Cellular calcium regulates outward currents in rabbit intestinal smooth muscle cell

1987 ◽  
Vol 252 (4) ◽  
pp. C401-C410 ◽  
Author(s):  
Y. Ohya ◽  
K. Kitamura ◽  
H. Kuriyama
Keyword(s):  
Smooth Muscle ◽  
Outward Current ◽  
Muscle Layer ◽  
Transient Outward Current ◽  
Physiological Salt Solution ◽  
Rabbit Ileum ◽  
Longitudinal Muscle Layer ◽  
Outward Currents ◽  
Bath Application ◽  
Sustained Outward Current

The nature of transient and oscillatory outward currents (ITO and IOO) in fragmented smooth muscle cells (smooth muscle ball, SMB) from the longitudinal muscle layer of the rabbit ileum, was studied using a single electrode voltage clamp technique. With a high K+ solution containing 0.3 mM ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA) in the pipette and physiological salt solution (PSS) in the bath, the Ca inward current was followed by a large transient outward current (ITO) and spontaneous oscillations of the outward current (IOO) on the sustained outward current (ISO) were elicited by a depolarizing pulse, positive to -30 mV (holding potential of -60 mV). When the internal fluid of the SMB was replaced with Cs+-tetraethylammonium+ (TEA+) solution, or when the concentration of EGTA in the pipette was increased to 4 mM, using the intracellular perfusion technique, both ITO and IOO were abolished. In Mn2+ solution both currents were also inhibited. Bath application of TEA+, procaine or A23187 completely blocked both ITO and IOO. Caffeine (0.3-1 mM) enhanced the amplitude of ITO and generations of IOO, and concentrations of caffeine over 3 mM transiently enhanced, but finally suppressed both these currents. These results suggest that the generation of ITO is closely related to the Ca2+ influx, whereas the generation of IOO may be initiated by an increment in the intracellular concentration of Ca2+, possibly released from store sites.

Membrane currents recorded from a fragment of rabbit intestinal smooth muscle cell

1986 ◽  
Vol 251 (3) ◽  
pp. C335-C346 ◽  
Author(s):  
Y. Ohya ◽  
K. Terada ◽  
K. Kitamura ◽  
H. Kuriyama
Keyword(s):  
Smooth Muscle ◽  
Longitudinal Muscle ◽  
Outward Current ◽  
Ionic Currents ◽  
Muscle Layer ◽  
Dependent Manner ◽  
Rabbit Ileum ◽  
Longitudinal Muscle Layer ◽  
Inward Current ◽  
K Currents

Properties of ionic currents in smooth muscle membranes of the longitudinal muscle layer of the rabbit ileum were investigated using the single electrode voltage clamp method. In the present experiments, this method was applicable only to the smooth muscle ball (fragment) and not for the dispersed whole cell, because of incompleteness of the voltage clamping. A voltage step elicited a transient inward current followed by an outward current. This outward current was partly inhibited by Mn2+ or nisoldipine or by a reduction in the extracellular [Ca2+] ([Ca2+]o). Tetraethylammonium (TEA) reduced the delayed outward current in a dose-dependent manner, but 50 mM TEA did not produce a complete block of a residual current. When the pipette contained K+-free (Cs+ with TEA+) solution, the residual outward current was abolished. The inward current was elicited at -30 mV (holding potential of -60 mV) and reached the maximal value at +10 mV; the polarity was reversed at +60 mV. This inward current depended on the [Ca2+]o and was blocked by Mn2+ or nisoldipine. Ba2+ also permeated the membrane, and the inward current evoked by Ba2+ was also blocked by Mn2+ or nisoldipine. Reduction of [Na+]o in a solution containing 2.4 mM Ca2+ neither modified the current-voltage relation nor the decay of the inward current, but when [Ca2+]o was reduced to below 1 microM, Na+ permeated the membrane and was blocked by nisoldipine. In conclusion, ionic currents were recordable from the fragmented ball of the longitudinal muscle of rabbit ileum. There were at least two K+ currents as the outward current (Ca2+-dependent K+ and delayed K+ currents) and a Ca2+ current as the inward current. The property of the Ca2+ channel was similar to that observed with other preparations.

Ca2+ sparks and BK currents in gallbladder myocytes: role in CCK-induced response

2002 ◽  
Vol 282 (1) ◽  
pp. G165-G174 ◽  
Author(s):  
María J. Pozo ◽  
Guillermo J. Pérez ◽  
Mark T. Nelson ◽  
Gary M. Mawe
Keyword(s):  
Smooth Muscle ◽  
Ryanodine Receptor ◽  
Outward Current ◽  
Bk Channels ◽  
Transient Outward Current ◽  
Induced Response ◽  
Current Clamp ◽  
Current Activity ◽  
Outward Currents ◽  
Current Clamp Mode

We sought to elucidate the regulation of gallbladder smooth muscle (GBSM) excitability by localized Ca2+ release events (sparks) and large-conductance Ca2+-dependent (BK) channels by determining whether sparks exist in GBSM and, if so, whether they activate BK channels. Sparks were identified in isolated GBSM loaded with fluo 4. Each spark was associated with a transient outward current, suggesting communication of ryanodine receptor (RyR) channels with BK channels. This was confirmed by the inhibition of outward currents with iberiotoxin (100 nM), thapsigargin (200 nM), and ryanodine (10 μM). In current clamp mode, the transient BK currents were associated with brief membrane hyperpolarizations (10.9 ± 1.3 mV). Because transient BK currents could dampen GBSM excitability, we tested whether CCK attenuates these events. CCK (10 nM) reduced the amplitude and frequency of transient BK currents, and subsequent caffeine application restored transient BK current activity. These results support the concept that RyRs and BK channels contribute to the regulation of GBSM excitability and that CCK can act in part by inhibiting this pathway.

Postnatal rat nigrostriatal dopaminergic neurons exhibit five types of potassium conductances

1990 ◽  
Vol 64 (1) ◽  
pp. 262-272 ◽  
Author(s):  
N. L. Silva ◽  
C. M. Pechura ◽  
J. L. Barker
Keyword(s):  
Action Potential ◽  
Outward Current ◽  
Transient Outward Current ◽  
Channel Blockers ◽  
Current Response ◽  
Whole Cell Patch Clamp ◽  
Outward Currents ◽  
Potassium Conductances ◽  
Steady State Inactivation ◽  
Sustained Outward Current

1. We have investigated the electrical properties of neurons acutely dissociated from the substantia nigra zona compacta (SNZC) of the postnatal rat with whole cell patch-clamp recordings. Retrogradely labeled nigrostriatal neurons were identified with the use of rhodamine-labeled fluorescent latex microspheres. Over 90% of the rhodamine-labeled neurons in the SNZC demonstrated formaldehyde/glutaraldehyde-induced catecholamine fluorescence, indicating that they were dopaminergic (DA) neurons. 2. DA neurons had 15-20 microns ovoid or fusiform-shaped cell bodies with 2-3 thick proximal processes. Labeled neurons generated spontaneous action-potential activity in both regular and irregular patterns. These cells exhibited input resistances of 300-600 M omega and action-potential amplitudes of 60-80 mV. Locally applied dopamine inhibited the spontaneous activity of these neurons by hyperpolarizing the cells. 3. Outward currents were examined with voltage-clamp recordings using a tetrodotoxin (TTX)-containing medium. In all DA cells, depolarizing voltage commands activated several components of outward current depending on the holding potential of the cell. When cells were held at -40 mV (or more positive), voltage steps activated a sustained outward current. If the membrane potential was held more negative than -50 mV, a rapidly activating and inactivating component of outward current response could also be detected. 4. From a hyperpolarized holding potential (-90 mV) the transient outward current activated with depolarizing commands to -55 mV, peaking within 5 ms. The current inactivated with a monoexponential time constant of 53 +/- 4 (SE) ms. At more positive holding potentials (-40 mV) the steady-state inactivation of the current could be removed by applying a conditioning hyperpolarizing prepulse. In response to a fixed depolarizing voltage step, half-maximal inactivation occurred at about -65 mV. The transient current was blocked by 4-aminopyridine (4-AP). 5. The sustained outward currents were isolated by holding the cells at -40 mV. Two components of sustained outward current were distinguished by their sensitivity to the calcium channel blockers Co2+ (5 mM) and/or Cd2+ (200 microM). The current remaining in the presence of Co2+/Cd2+ was activated by depolarizing voltage commands more positive than -40 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

Nitric oxide mediates outward potassium currents in opossum esophageal circular smooth muscle

1996 ◽  
Vol 270 (6) ◽  
pp. G932-G938 ◽  
Author(s):  
J. Jury ◽  
K. R. Boev ◽  
E. E. Daniel
Keyword(s):  
Nitric Oxide ◽  
Smooth Muscle ◽  
Circular Muscle ◽  
Outward Current ◽  
Equilibrium Potential ◽  
Patch Clamp Technique ◽  
Pipette Solution ◽  
Whole Cell ◽  
Circular Smooth Muscle ◽  
Outward Currents

Single smooth muscle cells from the opossum body circular muscle were isolated and whole cell currents were characterized by the whole cell patch-clamp technique. When the cells were held at -50 mV and depolarized to 70 mV in 20-mV increments, initial small inactivating inward currents were evoked (-30 to 30 mV) followed by larger sustained outward currents. Depolarization from a holding potential of -90 mV evoked an initial fast inactivating outward current sensitive to 4-aminopyridine but not to high levels of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). The outward currents reversed near K+ equilibrium potential and were abolished when KCl was replaced by CsCl in the pipette solution. The sustained outward current was inhibited by quinine and cesium. High EGTA in the pipette solution reduced but did not abolish the sustained outward currents, suggesting that both Ca(2+)-dependent and -independent currents were evoked. The nitric oxide (NO)-releasing agents Sin-1 and sodium nitroprusside increased outward K+ currents. High levels of EGTA in the pipette solution abolished the increase in outward current induced by Sin-1. The presence of cyclopiazonic acid, an inhibitor of the sarcoplasmic reticulum (SR) Ca2+ pump, blocked the effects of NO-releasing agents. We conclude that NO release activates K+ outward currents in opossum esophagus circular muscle, which may depend on Ca2+ release from the SR stores.

scholarly journals Small-conductance Ca2+-dependent K+ channels activated by ATP in murine colonic smooth muscle

1997 ◽  
Vol 273 (6) ◽  
pp. C2010-C2021 ◽  
Author(s):  
S. D. Koh ◽  
G. M. Dick ◽  
K. M. Sanders
Keyword(s):  
Smooth Muscle ◽  
Pyridoxal Phosphate ◽  
Single Channel ◽  
Outward Current ◽  
Disulfonic Acid ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Outward Currents ◽  
Murine Colon ◽  
Small Conductance

The patch-clamp technique was used to determine the ionic conductances activated by ATP in murine colonic smooth muscle cells. Extracellular ATP, UTP, and 2-methylthioadenosine 5′-triphosphate (2-MeS-ATP) increased outward currents in cells with amphotericin B-perforated patches. ATP (0.5–1 mM) did not affect whole cell currents of cells dialyzed with solutions containing ethylene glycol-bis(β-aminoethyl ether)- N, N, N′, N′-tetraacetic acid. Apamin (3 × 10−7M) reduced the outward current activated by ATP by 32 ± 5%. Single channel recordings from cell-attached patches showed that ATP, UTP, and 2-MeS-ATP increased the open probability of small-conductance, Ca2+-dependent K+ channels with a slope conductance of 5.3 ± 0.02 pS. Caffeine (500 μM) enhanced the open probability of the small-conductance K+ channels, and ATP had no effect after caffeine. Pyridoxal phosphate 6-azophenyl-2′,4′-disulfonic acid tetrasodium (PPADS, 10−4 M), a nonselective P2 receptor antagonist, prevented the increase in open probability caused by ATP and 2-MeS-ATP. PPADS had no effect on the response to caffeine. ATP-induced hyperpolarization in the murine colon may be mediated by P2y-induced release of Ca2+ from intracellular stores and activation of the 5.3-pS Ca2+-activated K+ channels.

Differences in outward currents between neonatal and adult rabbit ventricular cells

1994 ◽  
Vol 266 (3) ◽  
pp. H1184-H1194 ◽  
Author(s):  
J. Sanchez-Chapula ◽  
A. Elizalde ◽  
R. Navarro-Polanco ◽  
H. Barajas
Keyword(s):  
Action Potential ◽  
Papillary Muscle ◽  
Action Potential Duration ◽  
Outward Current ◽  
Stimulation Frequency ◽  
Transient Outward Current ◽  
Adult Rabbit ◽  
Outward Currents ◽  
Recovery From Inactivation ◽  
In Cells

In adult rabbit ventricular preparations, action potential duration is significantly increased when stimulation frequency is increased from 0.1 to 1.0 Hz. In neonatal preparations, a similar change in stimulation frequency produced no significant increase in action potential duration. To identify the ionic basis for this difference, we studied different outward currents in single myocytes from papillary muscle and from epicardial tissue of adult and neonatal rabbits. The densities of the outward currents in neonatal cells were about one-half of the current density in adult cells. The density of the voltage-activated transient outward current (I(to1)) was smaller in cells from papillary muscle than in cells from epicardium in adult and newborn rabbits. We found major differences in the kinetic behavior of I(to1) between adult and neonatal cells: 1) the rate of apparent inactivation was faster in neonatal cells, and 2) the recovery from inactivation was significantly faster in neonatal cells, with a time constant of 113 vs. 1,356 ms. We propose that this marked difference in the recovery from inactivation of I(to1) is the basis for the difference in frequency dependence of action potential duration.

Transient potassium currents in avian sensory neurons

1990 ◽  
Vol 63 (4) ◽  
pp. 725-737 ◽  
Author(s):  
S. K. Florio ◽  
C. D. Westbrook ◽  
M. R. Vasko ◽  
R. J. Bauer ◽  
J. L. Kenyon
Keyword(s):  
Single Channel ◽  
Outward Current ◽  
Potassium Currents ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Single Channels ◽  
Patch Clamp Technique ◽  
Small Component ◽  
Whole Cell ◽  
Outward Currents

1. We used the patch-clamp technique to study voltage-activated transient potassium currents in freshly dispersed and cultured chick dorsal root ganglion (DRG) cells. Whole-cell and cell-attached patch currents were recorded under conditions appropriate for recording potassium currents. 2. In whole-cell experiments, 100-ms depolarizations from normal resting potentials (-50 to -70 mV) elicited sustained outward currents that inactivated over a time scale of seconds. We attribute this behavior to a component of delayed rectifier current. After conditioning hyperpolarizations to potentials negative to -80 mV, depolarizations elicited transient outward current components that inactivated with time constants in the range of 8-26 ms. We attribute this behavior to a transient outward current component. 3. Conditioning hyperpolarizations increased the rate of activation of the net outward current implying that the removal of inactivation of the transient outward current allows it to contribute to early outward current during depolarizations from negative potentials. 4. Transient current was more prominent on the day the cells were dispersed and decreased with time in culture. 5. In cell-attached patches, single channels mediating outward currents were observed that were inactive at resting potentials but were active transiently during depolarizations to potentials positive to -30 mV. The probability of channels being open increased rapidly (peaking within approximately 6 ms) and then declined with a time constant in the range of 13-30 ms. With sodium as the main extracellular cation, single-channel conductances ranged from 18 to 32 pS. With potassium as the main extracellular cation, the single-channel conductance was approximately 43 pS, and the channel current reversed near 0 mV, as expected for a potassium current. 6. We conclude that the transient potassium channels mediate the component of transient outward current seen in the whole-cell experiments. This current is a relatively small component of the net current during depolarizations from normal resting potentials, but it can contribute significant outward current early in depolarizations from hyperpolarized potentials.

In vitro microelectrode study of the electrical properties of smooth muscle in equine ileum

2001 ◽  
Vol 149 (23) ◽  
pp. 707-711 ◽  
Author(s):  
N. P. H. Hudson ◽  
I. G. Mayhew ◽  
G. T. Pearson
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Smooth Muscle Cells ◽  
Longitudinal Muscle ◽  
Muscle Cells ◽  
Muscle Layer ◽  
Potential Oscillations ◽  
Longitudinal Muscle Layer ◽  
Membrane Potential Oscillations

Intracellular microelectrode recordings were made from smooth muscle cells in cross-sectional preparations of equine ileum, superfused in vitro. Membrane potential oscillations and spike potentials were recorded in all preparations, but recordings were made more readily from cells in the longitudinal muscle layer than from cells in the circular layer. The mean (se) resting membrane potential (RMP) of smooth muscle cells in the longitudinal muscle layer was -51.9 (1.2) mV, and the membrane potential oscillations in this layer had a mean amplitude of 4.8 (0.4) mV, a frequency of 9.0 (0.1) cycles per minute and a duration of 5.8 (0.2) seconds. The membrane potential oscillations were preserved in the presence of tetrodotoxin. A waxing and waning pattern of membrane potential oscillation activity was observed. Nifedipine abolished the spiking contractile activity of the smooth muscle, did not abolish the membrane potential oscillations but did alter their temporal characteristics.

Sarcoplasmic Reticulum Function in Smooth Muscle

2010 ◽  
Vol 90 (1) ◽  
pp. 113-178 ◽  
Author(s):  
Susan Wray ◽  
Theodor Burdyga
Keyword(s):  
Smooth Muscle ◽  
Sarcoplasmic Reticulum ◽  
Physiological Activity ◽  
Smooth Muscles ◽  
Outward Current ◽  
Integrated Approach ◽  
Transient Outward Current ◽  
Coupling Mechanism ◽  
Striated Muscles ◽  
Development And Aging

The sarcoplasmic reticulum (SR) of smooth muscles presents many intriguing facets and questions concerning its roles, especially as these change with development, disease, and modulation of physiological activity. The SR's function was originally perceived to be synthetic and then that of a Ca store for the contractile proteins, acting as a Ca amplification mechanism as it does in striated muscles. Gradually, as investigators have struggled to find a convincing role for Ca-induced Ca release in many smooth muscles, a role in controlling excitability has emerged. This is the Ca spark/spontaneous transient outward current coupling mechanism which reduces excitability and limits contraction. Release of SR Ca occurs in response to inositol 1,4,5-trisphosphate, Ca, and nicotinic acid adenine dinucleotide phosphate, and depletion of SR Ca can initiate Ca entry, the mechanism of which is being investigated but seems to involve Stim and Orai as found in nonexcitable cells. The contribution of the elemental Ca signals from the SR, sparks and puffs, to global Ca signals, i.e., Ca waves and oscillations, is becoming clearer but is far from established. The dynamics of SR Ca release and uptake mechanisms are reviewed along with the control of luminal Ca. We review the growing list of the SR's functions that still includes Ca storage, contraction, and relaxation but has been expanded to encompass Ca homeostasis, generating local and global Ca signals, and contributing to cellular microdomains and signaling in other organelles, including mitochondria, lysosomes, and the nucleus. For an integrated approach, a review of aspects of the SR in health and disease and during development and aging are also included. While the sheer versatility of smooth muscle makes it foolish to have a “one model fits all” approach to this subject, we have tried to synthesize conclusions wherever possible.

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