Somatostatin increases voltage-dependent potassium currents in rat somatotrophs

1990 ◽  
Vol 259 (6) ◽  
pp. C854-C861 ◽  
Author(s):  
C. Chen ◽  
J. Zhang ◽  
J. D. Vincent ◽  
J. M. Israel
Keyword(s):  
Growth Hormone ◽  
Cell Voltage ◽  
Inhibitory Effect ◽  
Delayed Rectifier ◽  
Hormone Release ◽  
Growth Hormone Release ◽  
Voltage Dependent ◽  
Inward Currents ◽  
K Current ◽  
K Currents

To study the modulatory effects of somatostatin on membrane K+ currents, whole cell voltage-clamp recordings were performed on identified rat somatotrophs in primary culture. In the presence of Co2+ (2 mM) and tetrodotoxin (1 microM) in the bath solution to block Ca2+ and Na+ inward currents, two types of voltage-activated K+ currents were identified on the basis of their kinetics and pharmacology. First, a delayed rectifier K+ current (IK) had a threshold of -20 mV, did not decay during voltage steps lasting 300 ms, and was markedly attenuated by extracellular application of tetraethylammonium (TEA, 10 mM). Second, a transient outward K+ current (IA) was activated at -40 mV (from a holding potential of -80 mV) and persisted despite the presence of TEA. This IA was blocked by 4-aminopyridine (2 mM). Somatostatin (10 nM) increased IK by 75% and IA by 45% without obvious effects on steady-state voltage dependency of activation or inactivation, and these effects were reversible. This increase in K+ currents may contribute in part to the inhibitory effect of somatostatin on growth hormone release.

scholarly journals Voltage-dependent conductances in Limulus ventral photoreceptors.

1982 ◽  
Vol 79 (2) ◽  
pp. 187-209 ◽  
Author(s):  
J E Lisman ◽  
G L Fain ◽  
P M O'Day
Keyword(s):  
Outward Current ◽  
Delayed Rectifier ◽  
Molluscan Neurons ◽  
Inward Current ◽  
Transient Component ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Inward Currents ◽  
K Current ◽  
A Current

The voltage-dependent conductances of Limulus ventral photoreceptors have been investigated using a voltage-clamp technique. Depolarization in the dark induces inward and outward currents. The inward current is reduced by removing Na+ or Ca2+ and is abolished by removing both ions. These results suggest that both Na+ and Ca2+ carry voltage-dependent inward current. Inward current is insensitive to tetrodotoxin but is blocked by external Ni2+. The outward current has a large transient component that is followed by a smaller maintained component. Intracellular tetraethylammonium preferentially reduces the maintained component, and extracellular 4-amino pyridine preferentially reduces the transient component. Neither component is strongly affected by removal of extracellular Ca2+ or by intracellular injection of EGTA. It is concluded that the photoreceptors contain at least three separate voltage-dependent conductances: 1) a conductance giving rise to inward currents; 2) a delayed rectifier giving rise to maintained outward K+ current; and 3) a rapidly inactivating K+ conductance similar to the A current of molluscan neurons.

Blockade by lithium ions of potassium channels in rat anterior pituitary cells

1991 ◽  
Vol 261 (2) ◽  
pp. C218-C223 ◽  
Author(s):  
M. Kato ◽  
P. M. Lledo ◽  
J. D. Vincent
Keyword(s):  
Growth Hormone ◽  
Anterior Pituitary ◽  
Hormone Secretion ◽  
Male Rats ◽  
Delayed Rectifier ◽  
Pituitary Cells ◽  
Patch Clamp Technique ◽  
Anterior Pituitary Cells ◽  
K Current ◽  
K Currents

Extracellular Li+ has been known to facilitate the basal secretion of growth hormone from anterior pituitary cells and of catecholamine from chromaffin cells. In both cases, the intracellular accumulation of Li+ seems to be the prerequisite, and the presence of extracellular Ca2+ is indispensable. In this series of experiments, we examined whether Li+ blocked K+ currents by using primary cultured anterior pituitary cells from male rats. K+ currents were measured in the whole cell configuration of the patch-clamp technique. Extracellular Li+ (140 mM) suppressed both the delayed rectifier K+ current (IK) and the transient outward K+ current to 71 and 69% of control, respectively, in a reversible manner. IK elicited by a voltage step to +70 mV from holding potential of -70 mV was suppressed by 32.5 mM internal Li+ to 28% of control. Half-maximal suppression of K+ conductance by internal Li+ was 16 mM. Furthermore, Ca(2+)-channel blocker methoxyverapamil potently suppressed Li(+)-induced growth hormone secretion. From these results we propose that the blockade by Li+ of K+ channels could depolarize the cells and activate Ca2+ channels, thereby promoting the influx of Ca2+ and hormone secretion as a mechanism of Li(+)-induced hormone secretion.

Characterization of macroscopic outward currents of canine colonic myocytes

1989 ◽  
Vol 257 (3) ◽  
pp. C461-C469 ◽  
Author(s):  
W. C. Cole ◽  
K. M. Sanders
Keyword(s):  
Outward Current ◽  
Cell Voltage ◽  
Muscle Cells ◽  
Time Dependent ◽  
Delayed Rectifier ◽  
Delayed Rectifier Current ◽  
Outward Currents ◽  
Voltage Dependent ◽  
K Current ◽  
Time Courses

Outward currents of colonic smooth muscle cells were characterized by the whole cell voltage-clamp method. Four components of outward current were identified: a time-independent and three time-dependent components. The time-dependent current showed strong outward rectification positive to -25 mV and was blocked by tetraethylammonium. The time-dependent components were separated on the basis of their time courses, voltage dependence, and pharmacological sensitivities. They are as follows. 1) A Ca2+-activated K current sensitive to external Ca2+ and Ca2+ influx was blocked by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (0.1 X 10(-3) M) and nifedipine (1 X 10(-6) and was increased by elevated Ca2+ (8 X 10(-6) M) and BAY K 8644 (1 X 10(-6) M). 2) A "delayed rectifier" current was observed that decayed slowly with time and showed no voltage-dependent inactivation. 3) Spontaneous transient outward currents that were blocked by ryanodine (2 X 10(-6) M) were also recorded. The possible contributions of these currents to the electrical activity of colonic muscle cells in situ are discussed. Ca2+-activated K current may contribute a significant conductance to the repolarizing phase of electrical slow waves.

scholarly journals Voltage-dependent and odorant-regulated currents in isolated olfactory receptor neurons of the channel catfish.

1992 ◽  
Vol 99 (4) ◽  
pp. 505-529 ◽  
Author(s):  
T Miyamoto ◽  
D Restrepo ◽  
J H Teeter
Keyword(s):  
Action Potentials ◽  
Olfactory Receptor Neurons ◽  
Olfactory Neurons ◽  
Outward Currents ◽  
Na Currents ◽  
Voltage Dependent ◽  
Inward Currents ◽  
K Current ◽  
Receptor Neurons ◽  
K Currents

The electrical properties of olfactory receptor neurons, enzymatically dissociated from the channel catfish (Ictalurus punctatus), were studied using the whole-cell patch-clamp technique. Six voltage-dependent ionic currents were isolated. Transient inward currents (0.1-1.7 nA) were observed in response to depolarizing voltage steps from a holding potential of -80 mV in all neurons examined. They activated between -70 and -50 mV and were blocked by addition of 1 microM tetrodotoxin (TTX) to the bath or by replacing Na+ in the bath with N-methyl-D-glucamine and were classified as Na+ currents. Sustained inward currents, observed in most neurons examined when Na+ inward currents were blocked with TTX and outward currents were blocked by replacing K+ in the pipette solution with Cs+ and by addition of 10 mM Ba2+ to the bath, activated between -40 and -30 mV, reached a peak at 0 mV, and were blocked by 5 microM nimodipine. These currents were classified as L-type Ca2+ currents. Large, slowly activating outward currents that were blocked by simultaneous replacement of K+ in the pipette with Cs+ and addition of Ba2+ to the bath were observed in all olfactory neurons examined. The outward K+ currents activated over approximately the same range as the Na+ currents (-60 to -50 mV), but the Na+ currents were larger at the normal resting potential of the neurons (-45 +/- 11 mV, mean +/- SD, n = 52). Four different types of K+ currents could be differentiated: a Ca(2+)-activated K+ current, a transient K+ current, a delayed rectifier K+ current, and an inward rectifier K+ current. Spontaneous action potentials of varying amplitude were sometimes observed in the cell-attached recording configuration. Action potentials were not observed in whole-cell recordings with normal internal solution (K+ = 100 mM) in the pipette, but frequently appeared when K+ was reduced to 85 mM. These observations suggest that the membrane potential and action potential amplitude of catfish olfactory neurons are significantly affected by the activity of single channels due to the high input resistance (6.6 +/- 5.2 G omega, n = 20) and low membrane capacitance (2.1 +/- 1.1 pF, n = 46) of the cells.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Characterization of voltage- and Ca(2+)-activated K+ channels in squid olfactory receptor neurons.

1997 ◽  
Vol 200 (11) ◽  
pp. 1571-1586
Author(s):  
M T Lucero ◽  
N Chen
Keyword(s):  
Olfactory Receptor ◽  
Cell Voltage ◽  
Olfactory Receptor Neurons ◽  
Delayed Rectifier ◽  
Outward Currents ◽  
K Current ◽  
Receptor Neurons ◽  
Q10 Values ◽  
K Currents

We performed whole-cell voltage-clamp experiments on isolated olfactory neurons from the squid Lolliguncula brevis. Total outward currents were composed of three identifiable K+ currents: a delayed rectifier K+ current that showed slow inactivation and was sensitive to 5 mmol l-1 tetraethylammonium; a rapidly inactivating, 4-aminopyridine (4-AP)-sensitive, A-type K+ current and a Ca(2+)-sensitive K+ current that was blocked by 200 nmol l-1 charybdotoxin and 10 mmol l-1 Cd2+ but was insensitive to apamin. The proportion of each current type varied from cell to cell, suggesting that responses to a given odorant would depend of the complement of channels present. The kinetics of the K+ currents were affected by temperature, with Q10 values ranging from 2 to 6. The identification and characterization of these K+ currents will greatly aid our understanding of action potential generation in these cells and will facilitate modelling of how odor responses are transduced and coded in squid olfactory receptor neurons.

Inhibitory effect of galanin on growth hormone release from rat pituitary tumor cells (GH1) in culture

Life Sciences ◽  
1994 ◽  
Vol 55 (23) ◽  
pp. 1845-1851 ◽  
Author(s):  
Andrea Giustina ◽  
Carlo Bonfanti ◽  
Massimo Licini ◽  
Carmela De Rango ◽  
Gabriella Milani
Keyword(s):  
Growth Hormone ◽  
Tumor Cells ◽  
Pituitary Tumor ◽  
Inhibitory Effect ◽  
Hormone Release ◽  
Growth Hormone Release ◽  
Rat Pituitary ◽  
Rat Pituitary Tumor Cells

Inhibitory effect of somatostatin on dibutyryl cyclic AMP-induced insulin and growth hormone release in human subjects

Metabolism ◽  
1976 ◽  
Vol 25 (3) ◽  
pp. 321-328 ◽  
Author(s):  
M. Peracchi ◽  
E. Reschini ◽  
L. Cantalamessa ◽  
A. Catania ◽  
G. Giustina
Keyword(s):  
Growth Hormone ◽  
Cyclic Amp ◽  
Human Subjects ◽  
Inhibitory Effect ◽  
Hormone Release ◽  
Growth Hormone Release ◽  
Dibutyryl Cyclic Amp

INHIBITORY EFFECT OF CIMETIDINE ON L-DOPA-STIMULATED GROWTH HORMONE RELEASE IN NORMAL MAN

1984 ◽  
Vol 21 (5) ◽  
pp. 535-540 ◽  
Author(s):  
A. ZANOBONI ◽  
G. GALMOZZI ◽  
S. MARINONI ◽  
WANDA ZANOBONI-MUCIACCIA
Keyword(s):  
Growth Hormone ◽  
Inhibitory Effect ◽  
Hormone Release ◽  
Growth Hormone Release ◽  
Normal Man

scholarly journals Ionic currents and ion channels of lobster olfactory receptor neurons.

1989 ◽  
Vol 94 (6) ◽  
pp. 1085-1099 ◽  
Author(s):  
T S McClintock ◽  
B W Ache
Keyword(s):  
Ion Channels ◽  
Olfactory Receptor ◽  
Ionic Currents ◽  
K Channel ◽  
Delayed Rectifier ◽  
Na Current ◽  
Cl Channel ◽  
Inward Currents ◽  
K Current ◽  
K Currents

The role of the soma of spiny lobster olfactory receptor cells in generating odor-evoked electrical signals was investigated by studying the ion channels and macroscopic currents of the soma. Four ionic currents; a tetrodotoxin-sensitive Na+ current, a Ca++ current, a Ca(++)-activated K+ current, and a delayed rectifier K+ current, were isolated by application of specific blocking agents. The Na+ and Ca++ currents began to activate at -40 to -30 mV, while the K+ currents began to activate at -30 to -20 mV. The size of the Na+ current was related to the presence of a remnant of a neurite, presumably an axon, and not to the size of the soma. No voltage-dependent inward currents were observed at potentials below those activating the Na+ current, suggesting that receptor potentials spread passively through the soma to generate action potentials in the axon of this cell. Steady-state inactivation of the Na+ current was half-maximal at -40 mV. Recovery from inactivation was a single exponential function that was half-maximal at 1.7 ms at room temperature. The K+ currents were much larger than the inward currents and probably underlie the outward rectification observed in this cell. The delayed rectifier K+ current was reduced by GTP-gamma-S and AIF-4, agents which activate GTP-binding proteins. The channels described were a 215-pS Ca(++)-activated K+ channel, a 9.7-pS delayed rectifier K+ channel, and a 35-pS voltage-independent Cl- channel. The Cl- channel provides a constant leak conductance that may be important in stabilizing the membrane potential of the cell.

A fast transient potassium current in thalamic relay neurons: kinetics of activation and inactivation

1991 ◽  
Vol 66 (4) ◽  
pp. 1304-1315 ◽  
Author(s):  
J. R. Huguenard ◽  
D. A. Coulter ◽  
D. A. Prince
Keyword(s):  
Steady State ◽  
Reversal Potential ◽  
Cell Voltage ◽  
Inactivation Kinetics ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
K Current ◽  
K Currents ◽  
Relay Neurons

1. Whole-cell voltage-clamp techniques were used to record K+ currents in relay neurons (RNs) that had been acutely isolated from rat thalamic ventrobasal complex and maintained at 23 degrees C in vitro. Tetrodoxin (TTX; 0.5 microM) was used to block Na+ currents, and reduced extracellular levels of Ca2+ (1 mM) were used to minimize contributions from Ca2+ current (ICa). 2. In RNs, depolarizing commands activate K+ currents characterized by a substantial rapidly inactivating (time constant approximately 20 ms) component, the features of which correspond to those of the transient K+ current (IA) in other preparations, and by a smaller, more slowly activating K+ current, "IK". IA was reversibly blocked by 4-aminopyridine (4-AP, 5 mM), and the reversal potential varied with [K+]o as predicted by the Nernst equation. 3. IA was relatively insensitive to blockade by tetraethylammonium [TEA; 50%-inhibitory concentration (IC50) much much greater than 20 mM]; however, two components of IK were blocked with IC50S of 30 microM and 3 mM. Because 20 mM TEA blocked 90% of the sustained current while reducing IA by less than 10%, this concentration was routinely used in experiments in which IA was isolated and characterized. To further minimize contamination by other conductances, 4-AP was added to TEA-containing solutions and the 4-AP-sensitive current was obtained by subtraction. 4. Voltage-dependent steady-state inactivation of peak IA was described by a Boltzman function with a slope factor (k) of -6.5 and half-inactivation (V1/2) occurring at -75 mV. Activation of IA was characterized by a Boltzman curve with V1/2 = -35 mV and k = 10.8. 5. IA activation and inactivation kinetics were best fitted by the Hodgkin-Huxley m4h formalism. The rate of activation was voltage dependent, with tau m decreasing from 2.3 ms at -40 mV to 0.5 ms at +50 mV. Inactivation was relatively voltage independent and nonexponential. The rate of inactivation was described by two exponential decay processes with time constants (tau h1 and tau h2) of 20 and 60 ms. Both components were steady-state inactivated with similar voltage dependence. 6. Temperature increases within the range of 23-35 degrees C caused IA activation and inactivation rates to become faster, with temperature coefficient (Q10) values averaging 2.8. IA amplitude also increased as a function of temperature, albeit with a somewhat lower Q10 of 1.6. 7. Several voltage-dependent properties of IA closely resemble those of the transient inward Ca2+ current, IT. (ABSTRACT TRUNCATED AT 400 WORDS)

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