kv4 channels are thought to lack a C-type inactivation mechanism (collapse of the external pore) and to inactivate as a result of a concerted action of cytoplasmic regions of the channel. To investigate whether Kv4 channels have outer pore conformational changes during the inactivation process, the inactivation properties of Kv4.3 were characterized in 0 mM and in 2 mM external K+ in whole-cell voltage-clamp experiments. Removal of external K+ increased the inactivation rates and favored cumulative inactivation by repetitive stimulation. The reduction in current amplitude during repetitive stimulation and the faster inactivation rates in 0 mM external K+ were not due to changes in the voltage dependence of channel opening or to internal K+ depletion. The extent of the collapse of the K+ conductance upon removal of external K+ was more pronounced in NMG+-than in Na+-containing solutions. The reduction in the current amplitude during cumulative inactivation by repetitive stimulation is not associated with kinetic changes, suggesting that it is due to a diminished number of functional channels with unchanged gating properties. These observations meet the criteria for a typical C-type inactivation, as removal of external K+ destabilizes the conducting state, leading to the collapse of the pore. A tentative model is presented, in which K+ bound to high-affinity K+-binding sites in the selectivity filter destabilizes an outer neighboring K+ modulatory site that is saturated at approximately 2 mM external K+. We conclude that Kv4 channels have a C-type inactivation mechanism and that previously reported alterations in the inactivation rates after N- and C- termini mutagenesis may arise from secondary changes in the electrostatic interactions between K+-binding sites in the selectivity filter and the neighboring K+-modulatory site, that would result in changes in its K+ occupancy.

Remodeling of Kv4.3 potassium channel gene expression under the control of sex hormones

Kv4.3 channels are important molecular components of transient K(+) currents (Ito currents) in brain and heart. They are involved in setting the frequency of neuronal firing and heart pacing. Altered Kv4.3 channel expression has been demonstrated under pathological conditions like heart failure indicating their critical role in heart function. Thyroid hormone studies suggest that their expression in the heart may be hormonally regulated. To explore the possibility that sex hormones control Kv4.3 expression, we investigated whether its expression changes in the pregnant uterus. This organ represents a unique model to study Ito currents, because it possesses this type of K(+) current and undergoes dramatic changes in function and excitability during pregnancy. We cloned Kv4.3 channel from myometrium and found that its protein and transcript expression is greatly diminished during pregnancy. Experiments in ovariectomized rats demonstrate that estrogen is one mechanism responsible for the dramatic reduction in Kv4.3 expression and function prior to parturition. Furthermore, the reduction of plasma membrane Kv4.3 protein is accompanied by a perinuclear localization suggesting that cell trafficking is also controlled by sex hormones. Thus, estrogen remodels the expression of Kv4.3 in myometrium by directly diminishing its transcription and, indirectly, by altering Kv4.3 delivery to the plasma membrane.

A novel MaxiK splice variant exhibits dominant-negative properties for surface expression

We identified a novel MaxiK alpha subunit splice variant (SV1) from rat myometrium that is also present in brain. SV1 has a 33-amino acid insert in the S1 transmembrane domain that does not alter S1 overall hydrophobicity, but makes the S0-S1 linker longer. SV1 was transfected in HEK293T cells and studied using immunocytochemistry and electrophysiology. In non-permeabilized cells, N-terminal c-Myc- or C-terminal green fluorescent protein-tagged SV1 displayed no surface labeling or currents. The lack of SV1 functional expression was due to endoplasmic reticulum (ER) retention as determined by colabeling experiments with a specific ER marker. To explore the functional role of SV1, we coexpressed SV1 with the alpha (human SLO) and beta1 (KCNMB1) subunits of the MaxiK channel. Coexpression of SV1 inhibited surface expression of alpha and beta1 subunits approximately 80% by trapping them in the ER. This inhibition seems to be specific for MaxiK channel subunits since SV1 was unable to prevent surface expression of the Kv4.3 channel or to interact with green fluorescent protein. These results indicate a dominant-negative role of SV1 in MaxiK channel expression. Moreover, they reveal down-regulation by splice variants as a new mechanism that may contribute to the diverse levels of MaxiK channel expression in non-excitable and excitable cells.

Activation of Trp3 by inositol 1,4,5-trisphosphate receptors through displacement of inhibitory calmodulin from a common binding domain

Mammalian homologues of Drosophila Trp form plasma membrane channels that mediate Ca(2+) influx in response to activation of phospholipase C and internal Ca(2+) store depletion. Previous studies showed that human Trp3 is activated by inositol 1,4,5-trisphosphate (IP(3)) receptors (IP(3)Rs) and identified interacting domains, one on Trp and two on IP(3)R. We now find that Trp3 binds Ca(2+)-calmodulin (Ca(2+)/CaM) at a site that overlaps with the IP(3)R binding domain. Using patch-clamp recordings from inside-out patches, we further show that Trp3 has a high intrinsic activity that is suppressed by Ca(2+)/CaM under resting conditions, and that Trp3 is activated by the following: a Trp-binding peptide from IP(3)R that displaces CaM from Trp3, a myosin light chain kinase Ca(2+)/CaM binding peptide that prevents CaM from binding to Trp3, and calmidazolium, an inactivator of Ca(2+)/CaM. We conclude that inhibition of the inhibitory action of CaM is a key step of Trp3 channel activation by IP(3)Rs.

Decreased expression of voltage- and Ca(2+)-activated K(+) channels in coronary smooth muscle during aging

Aging is the main risk factor for coronary artery disease. One characteristic of aging coronary arteries is their enhanced contractile responses to endothelial vasoconstricting factors, which increase the risk of coronary vasospasm in older people. Because large-conductance voltage- and Ca(2+)-activated K(+) channels (MaxiK) are key regulators of vascular tone, we explored the possibility that this class of channels is diminished with increasing age. Using site-directed antibodies recognizing the pore-forming alpha subunit and electrophysiological methods, we demonstrate that the number of MaxiK channels is dramatically diminished in aged coronary arteries from old F344 rats. Channel density was reduced from 52+/-9 channels/pF (3 months old) to 18+/-5 channels/pF (25 to 30 months old), which represents a 65% reduction in the older population. Pixel intensity of Western blots was also diminished by approximately 50%. Moreover, the age-related decrease in the channel protein expression was also evident in humans, which showed approximately 80% reduction in 61- to 70-year-old subjects compared with 3- to 18-year-old youngsters and approximately 45% reduction compared with 19- to 56-year-old adults. In agreement with a reduction of MaxiK channel numbers in aging coronary arteries, old coronary arteries from F344 rats contract less effectively ( approximately 70% reduction) than young coronary arteries when exposed to the MaxiK channel blocker iberiotoxin. The contraction studies indicate that under physiological conditions, MaxiK channels are tonically active, serving as a hyperpolarizing force that opposes contraction. Thus, reduced expression of MaxiK channels in aged coronary arteries would lead to a decreased vasodilating capacity and increased risk of coronary spasm and myocardial ischemia in older people.

Expression of the alpha(2)delta subunit interferes with prepulse facilitation in cardiac L-type calcium channels

We investigated the role of the accessory alpha(2)delta subunit on the voltage-dependent facilitation of cardiac L-type Ca(2+) channels (alpha(1C)). alpha(1C) Channels were coexpressed in Xenopus oocytes with beta(3) and alpha(2)delta calcium channel subunits. In alpha(1C) + beta(3), the amplitude of the ionic current (measured during pulses to 10 mV) was in average approximately 1.9-fold larger after the application of a 200-ms prepulse to +80 mV. This phenomenon, commonly referred to as voltage-dependent facilitation, was not observed when alpha(2)delta was coexpressed with alpha(1C) + beta(3). In alpha(1C) + beta(3), the prepulse produced a left shift ( approximately 40 mV) of the activation curve. Instead, the activation curve for alpha(1C) + beta(3) + alpha(2)delta was minimally affected by the prepulse and had a voltage dependence very similar to the G-V curve of the alpha(1C) + beta(3) channel facilitated by the prepulse. Coexpression of alpha(2)delta with alpha(1C) + beta(3) seems to mimic the prepulse effect by shifting the activation curve toward more negative potentials, leaving little room for facilitation. The facilitation of alpha(1C) + beta(3) was associated with an increase of the charge movement. In the presence of alpha(2)delta, the charge remained unaffected after the prepulse. Coexpression of alpha(2)delta seems to set all the channels in a conformational state from where the open state can be easily reached, even without prepulse.

Safety and efficacy evaluation of sublingual allergen-specific immunotherapy a retrospective, multicenter study

In recent years, several controlled studies have proved the efficacy and safety of sublingual specific immunotherapy, as a possible alternative to the classic subcutaneous route of administration. This alternative option has been officially confirmed by the recent WHO position paper "Allergen Immunotherapy: Therapeutic Vaccines for Allergic Diseases'". Since sublingual immunotherapy has now been widely used for years, we carried out an open, multicentric, retrospective study to investigate the efficacy and safety of this form of treatment in a large number of patients. To this end, we studied 302 subjects undergoing sublingual immunotherapy for at least three months with different allergen compositions. Notwithstanding the obvious limitations due to the study design, this survey has confirmed the high efficacy and safety of this form of treatment, as already reported in previous controlled studies. Sublingual immunotherapy appears to be a simple, well-tolerated and effective method of treatment of allergen-specific diseases.

Hormonal control of protein expression and mRNA levels of the MaxiK channel alpha subunit in myometrium

Large conductance voltage-dependent and Ca(2+)-modulated K(+) channels play a crucial role in myometrium contractility. Western blots and immunocytochemistry of rat uterine sections or isolated cells show that MaxiK channel protein signals drastically decrease towards the end of pregnancy. Consistent with a transcriptional regulation of channel expression, mRNA levels quantified with the ribonuclease protection assay correlated well with MaxiK protein levels. As a control, Na(+)/K(+)-ATPase protein and RNA levels do not significantly change at different stages of pregnancy. The low numbers of MaxiK channels at the end of pregnancy may facilitate uterine contraction needed for parturition.

Complete reversal of run-down in rabbit cardiac Ca2+ channels by patch-cramming in Xenopus oocytes; partial reversal by protein kinase A

The rabbit cardiac Ca2+ channel (alpha1C) expressed in Xenopus oocytes exhibited a complete run-down of ionic currents when cell-attached patches were excised. The alpha1C channel was expressed alone or was coexpressed with the accessory beta2a or beta1b subunit. The catalytic subunit of protein kinase A (PKAc) and MgATP were capable of delaying the run-down of single-channel currents. In 33% of the alpha1C patches, and 26% of the alpha1C+beta2a patches, inclusion of PKAc in the bath solution delayed the run-down for a maximum of 20 min. In experiments where PKAc in the bath was not sufficient to delay the run-down of channel activity, insertion of the patch back into the oocyte (patch-cramming) could restore channel activity. Gating currents were also measured in the alpha1C+beta1b channel and were not subject to any run-down, even after the complete run-down of ionic currents. The results presented here reveal that PKAc is capable of delaying the run-down of currents in a subset of patches. The patch-cramming results suggest that a cytoplasmic factor, in addition to phosphorylation of the channel (by PKAc), may be involved in the maintenance of channel activity.

Substance P release in the dorsal horn assessed by receptor internalization: NMDA receptors counteract a tonic inhibition by GABA(B) receptors

Inhibitory amino acids have antinociceptive actions in the spinal cord that may involve inhibition of neurotransmitter release from primary afferents. Rat spinal cord slices with dorsal roots were used to study the effect of GABA and glycine on substance P release, assessed by the internalization of neurokinin 1 receptors. After electrical stimulation of the dorsal root at 100 Hz, about half of neurokinin 1 receptor-immunoreactive neurons in laminae I-IIo showed internalization. This internalization was inhibited by GABA (100 microM) and the GABA(B) agonist R-baclofen (10 microM), but not by the GABA(A) agonist muscimol (20 microM) or glycine (100 microM). The GABA(B) antagonist 2-hydroxysaclofen (100 microM) reversed the inhibitory effect of GABA, but not the GABA(A) antagonist bicuculline (100 microM). These findings demonstrate that GABA(B) receptors, but not GABA(A) or glycine receptors, inhibit substance P release induced by dorsal root stimulation. In contrast, R-baclofen did not inhibit the internalization produced by NMDA (100 microM), indicating that the stimulatory effect of NMDA receptors on substance P release is able to surmount the inhibitory effect of GABA(B) receptors. In the presence of the GABA(B) antagonist 2-hydroxysaclofen (100 microM), but not in its absence, stimulation of the dorsal root at 1 or 10 Hz was able to elicit internalization, which was not inhibited by the NMDA receptor antagonist AP-5 (50 microM) or the channel blocker MK-801 (10 microM). Therefore, inhibition of substance P release by GABA(B) receptors is tonic, and in its absence SP release no longer requires NMDA receptor activation.