Percutaneous Large-Bore Pulmonary Thrombectomy with the FlowTriever Device: Initial Experience in Intermediate-High and High-Risk Patients.

OBJECTIVES: This retrospective cohort study investigates outcomes of patients with intermediate-high and high-risk pulmonary embolism (PE) who were treated with transfemoral mechanical thrombectomy (MT) using the large-bore Inari FlowTriever aspiration catheter system. MATERIAL AND METHODS: Twenty-seven patients (mean age 56.1 ± 15.3 years) treated with MT for PE between 04/2021 and 11/2021 were reviewed. Risk stratification was performed according to European Society of Cardiology (ESC) guidelines. Clinical and hemodynamic characteristics before and after the procedure were compared with the paired Student's t test, and duration of hospital stay was analyzed with the Kaplan-Meier estimator. Procedure-related adverse advents were assessed. RESULTS: Of 27 patients treated, 18 were classified as high risk. Mean right-to-left ventricular ratio on baseline CT was 1.7 ± 0.6. After MT, a statistically significant reduction in mean pulmonary artery pressures from 35.9 ± 9.6 to 26.1 ± 9.0 mmHg (p = 0.002) and heart rates from 109.4 ± 22.5 to 82.8 ± 13.8 beats per minute (p < 0.001) was achieved. Two patients died of prolonged cardiogenic shock. Three patients died of post-interventional complications of which a paradoxical embolism can be considered related to MT. One patient needed short cardiopulmonary resuscitation during the procedure due to clot displacement. Patients with PE as primary driver of clinical instability had a median intensive care unit (ICU) stay of 2 days (0.5-3.5 days). Patients who developed PE as a complication of an underlying medical condition spent 11 days (9.5-12.5 days) in the ICU. CONCLUSION: In this small study population of predominantly high-risk PE patients, large-bore MT without adjunctive thrombolysis was feasible with an acceptable procedure-related complication rate.

Inter- and Intrareader Agreement of NI-RADS in the Interpretation of Surveillance Contrast-Enhanced CT after Treatment of Oral Cavity and Oropharyngeal Squamous Cell Carcinoma.

BACKGROUND AND PURPOSE: The Neck Imaging Reporting and Data System was introduced to assess the probability of recurrence in surveillance imaging after treatment of head and neck cancer. This study investigated inter- and intrareader agreement in interpreting contrast-enhanced CT after treatment of oral cavity and oropharyngeal squamous cell carcinoma. MATERIALS AND METHODS: This retrospective study analyzed CT datasets of 101 patients. Four radiologists provided the Neck Imaging Reporting and Data System reports for the primary site and neck (cervical lymph nodes). The Kendall's coefficient of concordance (W), Fleiss κ (κF), the Kendall's rank correlation coefficient (τB), and weighted κ statistics (κw) were calculated to assess inter- and intrareader agreement. RESULTS: Overall, interreader agreement was strong or moderate for both the primary site (W = 0.74, κF = 0.48) and the neck (W = 0.80, κF = 0.50), depending on the statistics applied. Interreader agreement was higher in patients with proved recurrence at the primary site (W = 0.96 versus 0.56, κF = 0.65 versus 0.30) or in the neck (W = 0.78 versus 0.56, κF = 0.41 versus 0.29). Intrareader agreement was moderate to strong or almost perfect at the primary site (range τB = 0.67-0.82, κw = 0.85-0.96) and strong or almost perfect in the neck (range τB = 0.76-0.86, κw = 0.89-0.95). CONCLUSIONS: The Neck Imaging Reporting and Data System used for surveillance contrast-enhanced CT after treatment of oral cavity and oropharyngeal squamous cell carcinoma provides acceptable score reproducibility with limitations in patients with posttherapeutic changes but no cancer recurrence.

Ca2+ release from subplasmalemmal stores as a primary event during exocytosis in Paramecium cells.

A correlated electrophysiological and light microscopic evaluation of trichocyst exocytosis was carried out the Paramecium cells which possess extensive cortical Ca stores with footlike links to the plasmalemma. We used not only intra- but also extracellular recordings to account for polar arrangement of ion channels (while trichocysts can be released from all over the cell surface). With three widely different secretagogues, aminoethyldextran (AED), veratridine and caffeine, similar anterior Nain and posterior Kout currents (both known to be Ca(2+)-dependent) were observed. Direct de- or hyperpolarization induced by current injection failed to trigger exocytosis. For both, exocytotic membrane fusion and secretagogue-induced membrane currents, sensitivity to or availability of Ca2+ appears to be different. Current responses to AED were blocked by W7 or trifluoperazine, while exocytosis remained unaffected. Reducing [Ca2+]o to < or = 0.16 microM (i.e., resting [Ca2+]i) suppressed electrical membrane responses triggered with AED, while we had previously documented normal exocytotic membrane fusion. From this we conclude that the primary effect of AED (as of caffeine) is the mobilization of Ca2+ from the subplasmalemmal pools which not only activates exocytosis (abolished by iontophoretic EGTA injection) but secondarily also spatially segregated plasmalemmal Ca(2+)-dependent ion channels (indicative of subplasmalemmal [Ca2+]i increase, but irrelevant for Ca2+ mobilization). The 45Ca2+ influx previously observed during AED triggering may serve to refill depleted stores. Apart from the insensitivity of our system to depolarization, the mode of direct Ca2+ mobilization from stores by mechanical coupling to the cell membrane (without previous Ca(2+)-influx from outside) closely resembles the model currently discussed for skeletal muscle triads.

Microdomain Ca2+ activation during exocytosis in Paramecium cells. Superposition of local subplasmalemmal calcium store activation by local Ca2+ influx.

In Paramecium tetraurelia, polyamine-triggered exocytosis is accompanied by the activation of Ca2+-activated currents across the cell membrane (Erxleben. C., and H. Plattner. 1994. J. Cell Biol. 127:935-945). We now show by voltage clamp and extracellular recordings that the product of current x time (As) closely parallels the number of exocytotic events. We suggest that Ca2+ mobilization from subplasmalemmal storage compartments, covering almost the entire cell surface, is a key event. In fact, after local stimulation, Ca2+ imaging with high time resolution reveals rapid, transient, local signals even when extracellular Ca2+ is quenched to or below resting intracellular Ca2+ concentration ([Ca2+]e, < or = [Ca2+]i). Under these conditions, quenched-flow/freeze-fracture analysis shows that membrane fusion is only partially inhibited. Increasing [Ca2+], alone, i.e., without secretagogue, causes rapid, strong cortical increase of [Ca2+]i but no exocytosis. In various cells, the ratio of maximal vs. minimal currents registered during maximal stimulation or single exocytotic events, respectively, correlate nicely with the number of Ca stores available. Since no quantal current steps could be observed, this is again compatible with the combined occurrence of Ca2+ mobilization from stores (providing close to threshold Ca2+ levels) and Ca2+ influx from the medium (which per se does not cause exocytosis). This implies that only the combination of Ca2+ flushes, primarily from internal and secondarily from external sources, can produce a signal triggering rapid, local exocytotic responses, as requested for Paramecium defense.

Stretch-activated current through single ion channels in the abdominal stretch receptor organ of the crayfish.

Single stretch-activated ion channels were studied on the soma and primary dendrites of stretch receptor neurons of the crayfish Orconectes limosus. When the membrane of the patch was deformed by applying suction to the pipette, a marked nonlinear increase in single-channel activity could be observed in two types of channels. These were indistinguishable on the basis of their single-channel conductances but differed in their voltage range of activation. One type showed strong inward rectification (RSA channel) and the second type was largely voltage independent (SA channel). A linear relationship was found between negative pressure and the natural logarithm of the channels' open probability. For an e-fold change in pressure, the average sensitivity was 8.7 +/- 0.4 (SD, n = 5) mmHg for the RSA channel and 5.6 +/- 2.2 (n = 5) mmHg for the SA channel. Both channels were found to be permeable to mono- and divalent cations. Current-voltage relationships were linear with slope conductances for the SA channel of: 71 +/- 11 (SD, n = 3) pS for K+, 50 +/- 7.4 (n = 5) pS for Na+, and 23 pS for Ca++. Similar values were found for the RSA channel. The data suggest that the SA channel is responsible for the mechanotransduction process in the stretch receptor neuron.

Charybdotoxin selectively blocks small Ca-activated K channels in Aplysia neurons.

The action of charybdotoxin (ChTX), a peptide component isolated from the venom of the scorpion Leiurus quinquestriatus, was investigated on membrane currents of identified neurons from the marine mollusk, Aplysia californica. Macroscopic current recordings showed that the external application of ChTX blocks the Ca-activated K current in a dose- and voltage-dependent manner. The apparent dissociation constant is 30 nM at V = -30 mV and increases e-fold for a +50- to +70-mV change in membrane potential, which indicates that the toxin molecule is sensitive to approximately 35% of the transmembrane electric field. The toxin is bound to the receptor with a 1:1 stoichiometry and its effect is reversible after washout. The toxin also suppresses the membrane leakage conductance and a resting K conductance activated by internal Ca ions. The toxin has no significant effect on the inward Na or Ca currents, the transient K current, or the delayed rectifier K current. Records from Ca-activated K channels revealed a single channel conductance of 35 +/- 5 pS at V = 0 mV in asymmetrical K solution. The channel open probability increased with the internal Ca concentration and with membrane voltage. The K channels were blocked by submillimolar concentrations of tetraethylammonium ions and by nanomolar concentrations of ChTX, but were not blocked by 4-aminopyridine if applied externally on outside-out patches. From the effects of ChTX on K current and on bursting pacemaker activity, it is concluded that the termination of bursts is in part controlled by a Ca-activated K conductance.

A dihydropyridine-sensitive voltage-dependent calcium channel in the sarcolemmal membrane of crustacean muscle.

Single-channel currents through calcium channels in muscle of a marine crustacean, the isopod Idotea baltica, were investigated in cell-attached patches. Inward barium currents were strongly voltage-dependent, and the channels were closed at the cell's resting membrane potential. The open probability (Po) increased e-fold for an 8.2 mV (+/- 2.4, n = 13) depolarization. Channel opening were mainly brief (< 0.3 ms) and evenly distributed throughout 100-ms pulses. Averaged, quasimacroscopic currents showed fast activation and deactivation and did not inactivate during 100-ms test pulses. Similarly, channel activity persisted at steadily depolarized holding potentials. With 200 mM Ba2+ as charge carrier, the average slope conductance from the unitary currents between +30 and +80 mV, was 20 pS (+/- 2.6, n = 12). The proportion of long openings, which were very infrequent under control conditions, was greatly increased by preincubation of the muscle fibers with the calcium channel agonist, the dihydropyridine Bay K8644 (10-100 microM). Properties of these currents resemble those through the L-type calcium channels of mammalian nerve, smooth muscle, and cardiac muscle cells.

Calcium-dependent inactivation of the dihydropyridine-sensitive calcium channels in GH3 cells.

The inactivation of calcium channels in mammalian pituitary tumor cells (GH3) was studied with patch electrodes under voltage clamp in cell-free membrane patches and in dialyzed cells. The calcium current elicited by depolarization from a holding potential of -40 mV passed predominantly through one class of channels previously shown to be modulated by dihydropyridines and cAMP-dependent phosphorylation (Armstrong and Eckert, 1987). When exogenous calcium buffers were omitted from the pipette solution, the macroscopic calcium current through those channels inactivated with a half time of approximately 10 ms to a steady state level 40-75% smaller than the peak. Inactivation was also measured as the reduction in peak current during a test pulse that closely followed a prepulse. Inactivation was largely reduced or eliminated by (a) buffering free calcium in the pipette solution to less than 10(-8) M; (b) replacing extracellular calcium with barium; (c) increasing the prepulse voltage from +10 to +60 mV; or (d) increasing the intracellular concentration of cAMP, either 'directly' with dibutyryl-cAMP or indirectly by activating adenylate cyclase with forskolin or vasoactive intestinal peptide. Thus, inactivation of the dihydropyridine-sensitive calcium channels in GH3 cells only occurs when membrane depolarization leads to calcium ion entry and intracellular accumulation.

Is the Outcome Indicator "3rd/4th Degree Perineal Tear in Spontaneous Singleton Births" a Reliable Quality Parameter in Obstetrics?

Obstetric sphincter damage is the most common cause of fecal incontinence in women. Between one-third and two-thirds of women who sustain a recognized third-degree tear during delivery subsequently suffer from fecal incontinence. We should therefore try to reduce the rate of high-grade tears as much as possible. But this rate can only be used as an outcome indicator for the quality of obstetric departments if the recognition and classification of sphincter injury is similar across departments in different hospitals.

Calcium influx through stretch-activated cation channels mediates adaptation by potassium current activation.

While stretch-sensitive channels are found in many cells, their physiological significance is still controversial. Their ability to mediate receptor current adaptation, as predicted from macroscopic currents, was investigated to provide further evidence for their role in mechanoelectrical transduction. In sensory neurones of abdominal stretch receptor organs of crayfish, Ca2+ influx through stretch-activated channels is shown to activate potassium channels which are considered to be responsible for the fast phase of receptor current adaptation.

Nitric oxide augments voltage-activated calcium currents of crustacea (Idotea baltica) skeletal muscle.

Invertebrate skeletal muscle contraction is regulated by calcium influx through voltage-dependent calcium channels in the sarcolemmal membrane. In present study we investigated the effects of nitric oxide (NO) donors on calcium currents of single skeletal muscle fibres from the marine isopod, Idotea baltica, using two-electrode voltage clamp recording techniques. The NO donors, S-nitrosocysteine, S-nitroso-N-acetyl-penicillamine or hydroxylamine reversibly increased calcium inward currents in a time dependent manner. The increase of the current was prevented by methylene blue. Our experiments suggest that NO increases calcium inward currents. NO, by acting on calcium ion channels in the sarcolemmal membrane, therefore, may directly be involved in the modulation of muscle contraction.

Effects of the sea anemone Anemonia sulcata toxin II on skeletal muscle and on neuromuscular transmission.

Effects of anemone toxin II (ATX II) have been analysed on the neuromuscular junction of the frog and different twitch muscles. Amplitudes of evoked endplate potentials and endplate currents are increased by ATX II, without effects on the amplitudes of miniature endplate potentials and endplate currents resulting from ionophoretically applied transmitter. The increase in evoked transmitter release is due to an increase in quantal content caused by an effect of the toxin on the presynaptic action potentials. ATX II is also effective on muscle fibers. The action potentials of frog twitch muscles are reversibly prolonged by ATX II. Their rate of rise and amplitudes are increased, while there is no effect on resting membrane potential. Similarly, action potentials of fast twitch muscle (extensor digitorum longus, EDL) of the mouse are reversibly prolonged by ATX II. In slow twitch muscle (soleus, SOL) of the mouse the toxin induces repetitive action potentials following the generation of a single action potential. Tetrodotoxin resistant action potentials of both denervated EDL and SOL are greatly and irreversibly prolonged by ATX II. The effects on muscle are due to a Na+ channel specific action of ATX II. Na+ current inactivation is slowed with the time constant tau h increasing towards positive membrane potentials. The steady state inactivation curve hoo was shifted to more positive potentials and its slope reduced.

Prevention of Labour-Associated Pelvic Floor Injuries - What is Known for Sure.

In order to avoid pelvic floor injuries a caesarean section is on the one hand often requested by the pregnant women and, on the other hand, offered by obstetric staff. For both forms of delivery, comprehensive risk-benefit analyses should be carried out before deciding in favour of the surgical procedure. The present brief review summarizes the current evidence on the avoidance of pelvic floor injuries.

Potassium channels in crustacean glial cells.

Unitary currents through single ion channels in the glial cells, which ensheath the abdominal stretch receptor neurons of the crayfish, were characterized with respect to their basic kinetic properties. In cell-attached and excised patches two types of Ca(++)-independent K+ channels were observed with slope conductances of 57 pS and 96 pS in symmetrical K+ solution. The 57 pS K+ channel was weakly voltage-dependent with a slope of the Po vs. membrane potential relationship of +95 mV for an e-fold change in Po. In addition to the main conductance level, the channel displayed conductance levels of 80 and 109 pS. In excised patches, channel activity of this "subconductance" K+ channel showed "rundown" that could be prevented with 2 mM ATP-Mg on the cytoplasmic side of the membrane. The 96 pS K+ channel was strongly voltage-dependent with a slope of +12 mV for an e-fold change in Po. Averaged single-channel currents elicited by voltage jumps proved the channel to be of the delayed rectifying type. Channel activity persisted in excised patches with minimal salt solution and in virtually Ca(++)-free saline. Because of its dependence on intracellular ATP-Mg, the subconductance K+ channel is discussed as a target of modulation by transmitters or peptides via phosphorylation of the channel.

Nitric oxide activates voltage-dependent potassium currents of crustacean skeletal muscle.

Nitric oxide (NO), a radical gas, acts as a multifunctional intra- and intercellular messenger. In the present study we investigated the effects of NO on muscle membrane potassium currents of isolated single muscle fibers from the marine isopods, Idotea baltica, using two-electrode voltage clamp recording techniques. Voltage-activated potassium currents consist of an outward current with fast activation and inactivation kinetics and a delayed, persistent outward current. Both currents were blocked by extracellular 4-aminopyridine and tetraethylammonium; the currents were not blocked by charybdotoxin or apamin. Application of the NO donors S-nitroso-N-acetylpenicillamine (SNAP) or hydroxylamine increased both the early and the delayed outward current in a dose- and time-dependent manner. PTIO, a NO scavenger, suppressed the effect of SNAP. N-Acetyl-dl-penicillamine, a related control compound which does not liberate NO, had no significant effect on outward currents. Methylene blue, a guanylyl cyclase inhibitor, prevented the increase of the outward current while 8-bromo-cGMP increased the current. Our experiments show that potassium currents of Idotea muscle are increased by NO donors. They suggest that NO by stimulating cGMP production mediates the effects on membrane currents involved in regulation of invertebrate muscle excitability.

Characteristics of spontaneous miniature and subminiature end-plate currents at the mouse neuromuscular junction.

1. Neuromuscular junctions of the mouse diaphragm were voltage clamped with a two-electrode voltage clamp in order to evaluate time characteristics of miniature end-plate currents (MEPCs). 2. The MEPCs fell into two amplitude classes: a larger class with an overall bell-shaped distribution (bell MEPCs) and a smaller class which forms a right-hand skew distribution (skew MEPCs). The mean MEPC amplitudes varied greatly because of the large range in the ratio of skew to bell MEPCs. This variation was greatest in neonate mice. 3. Rise time and time-to-peak were the same for MEPCs of the skew and bell classes. The MEPCs of both classes in neonate and adult mice had the same ratio of area (charge) over amplitude and the same time constant of decay. The absolute values changed with maturation (at 30 degrees C the ratio of area/amplitude was 4.5 +/- 0.8 ms in the newborn and 1.2 +/- 0.05 ms in the adult; the time constant of decay was 5.6 +/- 1.2 ms in the newborn and 0.8 +/- 0.05 ms in the adult). 4. Atypical MEPCs were found at all junctions. These had slow rising and falling phases, notches on the rising phases or a step the size of the sub-MEPC class. The number of atypical MEPCs increased during the experiment. 5. The data suggest that both skew and bell MEPC classes are released from the same presynaptic region and are generated by the same postsynaptic mechanism.

Subunit composition of the spontaneous miniature end-plate currents at the mouse neuromuscular junction.

1. Adult, neonate and young mouse diaphragm muscle fibres were voltage clamped with a two-electrode clamp. Miniature end-plate currents (MEPCs) were recorded on magnetic tape and analysed with a computer. The MEPC amplitude, charge, rise time, time-to-peak, decay time constant and root mean square (r.m.s.) noise level were determined for each MEPC. 2. The MEPC amplitude and charge distributions showed integral peaks starting from zero. Peaks were enhanced by selecting MEPCs with uniform time characteristics, with low noise, with increased sample size, with a curve smoothing routine and/or with a selected bin size. 3. Integral peaks were found in histograms from neonate, young and old mice. The ratio of sub-MEPCs to bell MEPCs decreased during neonatal development. 4. The size of the peak intervals was the same in all preparations of the same developmental stage. The adult modal peak varied between 8 and 12 times the subunit value, but peak intervals were similar (0.44 +/- 0.04 nA). 5. Changes in the holding potential or the bath temperature, or addition of an anticholinesterase agent, changed the peak interval. 6. The number of peaks in the overall MEPC amplitude and area-to-peak (charge) histogram profiles were usually the same. 7. Integral peaks on MEPC amplitude profiles, notches and steps on the MEPC rising phase and changes in the overall MEPC profiles are explained by a subunit composition of the quantum of transmitter release.

Voltage-clamp analysis of membrane currents and excitation-contraction coupling in a crustacean muscle.

A single fibre preparation from the extensor muscle of a marine isopod crustacean is described which allows the analysis of membrane currents and simultaneously recorded contractions under two-electrode voltage-clamp conditions. We show that there are three main depolarisation-gated currents, two are outward and carried by K+, the third is an inward Ca2+ current, I(Ca). Normally, the K+ currents which can be isolated by using K+ channel blockers, mask I(Ca). I(Ca) activates at potentials more positive than -40 mV, is maximal around 0 mV, and shows strong inactivation at higher depolarisation. Inactivation depends on current rather than voltage. Ba2+, Sr2+ and Mg2+ can substitute for Ca2+. Ba2+ currents are about 80% larger than Ca2+ currents and inactivate little. The properties of I(Ca) characterise it as a high threshold L-type current. The outward current consists primarily of a fast, transient A current, I(K(A)) and a maintained, delayed rectifier current, I(K(V)). In some fibres, a small Ca2+-dependent K+ current is also present. I(K(A)) activates fast at depolarisation above -45 mV, shows pronounced inactivation and is almost completely inactivated at holding potentials more positive than -40 mV. I(K(A)) is half-maximally blocked by 70 microM 4-aminopyridine (4-AP), and 70 mM tetraethylammonium (TEA). I(K(V)) activates more slowly, at about -30 mV, and shows no inactivation. It is half-maximally blocked by 2 mM TEA but rather insensitive to 4-AP. Physiologically, the two K+ currents prevent all-or-nothing action potentials and determine the graded amplitude of active electrical responses and associated contractions. Tension development depends on and is correlated with depolarisation-induced Ca2+ influx mediated by I(Ca). The voltage dependence of peak tension corresponds directly to the voltage dependence of the integrated I(Ca). The threshold potential for contraction is at about -38 mV. Peak tension increases with increasing voltage steps, reaches maximum at around 0 mV, and declines with further depolarisation.

Suppression of calcium current by an endogenous neuropeptide in neurones of Aplysia californica.

1. Actions of the neuropeptide FMRFamide (Phe-Met-Arg-Phe-NH2) and its derivative YGG-FMRFamide (Tyr-Gly-Gly-Phe-Met-Arg-Phe-NH2) on Ca2+ current were examined in identified, voltage-clamped neurones in the abdominal ganglion of Aplysia californica. 2. 'Puffed' application of either peptide at concentrations of 1-50 microM was followed by a transient partial suppression of pharmacologically isolated inward Ca2+ current elicited by a depolarizing step. At 20 degrees C, suppression was maximal 10-25 s following the brief puff of peptide, and lasted up to 90 s. Bath application of peptide had a steady suppressing effect, showing little if any desensitization. 3. Alternative sources of inward current suppression were ruled out, indicating that application of FMRFamide or YGG-FMRFamide produces a true decrease in Ca2+ current, rather than enhancement of possible contaminating outward (K+, H+ or Cl-) currents. 4. FMRFamide and YGG-FMRFamide were equally effective in suppressing Ca2+ current (apparent dissociation constant, KD* approximately 10 microM). However, only 30-50% of the total Ca2+ current elicited by voltage steps to above +10 mV appeared to be susceptible to suppression by even saturating concentrations of peptide. This, as well as a reduced effect of the peptides on Ca2+ current which was observed at potentials below +10 mV, may perhaps result from the presence of more than one class of Ca2+ channels, only one of which is sensitive to FMRFamide. 5. FMRFamide eliminated a constant fraction of Ca2+ current at all potentials above +10 mV, and had no direct effect on activation or inactivation of the remaining current. This behaviour is consistent with reduction in the number of functional Ca2+ channels by the peptide. 6. Suppression of Ca2+ current produced a concomitant depression of Ca2+-dependent K+ current, which was shown previously to be insensitive to FMRFamide when activated by direct ionophoretic injection of Ca2+ into the cell. 7. The effect of FMRFamide on Ca2+ current was normal following interference with or activation of known second-messenger systems, those involving adenosine 3',5'-cyclic monophosphate (cyclic AMP), cyclic GMP, Ca2+, inositol trisphosphate and protein kinase C. 8. Suppression of Ca2+ current by FMRFamide appeared to be mediated by the same receptor as enhancement by the peptide of K+ current resembling IK(S) (K+ current suppressed by serotonin), an effect seen in most of the same cells. Both effects of FMRFamide were mimicked by injection of guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S) into the cell, suggesting that the peptide may exert its effects by activating a guanosine 5'-triphosphate (GTP)-binding protein

Modulation of potassium conductances by an endogenous neuropeptide in neurones of Aplysia californica.

1. Macroscopic and single-channel currents were recorded from voltage-clamped neurones in the abdominal and pleural ganglia of Aplysia californica in order to investigate conductance changes elicited by application of the endogenous peptide FMRFamide (Phe-Met-Arg-Phe-NH2) and related neuropeptides to the cell surface. 2. The Ca-dependent K current, IK(Ca), when elicited at a constant voltage by intracellular injection of Ca2+, was insensitive to FMRFamide or its derivative YGG-FMRFamide (Tyr-Gly-Gly-Phe-Met-Arg-Phe-NH2). 3. Under steady voltage clamp, certain cells responded to a brief puff of FMRFamide or YGG-FMRFamide with a transient outward current lasting about 1 min. Unclamped cells responded with a corresponding hyperpolarization. These responses reversed at about -75 mV. Ion substitution indicated that the current is carried by K+. 4. FMRFamide and YGG-FMRFamide were equally effective in activating the outward current, whereas FMRF, met-enkephalin and leu-enkephalin were ineffective. 5. At voltages negative to -30 mV and, in the absence of extracellular Ca2+, also at more positive potentials, the FMRFamide-sensitive current showed no voltage dependence beyond that predicted from constant-field considerations. 6. The response to FMRFamide was relatively insensitive to extracellular tetraethylammonium (TEA, KD approximately 75 mM) and 4-aminopyridine (4-AP, KD approximately 6 mM). It was suppressed in Ba-containing solutions, but was unaffected by injection of the Ca chelating agent EGTA. The response was blocked by serotonin and other agents known to elevate intracellular adenosine 3',5'-phosphate (cyclic AMP) levels, and by direct injection of cyclic AMP into the cell. 7. In its pharmacological properties and lack of voltage dependence, the FMRFamide-activated current resembles the 'S' current, IK(S), a K current suppressed by application of serotonin in Aplysia neurones. 8. The similarity between the FMRFamide-sensitive current and the 'S' current was confirmed in cell-attached patch-clamp studies, in which activity of 'S' channels was found to be reduced by serotonin, and enhanced by FMRFamide. 9. Thus, FMRFamide may function in Aplysia to counteract the serotonergic modulation of 'S' channels, which has been proposed as a mechanism of presynaptic plasticity in this mollusc.