scholarly journals On the origin of rhythmic calcium transients in the ICC-MP of the mouse small intestine

2011 ◽  
Vol 301 (5) ◽  
pp. G835-G845 ◽  
Author(s):  
Bobbi-Jo Lowie ◽  
Xuan-Yu Wang ◽  
Elizabeth J. White ◽  
Jan D. Huizinga
Keyword(s):  
Small Intestine ◽  
Calcium Channel ◽  
Calcium Release ◽  
Imaging Study ◽  
Cyclopiazonic Acid ◽  
Calcium Oscillations ◽  
Calcium Transients ◽  
Pacemaker Activity ◽  
Type I ◽  
Endoplasmic Reticulum Calcium

Interstitial cells of Cajal associated with the myenteric plexus (ICC-MP) are pacemaker cells of the small intestine, producing the characteristic omnipresent electrical slow waves, which orchestrate peristaltic motor activity and are associated with rhythmic intracellular calcium oscillations. Our objective was to elucidate the origins of the calcium transients. We hypothesized that calcium oscillations in the ICC-MP are primarily regulated by the sarcoplasmic reticulum (SR) calcium release system. With the use of calcium imaging, study of the effect of T-type calcium channel blocker mibefradil revealed that T-type channels did not play a major role in generating the calcium transients. 2-Aminoethoxydiphenyl borate, an inositol 1,4,5 trisphosphate receptor (IP3R) inhibitor, and U73122, a phospholipase C inhibitor, both drastically decreased the frequency of calcium oscillations, suggesting a major role of IP3 and IP3-induced calcium release from the SR. Immunohistochemistry proved the expression of IP3R type I (IP3R-I), but not type II (IP3R-II) and type III (IP3R-III) in ICC-MP, indicating the involvement of the IP3R-I subtype in calcium release from the SR. Cyclopiazonic acid, a SR/endoplasmic reticulum calcium ATPase pump inhibitor, strongly reduced or abolished calcium oscillations. The Na-Ca exchanger (NCX) in reverse mode is likely involved in refilling the SR because the NCX inhibitor KB-R7943 markedly reduced the frequency of calcium oscillations. Immunohistochemistry revealed 100% colocalization of NCX and c-Kit in ICC-MP. Testing a mitochondrial NCX inhibitor, we were unable to show an essential role for mitochondria in regulating calcium oscillations in the ICC-MP. In summary, ongoing IP3 synthesis and IP3-induced calcium release from the SR, via the IP3R-I, are the major drivers of the calcium transients associated with ICC pacemaker activity. This suggests that a biochemical clock intrinsic to ICC determines the pacemaker frequency, which is likely directly linked to kinetics of the IP3-activated SR calcium channel and IP3 metabolism.

Mechanisms Underlying Type I mGluR-Induced Activation of Lobster Gastric Mill Neurons

2006 ◽  
Vol 96 (6) ◽  
pp. 3378-3388 ◽  
Author(s):  
Rafael Levi ◽  
Allen I. Selverston
Keyword(s):  
G Protein ◽  
Calcium Release ◽  
Metabotropic Glutamate Receptor ◽  
Cyclopiazonic Acid ◽  
Stomatogastric Ganglion ◽  
Type I ◽  
Gastric Mill ◽  
Concentration Increase ◽  
Cellular Mechanisms ◽  
Excitatory Effect

In addition to ionotropic effects, glutamate and acetylcholine have metabotropic modulatory effects on many neurons. Here we show that in the stomatogastric ganglion of the lobster, glutamate, one of the main ionotropic neurotransmitters, modulates the excitability of gastric mill neurons. The neurons in this well-studied system produce rhythmic output to a subset of lobster foregut muscles. Recently, metabotropic glutamate receptor (mGluR) agonists were suggested as modulators of the rhythmic output, in addition to the previously described muscarinic modulation by acetylcholine. However, the cellular mechanisms responsible for these effects on the pattern are not known. Using intracellular recording methods and calcium imaging, we show that glutamate has an excitatory effect on specific neurons in the stomatogastric ganglion, which is mediated by mGluRs. Responses to the application of mGluR type I agonists are transient oscillations in the system, probably arising from network interactions. We show that the excitatory effect is sensitive to phospholipase-C and IP3 and is G-protein dependent. The G-protein dependency was demonstrated by GDPβS and GTPγS injection into identified neurons. The depolarizations and oscillations were accompanied by an increase of intracellular Ca2+ levels and correlated Ca2+ oscillations. By using cyclopiazonic acid, an endoreticular Ca2+ uptake inhibitor, we show that some internal calcium release may augment the response, but is not crucial for its production. Interestingly, although Ca2+ concentration increase is typically associated with the phosphoinositide pathway, in the lobster, the Ca2+ concentration increase—either voltage dependent or independent—cannot account for the observed depolarization.

scholarly journals Spatiotemporal properties of high-speed calcium oscillations in the pedunculopontine nucleus

2013 ◽  
Vol 115 (9) ◽  
pp. 1402-1414 ◽  
Author(s):  
James Hyde ◽  
Nebojsa Kezunovic ◽  
Francisco J. Urbano ◽  
Edgar Garcia-Rill
Keyword(s):  
Calcium Channel ◽  
Calcium Channel Blocker ◽  
High Speed ◽  
Channel Blocker ◽  
Stokes Shift ◽  
Dendritic Tree ◽  
Pedunculopontine Nucleus ◽  
Gamma Oscillations ◽  
Calcium Oscillations ◽  
Calcium Transients

The pedunculopontine nucleus (PPN) is a component of the reticular activating system (RAS), and is involved in the activated states of waking and rapid eye movement (REM) sleep. Gamma oscillations (approximately 30–80 Hz) are evident in all PPN neurons and are mediated by high-threshold voltage-dependent N- and P/Q-type calcium channels. We tested the hypothesis that high-speed calcium imaging would reveal calcium-mediated oscillations in dendritic compartments in synchrony with patch-clamp recorded oscillations during depolarizing current ramps. Patch-clamped 8- to 16-day-old rat PPN neurons ( n = 67 out of 121) were filled with Fura 2, Bis Fura, or OGB1/CHR. This study also characterized a novel ratiometric technique using Oregon Green BAPTA-1 (OGB1) with coinjections of a new long-stokes-shift dye, Chromeo 494 (CHR). Fluorescent calcium transients were blocked with the nonspecific calcium channel blocker cadmium, or by the combination of ω-agatoxin-IVA, a specific P/Q-type calcium channel blocker, and ω-conotoxin-GVIA, a specific N-type calcium channel blocker. The calcium transients were evident in different dendrites (suggesting channels are present throughout the dendritic tree) along the sampled length without interruption (suggesting channels are evenly distributed), and appeared to represent a summation of oscillations present in the soma. We confirm that PPN calcium channel-mediated oscillations are due to P/Q- and N-type channels, and reveal that these channels are distributed along the dendrites of PPN cells.

Generation of slow wave type action potentials in the mouse small intestine involves a non-L-type calcium channel

1995 ◽  
Vol 73 (10) ◽  
pp. 1502-1511 ◽  
Author(s):  
John Malysz ◽  
David Richardsons ◽  
Laura Farraway ◽  
Jan D. Huizinga ◽  
Marie-Odile Christen
Keyword(s):  
Small Intestine ◽  
Calcium Channel ◽  
Slow Wave ◽  
Calcium Channel Blockers ◽  
Action Potentials ◽  
Slow Waves ◽  
Pacemaker Activity ◽  
Channel Blockers ◽  
Wave Type ◽  
Mouse Small Intestine

Intrinsic electrical activities in various isolated segments of the mouse small intestine were recorded (i) to characterize action potential generation and (ii) to obtain a profile on the ion channels involved in initiating the slow wave type action potentials (slow waves). Gradients in slow wave frequency, resting membrane potential, and occurrence of spiking activity were found, with the proximal intestine exhibiting the highest frequency, the most hyperpolarized cell membrane, and the greatest occurrence of spikes. The slow waves were only partially sensitive to L-type calcium channel blockers. Nifedipine, verapamil, and pinaverium bromide abolished spikes that occurred on the plateau phase of the slow waves in all tissues. The activity that remained in the presence of L-type calcium channel blockers, the upstroke potential, retained a similar amplitude to the original slow wave and was of identical frequency. The upstroke potential was not sensitive to a reduction in extracellular chloride or to the sodium channel blockers tetrodotoxin and mexiletine. Abolishment of the Na+ gradient by removal of 120 mM extracellular Na+ reduced the upstroke potential frequency by 13–18% and its amplitude by 50–70% in the ileum. The amplitude was similarly reduced by Ni2+ (up to 5 mM), and by flufenamic acid (100 μM), a nonspecific cation and chloride channel blocker. Gadolinium, a nonspecific blocker of cation and stretch-activated channels, had no effect. Throughout these pharmacological manipulations, a robust oscillation remained at 5–10 mV. This oscillation likely reflects pacemaker activity. It was rapidly abolished by removal of extracellular calcium but not affected by L-type calcium channel blockers. In summary, the mouse small intestine has been established as a model for research into slow wave generation and electrical pacemaker activity. The upstroke part of the slow wave has two components, the pacemaker component involves a non-L-type calcium channel.Key words: slow wave, pacemaker, calcium channel, pinaverium, smooth muscle.

scholarly journals Relationship of calcium transients to calcium currents and charge movements in myotubes expressing skeletal and cardiac dihydropyridine receptors.

1994 ◽  
Vol 103 (1) ◽  
pp. 125-147 ◽  
Author(s):  
J García ◽  
T Tanabe ◽  
K G Beam
Keyword(s):  
Skeletal Muscle ◽  
Calcium Channel ◽  
Calcium Current ◽  
Calcium Release ◽  
Voltage Dependence ◽  
Calcium Transient ◽  
Calcium Currents ◽  
Calcium Transients ◽  
Charge Movement ◽  
The Relationship

In both skeletal and cardiac muscle, the dihydropyridine (DHP) receptor is a critical element in excitation-contraction (e-c) coupling. However, the mechanism for calcium release is completely different in these muscles. In cardiac muscle the DHP receptor functions as a rapidly-activated calcium channel and the influx of calcium through this channel induces calcium release from the sarcoplasmic reticulum (SR). In contrast, in skeletal muscle the DHP receptor functions as a voltage sensor and as a slowly-activating calcium channel; in this case, the voltage sensor controls SR calcium release. It has been previously demonstrated that injection of dysgenic myotubes with cDNA (pCAC6) encoding the skeletal muscle DHP receptor restores the slow calcium current and skeletal type e-c coupling that does not require entry of external calcium (Tanabe, Beam, Powell, and Numa. 1988. Nature. 336:134-139). Furthermore, injection of cDNA (pCARD1) encoding the cardiac DHP receptor produces rapidly activating calcium current and cardiac type e-c coupling that does require calcium entry (Tanabe, Mikami, Numa, and Beam. 1990. Nature. 344:451-453). In this paper, we have studied the voltage dependence of, and the relationship between, charge movement, calcium transients, and calcium current in normal skeletal muscle cells in culture. In addition, we injected pCAC6 or pCARD1 into the nuclei of dysgenic myotubes and studied the relationship between the restored events and compared them with those of the normal cells. Charge movement and calcium currents were recorded with the whole cell patch-clamp technique. Calcium transients were measured with Fluo-3 introduced through the patch pipette. The kinetics and voltage dependence of the charge movement, calcium transients, and calcium current in dysgenic myotubes expressing pCAC6 were qualitatively similar to the ones elicited in normal myotubes: the calcium transient displayed a sigmoidal dependence on voltage and was still present after the addition of 0.5 mM Cd2+ + 0.1 mM La3+. In contrast, the calcium transient in dysgenic myotubes expressing pCARD1 followed the amplitude of the calcium current and thus showed a bell shaped dependence on voltage. In addition, the transient had a slower rate of rise than in pCAC6-injected myotubes and was abolished completely by the addition of Cd2+ + La3+.

Regulation of slow wave frequency by IP3-sensitive calcium release in the murine small intestine

2001 ◽  
Vol 280 (3) ◽  
pp. G439-G448 ◽  
Author(s):  
John Malysz ◽  
Graeme Donnelly ◽  
Jan D. Huizinga
Keyword(s):  
Small Intestine ◽  
Slow Wave ◽  
Calcium Release ◽  
Cyclopiazonic Acid ◽  
Slow Waves ◽  
Wave Frequency ◽  
Propagation Characteristics ◽  
Intracellular Ca ◽  
Stimulation Of

Slow waves determine frequency and propagation characteristics of contractions in the small intestine, yet little is known about mechanisms of slow wave regulation. We propose a role for intracellular Ca2+, inositol 1,4,5,-trisphosphate (IP3)-sensitive Ca2+ release, and sarcoplasmic reticulum (SR) Ca2+ content in the regulation of slow wave frequency because 1) 1,2-bis(2-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid-AM, a cytosolic Ca2+ chelator, reduced the frequency or abolished the slow waves; 2) thapsigargin and cyclopiazonic acid (CPA), inhibitors of SR Ca2+-ATPase, decreased slow wave frequency; 3) xestospongin C, a reversible, membrane-permeable blocker of IP3-induced Ca2+release, abolished slow wave activity; 4) caffeine and phospholipase C inhibitors (U-73122, neomycin, and 2-nitro-4-carboxyphenyl- N, N-diphenylcarbamate) inhibited slow wave frequency; 5) in the presence of CPA or thapsigargin, stimulation of IP3 synthesis with carbachol, norepinephrine, or phenylephrine acting on α1-adrenoceptors initially increased slow wave frequency but thereafter increased the rate of frequency decline, 6) thimerosal, a sensitizing agent of IP3 receptors increased slow wave frequency, and 7) ryanodine, a selective modulator of Ca2+-induced Ca2+ release, had no effect on slow wave frequency. In summary, these data are consistent with a role of IP3-sensitive Ca2+ release and the rate of SR Ca2+ refilling in regulation of intestinal slow wave frequency.

Differential modulation of caffeine- and IP3-induced calcium release in cultured arterial tissue

1999 ◽  
Vol 276 (5) ◽  
pp. C1115-C1120 ◽  
Author(s):  
Karl Dreja ◽  
Per Hellstrand
Keyword(s):  
Calcium Release ◽  
Cyclopiazonic Acid ◽  
Differential Modulation ◽  
Transient Responses ◽  
Inositol 1,4,5 Trisphosphate ◽  
Arterial Tissue ◽  
Intracellular Ca ◽  
Rat Tail

To investigate the Ca2+-dependent plasticity of sarcoplasmic reticulum (SR) function in vascular smooth muscle, transient responses to agents releasing intracellular Ca2+ by either ryanodine (caffeine) ord- myo-inositol 1,4,5-trisphosphate [IP3; produced in response to norepinephrine (NE), 5-hydroxytryptamine (5-HT), arginine vasopressin (AVP)] receptors in rat tail arterial rings were evaluated after 4 days of organ culture. Force transients induced by all agents were increased compared with those induced in fresh rings. Stimulation by 10% FCS during culture further potentiated the force and Ca2+ responses to caffeine (20 mM) but not to NE (10 μM), 5-HT (10 μM), or AVP (0.1 μM). The effect was persistent, and SR capacity was not altered after reversible depletion of stores with cyclopiazonic acid. The effects of serum could be mimicked by culture in depolarizing medium (30 mM K+) and blocked by the addition of verapamil (1 μM) or EGTA (1 mM) to the medium, lowering intracellular Ca2+ concentration ([Ca2+]i) during culture. These results show that modulation of SR function can occur in vitro by a mechanism dependent on long-term levels of basal [Ca2+]iand involving ryanodine- but not IP3 receptor-mediated Ca2+release.

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