Biochemical and biophysical analysis of cell-to-cell channels and regulation of gap junctional permeability

Descending vasa recta endothelium is an electrical syncytium

We examined gap junction coupling of descending vasa recta (DVR). DVR endothelial cells or pericytes were depolarized to record the associated capacitance transients. Virtually all endothelia and some pericytes exhibited prolonged transients lasting 10-30 ms. Carbenoxolone (100 microM) and 18beta-glycyrrhetinic acid (18betaGRA; 100 microM) markedly shortened the endothelial transients. Carbenoxolone and heptanol (2 mM) reduced the pericyte capacitance transients when they were prolonged. Lucifer yellow (LY; 2 mM) was dialyzed into the cytoplasm of endothelial cells and pericytes. LY spread diffusely along the endothelial monolayer, whereas in most pericytes, it was confined to a single cell. In some pericytes, complex patterns of LY spreading were observed. DVR cells were depolarized by voltage clamp as fluorescence of bis(1,3-dibarbituric acid)-trimethine oxanol [DiBAC(4)(3)] was monitored approximately 200 microm away. A 40-mV endothelial depolarization was accompanied by a 26.1 +/- 5.5-mV change in DiBAC(4)(3) fluorescence. DiBAC(4)(3) fluorescence did not change after 18betaGRA or when pericytes were depolarized. Similarly, propagated cytoplasmic Ca(2+) responses arising from mechanical perturbation of the DVR wall were attenuated by 18betaGRA or heptanol. Connexin (Cx) immunostaining showed predominant linear Cx40 and Cx43 in endothelia, whereas Cx37 stained smooth muscle actin-positive pericytes. We conclude that the DVR endothelium is an electrical syncytium and that gap junction coupling in DVR pericytes exists but is less pronounced.

Voltage clamp limitations of dual whole-cell gap junction current and voltage recordings. I. Conductance measurements

Previous correction methods for series access resistance errors in the dual whole-cell configuration did not take into account the effect of nonzero resting potentials (E(rest)) and junctional reversal potentials (E(rev)). Dual whole-cell currents were modeled according to resistor-circuit analysis and two correction formulas for the measurement of junctional currents (I(j)) were assessed. The equations for I(j), derived from Kirchoff's law before and after baseline subtraction of the nonjunctional current, were assessed for accuracy under a variety of whole-cell patch-clamp recording conditions. Both equations accurately correct for dual whole-cell voltage-clamp errors provided that the cellular parameters are included in the nonbaseline subtracted I(j) derivations. Junctional conductance (g(j)) estimates are most reliable at high junctional resistance (R(j)) values and minimize the need for corrective methods based on electrode series and cellular input resistances (R(el) and R(in)). In the "open-cell" configuration, low R(j) values relative to R(in) are required for accurate g(j) estimates. These methods provide the basis for accurate quantitative measurements of junctional resistance (or conductance) of gap junction channels or connexin hemichannels in the dual whole-cell or open-cell configurations. Revaluation of V(j)-dependent gating of rat connexin40 g(j) produced nearly identical Boltzmann fits to previously published data. Continuous g(j)-V(j) curves generated by variable slope V(j) ramps provide for more accurate fits and assessment of the time-dependence of the half-inactivation voltage and net gating charge movement.

Enhancement of connexin 43 expression increases proliferation and differentiation of an osteoblast-like cell line

Bone cells form a functional syncytium as they are coupled by gap junctions composed mainly of connexin 43 (Cx43). To further understand the role of Cx43 in bone cell growth and differentiation, we stably transfected Cx45-expressing UMR 106-01 cells with Cx43 using an expression vector containing rat Cx43 cDNA. Three stably transfected clones were analyzed, all of which showed altered expression of Cx43 and/or Cx45 as was obvious from immunocytochemistry and Northern blotting. Double whole-cell patch clamping revealed single-channel conductances of 20 (Cx45) and 60 pS (Cx43). The overexpression of Cx43 led to an increase in dye coupling concomitant with elevated gap-junctional conductance. The phenotype of the transfected clones was characterized by an increased proliferation (4- to 7-fold) compared to controls. Moreover, a transfectant clone with 10- to 12-fold enhanced Cx43 expression showed a significantly increased calcium content of the extracellular matrix and enlarged mineralization nodules, while alkaline phosphatase was moderately increased. We conclude that enhanced gap-junctional coupling via Cx43 significantly promotes proliferation and differentiation of UMR cells.

Intercellular communication between bone marrow stromal cells and CD34+ haematopoietic progenitor cells is mediated by connexin 43-type gap junctions

The existence of functional gap junctions between haematopoietic progenitor cells (HPCs) and stromal cells of the haematopoietic microenvironment in the human system is a controversial issue. Primary CD34+ HPCs isolated from leukapheresis products were co-incubated with the human fibroblastoid bone marrow stromal cell line L87/4 in short-term liquid culture. Using the highly sensitive double whole-cell patch-clamp technique, we found that the majority (91%) of CD34+ HPCs are electrically coupled to L87/4 cells. Importantly, efficient coupling was observed within 1 h of the attachment of CD34+ HPCs to plastic adherent L87/4 cells. By comparison, homologous cell pairs formed by L87/4 cells exhibited a significantly higher electric coupling. Analysis of single-channel conductances revealed an electric profile characteristic of connexin 43 (Cx43)-type gap junctions for both homologous and heterologous cell pairs. The Cx phenotype was confirmed using Cx43-specific monoclonal antibodies in a flow cytometric assay and reverse transcription polymerase chain reaction (RT-PCR) for the detection of Cx43 mRNA. Finally, the electrophysiological studies were complemented by dye-transfer experiments using the recently described 'parachute' technique that allows the monitoring of dye diffusion without disruption of the plasma membrane. Taken together, our data indicate that functional Cx43-type gap junctions exist between stromal cells and immature HPCs and, thus, may provide an important regulatory pathway in haematopoiesis.

PKC role in mechanically induced Ca2+ waves and ATP-induced Ca2+ oscillations in airway epithelial cells

Mechanical stimulation of airway epithelial cells generates the Ca2+ mobilization messenger inositol 1,4,5-trisphosphate and the protein kinase (PK) C activator diacylglycerol. Inositol 1,4,5-trisphosphate diffuses through gap junctions to mediate intercellular communication of the mechanical stimulus (a "Ca2+ wave"); the role that diacylglycerol-activated PKC might play in the response is unknown. Using primary cultures of rabbit tracheal cells, we show that 12-O-tetradecanoylphorbol 13-acetate- or 1, 2-dioctanyl-sn-glycerol-induced activation of PKC slows the Ca2+ wave, decreases the amplitude of induced intracellular free Ca2+ concentration ([Ca2+]i) increases, and decreases the number of affected cells. The PKC inhibitors bisindolylmaleimide and Gö 6976 slowed the spread of the wave but did not change the number of affected cells. We show that ATP-induced [Ca2+]i increases and oscillations, responses independent of intercellular communication, were inhibited by PKC activators. Bisindolylmaleimide decreased the amplitude of ATP-induced [Ca2+]i increases and blocked oscillations, suggesting that PKC has an initial positive effect on Ca2+ mobilization and then mediates feedback inhibition. PKC activators also reduced the [Ca2+]i increase that followed thapsigargin treatment, indicating a PKC effect associated with the Ca2+ release mechanism.

The long QT syndrome and torsade de pointes

The LQTS is a prime example of how molecular biology, ion channel, cellular, and organ physiology, coupled with clinical observations, promise to be the future paradigm for advancement of medical knowledge. Both the congenital and acquired LQTS are due to abnormalities (intrinsic and/or acquired) of the ionic currents underlying cardiac repolarization. In this review, the continually unraveling molecular biology of congenital LQTS is discussed. The various pharmacological agents associated with the acquired LQTS are listed. Although it is difficult to predict which patients are at risk for TdP, careful assessment of the risk-benefit ratio is important before prescribing drugs known to be able to cause QT prolongation. The in vivo electrophysiological mechanism of TdP in the LQTS is described using, as a paradigm, the anthopleurin-A canine model, a surrogate for LQT3. In the LQTS, prolonged repolarization is associated with increased spatial dispersion of repolarization. Prolongation of repolarization also acts as a primary step for the generation of EADs. The focal EAD induced triggered beat(s) can infringe on the underlying substrate of inhomogeneous repolarization to initiate polymorphic reentrant VT, sometimes having the characteristic twisting QRS configuration known as TdP. The review concludes by discussion of the clinical manifestations and current management of both the congenital and acquired LQTS. The initial therapy of choice for the large majority of patients with the congenital LQTS is a beta-blocking drug. This therapy seems to be effective in LQT1 and LQT2 patients, but may not be as effective in LQT3 patients. Other therapeutic options include pacemakers, cervicothoracic sympathectomy, and the implantable cardioverter defibrillator. Recent molecular genetic studies have suggested several genotype specific therapies; however, long-term efficacy data are not available.

Effects of vitamin D3, 17beta-estradiol, vasoactive intestinal peptide, and glutamate on electric coupling between rat osteoblast-like cells in vitro

Osteoblast-like cells express receptors for various hormones and neurotransmitters that induce widespread actions in the bone to which intercellular communication and its modulation may contribute. Therefore, we examined the effects of the osteotropic hormones vitamin D3 (vitD3) and 17beta-estradiol (17beta-E2) as well as the neurotransmitter vasoactive intestinal peptide (VIP) and the excitatory amino acid glutamate (Glu) on gap junctions between rat osteoblast-like (ROB) cells in vitro. Electric coupling was measured by simultaneous intracellular recordings from neighboring cells. The coupling factor (cf) was calculated from membrane potential changes induced by alternate current injections into both cells. In ROB cells cf was increased by 5 x 10(-8) mol/L vitD3 to 130 +/- 13% (mean +/- SD; n = 6) of the initial value within 5-20 min. This effect was not reversible after washing with control saline for 10-15 min. In six cell pairs, cf was not affected by vitD3 (94 +/- 5%). In three cell pairs superfusion of 10(-8) mol/L E2 reduced cf to 80 +/- 6% within 10 min, whereas, in two cell pairs, this hormone improved cf to 140% within 20 min. Exposure of VIP (3 x 10(-8) mol/L) did not alter cf in the majority of cells (99 +/- 3%; n = 11). In five cell pairs, cf was improved within 5-15 min to 133 +/- 12%, whereas, in one cell pair, cf was reduced to 22% by VIP. In contrast, brief application of Glu (5 x 10(-3) mol/L) decreased cf to 75 +/- 5% (n = 5), whereas, in nine other cell pairs, cf was not affected (96 +/- 5%). The findings indicate that cell-cell coupling of gap junctions between bone cells can be altered by actions of hormones and transmitters in a cell-pair-specific way, which may depend on their functional state.

Ultrastructure of the supporting cells in the paratympanic organ of chicken, Gallus gallus domesticus

The paratympanic organ is a specialized sensory organ of birds located in the medial wall of the tympanic cavity. It possesses a sensory epithelium formed by type II hair cells and supporting cells. The supporting cells are tall, narrow units that extend from the basement membrane to the free epithelial surface. They show a fine structure characterized by numerous mitochondria, a conspicuous Golgi complex and a well-developed RER. Moreover, some uncommon structures, probably formed by heaped RER cisternae, are frequently present in the cytoplasm. Adjacent supporting cells are connected by numerous and extensive gap junctions; moreover, small gap junctions between hair cell and supporting cells are to be found. The possible mechanical and metabolical functions of the paratympanic organ supporting cells are discussed.

Electrically induced vasomotor responses and their propagation in rat renal vessels in vivo

1. Vasomotor responses (VMR) induced by local electrical stimulation were studied in the vasculature of the split hydronephrotic rat kidney by in vivo microscopy. 2. Unipolar pulses, which were applied by a micropipette positioned close to the vessel wall, elicited local and propagated VMR. Depolarizing and hyperpolarizing currents caused vasoconstriction and vasodilatation, respectively. 3. The magnitude of VMR could be controlled within seconds by variation of pulse frequency, pulse width and voltage. VMR were abolished by slight retraction of the stimulating micropipette. Repetitive electrical stimulation resulted in reproducibly uniform VMR. 4. Propagated VMR decayed with increasing distance from the stimulation site. They decayed more rapidly in the upstream than in the downstream flow direction in interlobular arteries. The longitudinal decay was well approximated by an exponential function with significantly different length constants of 150 +/- 40 microns (upstream, n = 5) and 420 +/- 90 microns (downstream, n = 8). 5. Our results show that vasomotor responses, which are initiated by changes in membrane potential, are propagated over distances of potential physiological importance in interlobular arteries.

Modulation of Neisseria porin (PorB) by cytosolic ATP/GTP of target cells: parallels between pathogen accommodation and mitochondrial endosymbiosis

PorB of the pathogenic Neisseria species belongs to the large family of pore-forming proteins (porins) produced by gram-negative bacteria. PorB is exceptional in that it is capable of translocating vectorially into membranes of infected target cells and functions in the infection process. Here we report on an unexpected similarity between Neisserial PorB and mitochondrial porins. Both porin classes interact with purine nucleoside triphosphates, which down-regulate pore size and cause a shift in voltage dependence and ion selectivity. Patch-clamp analyses indicate that PorB channel activity is tightly regulated in intact epithelial cells. In light of recent findings on the pivotal role of PorB in virulence and the prevention of phagosome lysosome fusion, these data provide important mechanistic clues on the intracellular pathogen accommodation reminiscent of mitochondrial endosymbiosis.

Structure--function relationships in gap junctions

Gap junctions are metabolic and electrotonic pathways between cells and provide direct cooperation within and between cellular nets. They are among the cellular structures most frequently investigated. This chapter primarily addresses aspects of the assembly of the gap junction channel, considering the insertion of the protein into the membrane, the importance of phosphorylation of the gap junction proteins for coupling modulation, and the formation of whole channels from two hemichannels. Interactions of gap junctions with the subplasmalemmal cytoplasm on the one side and with tight junctions on the other side are closely considered. Furthermore, reviewing the significance and alterations of gap junctions during development and oncogenesis, respectively, including the role of adhesion molecules, takes up a major part of the chapter. Finally, the literature on gap junctions in the central nervous system, especially between astrocytes in the brain cortex and horizontal cells in the retina, is summarized and new aspects on their structure-function relationship included.

Astrocytes exhibit regional specificity in gap-junction coupling

Astrocytes are coupled to each other via gap-junctions both in vivo and in vitro. Gap-junction coupling is essential to a number of astrocyte functions including the spatial buffering of extracellular K+ and the propagation of Ca2+ waves. Using fluorescence recovery after photo-bleach, we quantitatively assayed and compared the coupling of astrocytes cultured from six different central nervous system (CNS) regions in the rat: spinal cord, cortex, hypothalamus, hippocampus, optic nerve, and cerebellum. The degree of fluorescence recovery (% recovery) and time constant of recovery (tau) served as quantitative indicators of coupling strength. Gap-junction coupling differed markedly between CNS regions. Coupling was weakest in astrocytes derived from spinal cord (43% recovery, tau approximately 400 s) and strongest in astrocytes from optic nerve (91% recovery, tau approximately 226 s) and cerebellum (95% recovery, tau approximately 100 s). As indicated by the degree of recovery, coupling strength among CNS regions could be ranked as follows: spinal cord < cortex < hypothalamus < hippocampus = optic nerve = cerebellum. Gap-junction coupling also differed between CNS regions with respect to its sensitivity to inhibition by the uncoupling agent octanol. Kd values for 50% inhibition by octanol ranged from 188 microM in spinal cord astrocytes to 654 microM in hippocampal astrocytes. Sensitivity of gap-junctions to octanol could be ranked as follows: spinal cord = cortex = hypothalamus > cerebellum > optic nerve > hippocampus. The observed differences in coupling indicate differences in the number of gap-junction connections in astrocytes cultured from the six CNS regions. These differences may reflect the adaptation of astrocytes to varying functional requirements in different CNS regions.

Connexin37 forms high conductance gap junction channels with subconductance state activity and selective dye and ionic permeabilities

Gap junctions are thought to mediate the direct intercellular coupling of adjacent cells by the open-closed gating of an aqueous pore permeable to ions and molecules of up to 1 kDa or 10-14 A in diameter. We symmetrically altered the ionic composition or asymmetrically added 6-carboxyfluorescein (6-CF, M(r) = 376), a fluorescent tracer, to pairs of connexin37-transfected mouse neuro2A cells to examine the ionic and dye permeability of human connexin37 channels. We demonstrate that the 300-pS channel formed by connexin37 has an effective relative anion/cation permeability ratio of 0.43, directly converts to at least one intermediate (63 pS) subconductance state, and that 6-CF dye transfer is accompanied by a 24% decrease in unitary channel conductance. These observations favor a new interpretation of the gap junction pore consistent with direct ion-channel interactions or electrostatic charge effects common to more conventional multistate ion channels. These results have distinct implications about the different forms of intercellular signaling (cationic, ionic, and/or biochemical) that can occur depending on the expression and conformation of the connexin channel proteins.

Regulation of gap junctional coupling in isolated pancreatic acinar cell pairs by cholecystokinin-octapeptide, vasoactive intestinal peptide (VIP) and a VIP-antagonist

Cholecystokinin-octapeptide (CCK-OP) induces a time- and dose-dependent decrease of gap junctional conductance in isolated pairs of pancreatic acinar cells. In double whole-cell experiments, the time course could be described by the latency and the half-life time (t1/2) of cell-to-cell uncoupling. The latency shows a biphasic dependence on [CCK-OP] with a minimum of about 50 sec at 10(-9) M CCK-OP. In the presence of vasoactive intestinal peptide (VIP), the biphasic relationship is shifted to lower CCK-OP concentrations. The increase of latency at high concentrations of CCK-OP (> 10(-9) M) was blocked by addition of a VIP-antagonist. t1/2 decreases monophasically with increasing [CCK-OP]. Addition of GTP gamma S to the pipette solution suppresses the [CCK-OP] dependence of the latency and potentiates the uncoupling phase. The kinetic data are discussed in terms of CCK binding to receptors of high and low affinity. Evidence is presented that secretion and cell-to-cell coupling are not related by an all-or-none process, but that for physiological CCK-OP concentrations, gap junctional uncoupling follows secretion.

Propranolol unmasks class III like electrophysiological properties of norepinephrine

Isolated perfused spontaneously beating rabbit hearts were treated with increasing concentrations of norepinephrine (0.01, 0.1, 0.5 mumol/l) either alone or in presence of propranolol (0.1 mumol/l). For analysis of the epicardial activation and repolarization process and epicardial mapping (256 unipolar leads) was performed. For each electrode the activation and repolarization time was determined. From these data the "breakthrough-points" (BTP) of epicardial activation were determined. At each electrode an activation vector (VEC) was calculated giving direction and velocity of the local excitation wave. The beat similarity of various heart beats (under NE) compared to control was evaluated by determination of the percentage of identical BTP and of similar VEC (deviation < or = 5 degrees). Moreover at each electrode the local activation recovery interval (ARI) and its standard deviation (of 256 leads, dispersion, DISP) were determined. Norepinephrine alone (0.01, 0.1, 0.5 mumol/l) led to an increase in left ventricular pressure, heart rate and DISP with concomitant frequency dependent reduction in ARI, and to changes in the epicardial activation pattern (reduction in BTP, VEC). We found that in the presence of propranolol (0.1 mumol/l) norepinephrine prolonged ARI and reduced ARI-dispersion. This effect was not due to changes in heart rate. The disturbing effects on the activation pattern were diminished. These effects could be prevented by pretreatment with 1 mumol/l prazosin. From these results we conclude, that norepinephrine prolongs the relative action potential duration via stimulation of alpha 1-adrenoceptor and enhances cellular coupling.(ABSTRACT TRUNCATED AT 250 WORDS)

Gap junctional connections between hair cells, supporting cells and nerves in a vestibular organ

The pattern of gap-junctional connections between cells in the vestibular neuroepithelium of the posterior semicircular duct of the alligator lizard are described based upon the study of freeze fracture replicas and ultrathin sections with a transmission electron microscope. Both type I and type II hair cells are coupled to adjacent supporting cells by a series of small macular gap junctions located in a ring around the hair cell at the level of the apical circumferential belt of actin filaments. Adjacent supporting cells are extensively interconnected by gap junctions. A few cases of gap junctions between afferent dendrites and supporting cells, and between afferent dendrites and calyceal nerve endings were seen. These morphological observations together with data from other studies in the literature suggest a possible role for supporting cells in altering the micromechanical properties of the hair cell receptor organs during stimulation.

Biophysical characterization of gap-junction channels in HeLa cells

HeLa cells seem not to be junctionally coupled when probed with techniques such as Lucifer yellow spreading and/or ionic coupling measured with three inserted microelectrodes. When investigated with double whole-cell patch-clamp measurements, HeLa cells in monolayer cultures were electrically coupled in 39% of the cases with very low transjunctional conductances (average one to five open channels). These gap-junction channels had a single-channel conductance gamma = 26 +/- 6 pS and were voltage-gated with an equivalent gating charge z = 3.1 +/- 1.5 for a voltage of half-maximal inactivation Uo = 49 +/- 10 mV. The voltage-dependent component represents only 31 +/- 8% of the total junctional conductance. The voltage-insensitive conductance is characterized by a residual open probability po (infinity) = 0.34 +/- 0.12, which corresponds to a ratio Gmin/Gmax = 0.50 +/- 0.12. Dissociation of monolayer cells into cell pairs yielded about 58% coupled cell pairs with no notably altered single-channel properties.

Dye and electric coupling between osteoblast-like cells in culture

Primary cultures of osteoblast-like cells (OB) derived from calvarial fragments of newborn rats and juvenile guinea pigs formed numerous gap junctions between neighboring cells in vitro. Intracellular injection of Lucifer yellow led to a staining of up to 30 adjacent cells. Parallel intracellular recordings showed that amplitudes of stimulated membrane potential changes (4-5 mV) were closely related between coupled cells. The coupling factor, which was derived from the ratio of these amplitudes, ranged between 0.1 and 0.8. The coupling factor (1) was not dependent on the membrane potential or the injected current strength; (2) strong acidosis (pH < 6.6) and hypercapnia (pCO2 > 80 mm Hg) did not affect electric or dye coupling; (3) elevation of intracellular cAMP level was ineffective; (4) rise of the extra- and intracellular Ca2+ concentration did not effect the electric coupling; (5) the anticonvulsant drugs carbamazepine and phenytoin impaired the coupling factor up to 59%. The findings show that cell-cell communication between OB via gap junctions proved stable under various conditions which, in other tissues, were found to reduce the coupling strength of gap junctions.

Temperature dependence of gap junction properties in neonatal rat heart cells

Cell pairs of neonatal rat hearts were used to study the influence of temperature on the electrical properties of gap junctions. A dual voltage-clamp method was adopted, which allowed the voltage gradient between the cells to be controlled and the intercellular current flow to be measured. Cell pairs with normal coupling revealed a positive correlation between the conductance of the junctional membranes, gj, and temperature. Cooling from 37 degrees C to 14 degrees C led to a steeper decrease in gj, cooling from 14 degrees C to -2 degrees C to a shallower decrease (37 degrees C: gj = 48.3 nS; 14 degrees C: gj = 21.4 nS; -2 degrees C: gj = 17.5 nS), corresponding to a temperature coefficient, Q10, of 1.43 and 1.14 respectively. The existence of two Q10 values implies that gj may be controlled by enzymatic reactions. When gj was low, i.e. below 5 nS (conditions: low temperature; treatment with 3 mM heptanol), it showed voltage-dependent gating. This property was not visible when gj was large, i.e. 20-70 nS (conditions: high temperature; normal saline), presumably because of series resistances (pipette resistance). Cell pairs with weak intrinsic coupling and normally coupled cell pairs treated with 3 mM heptanol revealed a positive correlation between the conductance of single gap-junction channels, gamma j, and temperature (37 degrees C: 75.6 pS; -2 degrees C: 19.6 pS), corresponding to a Q10 of 1.41.

Gap junctional conductance tunes phase difference of cholecystokinin evoked calcium oscillations in pairs of pancreatic acinar cells

Using the double whole-cell recording technique we measured the gap junctional conductance (gj), while simultaneously monitoring the cytoplasmic free calcium concentration ([Ca2+i]) in isolated acinar cell pairs from the pancreas of mouse. Physiological concentrations of the secretagogue cholecystokinin-octapeptide (CCK-OP) elicited [Ca2+i] oscillations and after a delay in the minute range reduced gj. The results provide the first evidence suggesting that gj regulates the phase difference (delta phi) of [Ca2+i] oscillations between neighbouring cells not in an all or none process, but with decreasing absolute value of gj delta phi monotonically increases. CCK-OP induced electrical uncoupling as well as the corresponding increase of delta phi could be blocked completely by the protein kinase C inhibitor polymyxin B. The data support the hypothesis that Ca2+ flow through gap junctions synchronizes [Ca2+i] oscillations between jap junctional coupled cells.

Serotonergic modulation of junctional conductance in an identified pair of neurons in the mollusc Lymnaea stagnalis

Serotonin (5-HT) is shown to modulate electrotonic coupling between two giant peptidergic neurons in the CNS of Lymnaea stagnalis. The primary effect of 5-HT appears to be a rapid and reversible decrease in gap junctional conductance.