Biomedical subjects

Jae Yeoul Jun

Publications and source records attributed to Jae Yeoul Jun.

At least 19 recordsLinked to original sources

PubMed2006

Effects of (-)-epigallocatechin-3-gallate on the activity of substantia nigra dopaminergic neurons.

Despite many studies on the biological and pharmacological properties of (-)-epigallocatechin-3-gallate (EGCG), an active component of green tea, information on neuronal modulation by EGCG is limited. This study was designed to investigate the effects of EGCG on the electrical activity of rat substantia nigra dopaminergic neurons using whole-cell patch clamp recordings. The spike frequency was increased to 6.33+/-0.23 (p<0.05) and 7.15+/-0.29 (p<0.05) by 5 and 10 microM EGCG, respectively, from the control level of 5.49+/-0.19 spikes/second, respectively (n=18). The resting membrane potential of the cells was decreased to -45.66+/-0.45 and -43.99+/-0.87 (p<0.05), by 5 and 10 microM EGCG, respectively, from -47.82+/-0.57 mV. The amplitude of afterhyperpolarization was decreased to 12.73+/-0.45 (p<0.05) and 11.60+/-0.57 (p<0.05) by 5 and 10 microM EGCG, respectively, from 13.80+/-0.31 mV. The neuronal activity of dopaminergic neurons is closely linked to dopamine release. When neurons switch from a single-spike firing to bursts of action potentials, the release of dopamine increases. The above experimental results suggest that EGCG increases the neuronal activity via inhibition of calcium-dependent potassium currents underlying the afterhyperpolarization, and it could act as a facilitating factor that elicits NMDA-dependent bursts of action potentials like apamin or bicuculline methiodide.

Animals↗

PubMed2006

Vasoactive intestinal polypeptide inhibits pacemaker activity via the nitric oxide-cGMP-protein kinase G pathway in the interstitial cells of Cajal of the murine small intestine.

Interstitial cells of Cajal (ICCs) are pacemaker cells that activate the periodic spontaneous depolarization (pacemaker potentials) responsible for the production of slow waves in gastrointestinal smooth muscle. The effects of vasoactive intestinal polypeptide (VIP) on the pacemaker potentials in cultured ICCs from murine small intestine were investigated by whole-cell patch-clamp techniques. Addition of VIP (50 nM-1 microM) decreased the amplitude of pacemaker potentials and depolarized resting membrane potentials. To examine the type of receptors involved in ICC, we examined the effects of the VIP1 agonist and found that it had no effect on pacemaker potentials. Pretreatment with VIP1 antagonist (1 microM) for 10 min also did not block the VIP (50 nM)-induced effects. On the other hand exposure to 1H-(1,2,4)oxadiazolo(4,3-A)quinoxalin- 1-one (ODQ, 100 microM), an inhibitor of guanylate cyclase, prevented VIP inhibition of pacemaker potentials. Similarly KT-5823 (1 microM) or RP-8-CPT-cGMPS (10 microM), inhibitors of protein kinase G (PKG) blocked the effect of VIP (50 nM) on pacemaker potentials as did N-nitro-L-arginine (L-NA, 100 mM), a non-selective nitric oxide synthase (NOS) inhibitor. These results imply that the inhibition of pacemaker activity by VIP depends on the NO-cGMP-PKG pathway.

Animals↗

PubMed2006

Bradykinin modulates pacemaker currents through bradykinin B2 receptors in cultured interstitial cells of Cajal from the murine small intestine.

We studied the modulation of pacemaker activities by bradykinin in cultured interstitial cells of Cajal (ICC) from murine small intestine with the whole-cell patch-clamp technique. Externally applied bradykinin produced membrane depolarization in the current-clamp mode and increased tonic inward pacemaker currents in the voltage-clamp mode. Pretreatment with bradykinin B1 antagonist did not block the bradykinin-induced effects on pacemaker currents. However, pretreatment with bradykinin B2 antagonist selectively blocked the bradykinin-induced effects. Also, only externally applied selective bradykinin B2 receptor agonist produced tonic inward pacemaker currents and ICC revealed a colocalization of the bradykinin B2 receptor and c-kit immunoreactivities, but bradykinin B1 receptors did not localize in ICC. External Na(+)-free solution abolished the generation of pacemaker currents and inhibited the bradykinin-induced tonic inward current. However, a Cl(-) channel blocker (DIDS) did not block the bradykinin-induced tonic inward current. The pretreatment with Ca(2+)-free solution and thapsigargin, a Ca(2+)-ATPase inhibitor in endoplasmic reticulum, abolished the generation of pacemaker currents and suppressed the bradykinin-induced action. Chelerythrine and calphostin C, protein kinase C inhibitors or naproxen, an inhibitor of cyclooxygenase, did not block the bradykinin-induced effects on pacemaker currents. These results suggest that bradykinin modulates the pacemaker activities through bradykinin B2 receptor activation in ICC by external Ca(2+) influx and internal Ca(2+) release via protein kinase C- or cyclooxygenase-independent mechanism. Therefore, the ICC are targets for bradykinin and their interaction can affect intestinal motility.

Animals↗

PubMed2006

Involvement of mitochondrial Na+-Ca2+ exchange in intestinal pacemaking activity.

AIM: Interstitial cells of Cajal (ICCs) are the pacemaker cells that generate slow waves in the gastrointestinal (GI) tract. We have aimed to investigate the involvement of mitochondrial Na+-Ca2+ exchange in intestinal pacemaking activity in cultured interstitial cells of Cajal. METHODS: Enzymatic digestions were used to dissociate ICCs from the small intestine of a mouse. The whole-cell patch-clamp configuration was used to record membrane currents (voltage clamp) and potentials (current clamp) from cultured ICCs. RESULTS: Clonazepam and CGP37157 inhibited the pacemaking activity of ICCs in a dose-dependent manner. Clonazepam from 20 to 60 micromol/L and CGP37157 from 10 to 30 micromol/L effectively inhibited Ca2+ efflux from mitochondria in pacemaking activity of ICCs. The IC50s of clonazepam and CGP37157 were 37.1 and 18.2 micromol/L, respectively. The addition of 20 micromol/L NiCl2 to the internal solution caused a "wax and wane" phenomenon of pacemaking activity of ICCs. CONCLUSION: These results suggest that mitochondrial Na+-Ca2+ exchange has an important role in intestinal pacemaking activity.

Animals↗

PubMed2006

Imipramine inhibits A-type delayed rectifier and ATP-sensitive K+ currents independent of G-protein and protein kinase C in murine proximal colonic myocytes.

The effects of imipramine on A-type delayed rectifier K+ currents and ATP-sensitive K+ (KATP) currents were studied in isolated murine proximal colonic myocytes using the whole-cell patch-clamp technique. Depolarizing test pulses between -80 mV and +30 mV with 10 mV increments from the holding potential of -80 mV activated voltage-dependent outward K+ currents that peaked within 50 ms followed by slow decreasing sustained currents. Early peak currents were inhibited by the application of 4-aminopyridine, whereas sustained currents were inhibited by the application of TEA. The peak amplitude of A-type delayed rectifier K+ currents was reduced by external application of imipramine. The half-inactivation potential and the half-recovery time of A-type delayed rectifier K+ currents were not changed by imipramine. With 0.1 mM ATP and 140 mM K+ in the pipette and 90 mM K+ in the bath solution and a holding potential of -80 mV, pinacidil activated inward currents; this effect was blocked by glibenclamide. Imipramine also inhibited KATP currents. The inhibitory effects of imipramine in A-type delayed rectifier K+ currents and KATP currents were not changed by guanosine 5-O-(2-thiodiphosphate) (GDPbetaS) and chelerythrine, a protein kinase C inhibitor. These results suggest that imipramine inhibits A-type delayed rectifier K+ currents and KATP currents in a manner independent of G-protein and protein kinase C.

4-Aminopyridine↗

PubMed2006

Activating of ATP-dependent K+ channels comprised of K(ir) 6.2 and SUR 2B by PGE2 through EP2 receptor in cultured interstitial cells of Cajal from murine small intestine.

The interstitial cells of Cajal (ICC) are pacemaker cells in gastrointestinal tract and generate an electrical rhythm in gastrointestinal muscles. We investigated the possibility that PGE(2) might affect the electrical properties of cultured ICC by activating ATP-dependent K(+) channels and, the EP receptor subtypes and the subunits of ATP-dependent K(+) channels involved in these activities were identified. In addition, the regulation of intracellular Ca(2+) ([Ca(2+)](i)) mobilization may be involved the action of PGE(2) on ICC. Treatments of ICC with PGE(2) inhibited electrical pacemaker activities in the same manner as pinacidil, an ATP-dependent K(+) channel opener and PGE(2) had only a dose-dependent effect. Using RT-PCR technique, we found that ATP-dependent K(+) channels exist in ICC and that these are composed of K(ir) 6.2 and SUR 2B subunits. To characterize the specific membrane EP receptor subtypes in ICC, EP receptor agonists and RT-PCR were used: Butaprost (an EP(2) receptor agonist) showed the actions on pacemaker currents in the same manner as PGE(2). However sulprostone (a mixed EP(1) and EP(3) agonist) had no effects. In addition, RT-PCR results indicated the presence of the EP(2) receptor in ICC. To investigate cAMP involvement in the effects of PGE(2) on ICCs, SQ-22536 (an inhibitor of adenylate cyclase) and cAMP assays were used. SQ-22536 did not affect the effect of PGE(2) on pacemaker currents, and PGE(2) did not stimulate cAMP production. Also, we found PGE(2) inhibited the spontaneous [Ca(2+)](i) oscillations in cultured ICC. These observations indicate that PGE(2) alters pacemaker currents by activating the ATP-dependent K(+) channels comprised of K(ir) 6.2-SUR 2B in ICC and this action of PGE(2) are through EP(2) receptor subtype and also the activation of ATP-dependent K(+) channels involves intracellular Ca(2+) mobilization.

ATP-Binding Cassette Transporters↗

PubMed2005

TRPC4 is an essential component of the nonselective cation channel activated by muscarinic stimulation in mouse visceral smooth muscle cells.

Classical transient receptor potential channels (TRPCs) are thought to be candidates for the nonselective cation channels (NSCCs) involved in pacemaker activity and its neuromodulation in murine stomach smooth muscle. We aimed to determine the role of TRPC4 in the formation of NSCCs and in the generation of slow waves. At a holding potential of -60 mV, 50 mM carbachol (CCh) induced INSCC of amplitude [500.8+/-161.8 pA (n=8)] at -60 mV in mouse gastric smooth muscle cells. We investigated the effects of commercially available antibodies to TRPC4 on recombinant TRPC4 expressed in HEK cells and CCh-induced NSCCs in gastric smooth muscle cells. TRPC4 currents in HEK cells were reduced from 1525.6+/-414.4 pA (n=8) to 146.4+/-83.3 pA (n=10) by anti-TRPC4 antibody and INSCC amplitudes were reduced from 230.9+/-36.3 pA (n=15) to 49.8+/-11.8 pA (n=9). Furthermore, INSCC in the gastric smooth muscle cells of TRPC4 knockout mice was only 34.4+/-10.4 pA (n=8) at -60 mV. However, slow waves were still present in the knockout mice. Our data suggest that TRPC4 is an essential component of the NSCC activated by muscarinic stimulation in the murine stomach.

Animals↗

PubMed2005

Action of imipramine on activated ATP-sensitive K(+) channels in interstitial cells of Cajal from murine small intestine.

Tricyclic antidepressants have been widely used for the treatment of depression and as a therapeutic agent for the altered gastrointestinal (GI) motility of irritable bowel syndrome (IBS). The aim of this study was to clarify whether antidepressants directly modulate pacemaker currents in cultured interstitial cells of Cajal (ICC). We used the whole-cell patch-clamp techniques at 30 degrees C in cultured ICC from the mouse small intestine. Treatment of pinacidil, an ATP-sensitive K(+) channel opener, in the ICC using the current clamping mode, produced hyperpolarization of the membrane potential and decreased the amplitude of the pacemaker potentials. With the voltage clamp mode, we observed a decrease in the frequency and amplitude of pacemaker currents and increases in the resting outward currents. These effects of pinacidil on pacemaker potentials and currents were completely suppressed by glibenclamide, an ATP-sensitive K(+) channel blocker. Also, with the current clamp mode, imipramine blocked the affect of pinacidil on the pacemaker potentials. Observations of the voltage clamp mode with imipramine, desipramine and amitryptyline suppressed the action of pinacidil in the ICC. Next, we examined whether protein kinase C (PKC) and the G protein are involved in the action of imipramine on pinacidil induced pacemaker current inhibition. We used chelerythrine, a potent PKC inhibitor and GDPbetaS, a nonhydrolyzable guanosine 5-diphosphate (GDP) analogue that permanently inactivates GTP-binding proteins. We found that pretreatment with chelerythrine and intracellular application of GDPbetaS had no influence on the blocking action of imipramine on inhibited pacemaker currents by pinacidil. We conclude that imipramine inhibited the activated ATP-sensitive K(+) channels in ICC. This action does not appear to be mediated through the G protein and protein kinase C. Furthermore, this study may suggest another possible mechanism for tricyclic antidepressants related modulation of GI motility.

ATP-Binding Cassette Transporters↗

PubMed2005

Effects of pine needle extract on pacemaker currents in interstitial cells of Cajal from the murine small intestine.

Extracts of pine needles (Pinus densiflora Sieb. et Zucc.) have diverse physiological and pharmacological actions. In this study we show that pine needle extract alters pacemaker currents in interstitial cells of Cajal (ICC) by modulating ATP-sensitive K+ channels and that this effect is mediated by prostaglandins. In whole cell patches at 30 degrees , ICC generated spontaneous pacemaker potentials in the current clamp mode (I = 0), and inward currents (pacemaker currents) in the voltage clamp mode at a holding potential of -70 mV. Pine needle extract hyperpolarized the membrane potential, and in voltage clamp mode decreased both the frequency and amplitude of the pacemaker currents, and increased the resting currents in the outward direction. It also inhibited the pacemaker currents in a dose-dependent manner. Because the effects of pine needle extract on pacemaker currents were the same as those of pinacidil (an ATP-sensitive K+ channel opener) we tested the effect of glibenclamide (an ATP-sensitive K+ channels blocker) on ICC exposed to pine needle extract. The effects of pine needle extract on pacemaker currents were blocked by glibenclamide. To see whether production of prostaglandins (PGs) is involved in the inhibitory effect of pine needle extract on pacemaker currents, we tested the effects of naproxen, a non-selective cyclooxygenase (COX-1 and COX-2) inhibitor, and AH6809, a prostaglandin EP1 and EP2 receptor antagonist. Naproxen and AH6809 blocked the inhibitory effects of pine needle extract on ICC. These results indicate that pine needle extract inhibits the pacemaker currents of ICC by activating ATP-sensitive K+ channels via the production of PGs.

Adenosine Triphosphate↗

PubMed2005

Deoxycholic acid inhibits pacemaker currents by activating ATP-dependent K+ channels through prostaglandin E2 in interstitial cells of Cajal from the murine small intestine.

1. We investigated the role of deoxycholic acid in pacemaker currents using whole-cell patch-clamp techniques at 30 degrees C in cultured interstitial cells of Cajal (ICC) from murine small intestine. 2. The treatment of ICC with deoxycholic acid resulted in a decrease in the frequency and amplitude of pacemaker currents and increases in resting outward currents. Also, under current clamping, deoxycholic acid produced the hyperpolarization of membrane potential and decreased the amplitude of the pacemaker potentials. 3. These observed effects of deoxycholic acid on pacemaker currents and pacemaker potentials were completely suppressed by glibenclamide, an ATP-sensitive K(+) channel blocker. 4. NS-398, a specific cyclooxygenase-2 (COX-2) inhibitor, significantly inhibited the deoxycholic acid-induced effects. The treatment with prostaglandin E(2) (PGE(2)) led to a decrease in the amplitude and frequency of pacemaker currents and to an increase in resting outward currents, and these observed effects of PGE(2) were blocked by glibenclamide. 5. We next examined the role of deoxycholic acid in the production of PGE(2) in ICC, and found that deoxycholic acid increased PGE(2) production through the induction of COX-2 enzyme activity and its gene expression. 6. The results suggest that deoxycholic acid inhibits the pacemaker currents of ICC by activating ATP-sensitive K(+) channels through the production of PGE(2).

Adenosine Triphosphate↗

PubMed2005

Melastatin-type transient receptor potential channel 7 is required for intestinal pacemaking activity.

BACKGROUND & AIMS: Interstitial cells of Cajal are pacemakers in the gastrointestinal tract, regulating rhythmicity by activating nonselective cation channels. In Caenorhabditis elegans, the melastatin-type transient receptor potential (TRPM) channel, especially TRPM7, was suggested as being involved in defecation rhythm. The aim here was to show that the nonselective cation channel in interstitial cells of Cajal in mouse small intestine has properties essentially identical to those of murine TRPM7, heterologously expressed in human embryonic kidney cells. METHODS: The patch-clamp technique for whole-cell recording was used in cultured or single interstitial cells of Cajal. TRPM7-specific small interfering RNAs were used for specific inhibition of TRPM7. RESULTS: Electrophysiological and pharmacological properties of the nonselective cation channel in interstitial cells of Cajal were the same as those of TRPM7. Reverse-transcription polymerase chain reaction, Western blotting, and immunohistochemistry all showed abundant and localized expression of TRPM7 messenger RNA and protein in mouse small intestine. Treatment of primary cultured interstitial cells of Cajal with TRPM7-specific small interfering RNA resulted in inhibition of pacemaking activity. CONCLUSIONS: TRPM7 is required for intestinal pacemaking. The protein is a likely potential target for pharmacological treatment of motor disorders of the gut.

Animals↗

PubMed2005

[Effects of tamoxifen on the voltage-dependent ionic currents in mouse colonic smooth muscle cells].

BACKGROUND/AIMS: Tamoxifen is a widely used anticancer drug for breast cancer with frequent gastrointestinal side effects. Changes in gastrointestinal motility is associated with altered activities of membrane ion channels. Ion channels have important role in regulating membrane potential and cell excitability. This study was performed to investigate the effects of tamoxifen on the membrane ionic currents in colonic smooth muscle cells. METHODS: Murine colonic smooth muscle cells were isolated from the proximal colon using collagenase, and the membrane currents were recorded using a whole-cell patch clamp technique. RESULTS: Two types of voltage-dependent K(+) currents were recorded (A-type and delayed rectifier K(+) currents). Tamoxifen inhibited both types of voltage-dependent K(+) currents in a dose-dependent manner. However, tamoxifen did not change the half-inactivation potential and the recovery time of voltage-dependent K(+) currents. Chelerythrine, a protein kinase C inhibitor or phorbol 12, 13-dibutyrate, a protein kinase C activator did not affect the voltage-dependent K(+) currents. Guanosine 5'-O-(2-thio-diphosphate) did not affect the tamoxifen-induced inhibition of voltage-dependent K(+) currents. Tamoxifen inhibited voltage-dependent Ca(2+) currents completely in whole-test ranges. CONCLUSIONS: These results suggest that tamoxifen can alter various membrane ionic currents in smooth muscle cells and cause some adverse effects on the gastrointestinal motility.

Animals↗

PubMed2004

Substance P induces inward current and regulates pacemaker currents through tachykinin NK1 receptor in cultured interstitial cells of Cajal of murine small intestine.

We investigated whether substance P modulates pacemaker currents generated in cultured interstitial cells of Cajal of murine small intestine using whole cell patch-clamp techniques at 30 degrees C. Interstitial cells of Cajal generated spontaneous inward currents (pacemaker currents) at a holding potential of -70 mV. Tetrodotoxin, nifedipine, tetraethylammonium, 4-aminopyridine, or glibenclamide did not change the frequency and amplitude of pacemaker currents. However, divalent cations (Ni2+, Mn2+, Cd2+, and Co2+), nonselective cationic channel blockers (gadolinium and flufenamic acid), and a reduction of external Na+ from normal to 1 mM inhibited pacemaker currents indicating that nonselective cation channels are involved in their generation. Substance P depolarized the membrane potential in current clamp mode and produced tonic inward pacemaker currents with reduced frequency and amplitude in voltage clamp mode. [D-Arg1, D-Trp7,9, Leu11] substance P, a tachykinin NK1 receptor antagonist, blocked these substance P-induced responses. Furthermore, [Sar9, Met(O2)11] substance P, a specific tachykinin NK1 receptor agonist, depolarized the membrane and tonic inward currents mimicked those of substance P. Substance P continued to produce tonic inward currents in external Ca2+-free solution or in the presence of chelerythrine, a protein kinase C inhibitor. However, substance P-induced tonic inward currents were blocked by thapsigargin, a Ca2+-ATPase inhibitor in the endoplasmic reticulum or by an external 1 mM Na+ solution. Our results demonstrate that substance P may modulate intestinal motility by acting on the interstitial cells of Cajal by activating nonselective cation channels via the release of intracellular Ca2+ induced by tachykinin NK1 receptor stimulation.

4-Aminopyridine↗

PubMed2004

Noradrenaline inhibits pacemaker currents through stimulation of beta 1-adrenoceptors in cultured interstitial cells of Cajal from murine small intestine.

1. Interstitial cells of Cajal (ICCs) are pacemaker cells that activate the periodic spontaneous inward currents (pacemaker currents) responsible for the production of slow waves in gastrointestinal smooth muscle. The effects of noradrenaline on the pacemaker currents in cultured ICCs from murine small intestine were investigated by using whole-cell patch-clamp techniques at 30 degrees C. 2. Under current clamping, ICCs had a mean resting membrane potential of -58+/-5 mV and produced electrical slow waves. Under voltage clamping, ICCs produced pacemaker currents with a mean amplitude of -410+/-57 pA and a mean frequency of 16+/-2 cycles min(-1). 3. Under voltage clamping, noradrenaline inhibited the amplitude and frequency of pacemaker currents and increased resting currents in the outward direction in a dose-dependent manner. These effects were reduced by intracellular GDP beta S. 4. Noradrenaline-induced effects were blocked by propranolol (beta-adrenoceptor antagonist). However, neither prazosin (alpha(1)-adrenoceptor antagonist) nor yohimbine (alpha(2)-adrenoceptor antagonist) blocked the noradrenaline-induced effects. Phenylephrine (alpha(1)-adrenoceptor agonist) had no effect on the pacemaker currents, whereas isoprenaline (beta-adrenoceptor agonist) mimicked the effect of noradrenaline. Atenolol (beta(1)-adrenoceptor antagonist) blocked the noradrenaline-induced effects, but butoxamine (beta(2)-adrenoceptor antagonist) did not. In addition, BRL37344 (beta(3)-adrenoceptor agonist) had no effect on pacemaker currents. 5. 9-(Tetrahydro-2-furanyl)-9H-purine-6-amine (SQ-22536; adenylate cyclase inhibitor) and a myristoylated protein kinase A inhibitor did not inhibit the noradrenaline-induced effects and 8-bromo-cAMP had no effects on pacemaker currents. 8-Bromo-cGMP and SNAP inhibited pacemaker currents and these effects of SNAP were blocked by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; a guanylate cyclase inhibitor). However, ODQ did not block the noradrenaline-induced effects. 6. Neither tetraethylammonium (a voltage-dependent K(+) channel blocker), apamin (a Ca(2+)-dependent K(+) channel blocker) nor glibenclamide (an ATP-sensitive K(+) channel blocker) blocked the noradrenaline-induced effects. 7. The results suggest that noradrenaline-induced stimulation of beta(1)-adrenoceptors in the ICCs inhibits pacemaker currents, and that this is mediated by the activation of G-protein. Neither adenylate cyclase, guanylate cyclase nor a K(+) channel-dependent pathway are involved in this effect of noradrenaline.

Adenylyl Cyclase Inhibitors↗

PubMed2003

Excitatory effects of 5-hydroxytryptamine on the medial vestibular nuclear neuron via the 5-HT2 receptor.

This study was designed to investigate the mechanisms of action of the 5-HT2 receptor on the spontaneous electrical activity and potassium currents of the rat medial vestibular nuclear neurons using whole-cell patch clamp recordings. The spike width of spontaneous action potential was not affected by 5-alpha-methylhydroxytryptamine. The spike frequency and resting membrane potential was increased by 5-alpha-methylhydroxytryptamine. The amplitude of afterhyperpolarization was decreased by 5-alpha-methylhydroxy-tryptamine. The peak current of the potassium currents of the neuron treated with 5-alpha-methylhydroxytryptamine was decreased. After blockade of calcium-dependent potassium currents, 5-alpha-methylhydroxytryptamine did not inhibit potassium currents. These results suggest 5-alpha-methylhydroxytryptamine increases spontaneous firing of the medial vestibular nuclear neurons by inhibiting calcium dependent potassium currents.

Action Potentials↗

PubMed2003

[Characterization of pacemaking currents in cultured interstitial cells of Cajal from mice small intestine].

BACKGROUND/AIMS: Gastrointestinal motility is initiated by the periodic generation of slow waves. Interstitial cells of Cajal (ICC) are pacemaker cells that generate slow waves and drive spontaneous mechanical contractions of the gastrointestinal smooth muscle. Slow waves generate the periodic activation of spontaneous inward currents (pacemaker currents). The aim of this study was to investigate the characterization of pacemaker currents of ICC. METHODS: The ICC in mice small intestine were cultured with stem cell factor for 2 days, and then we recorded pacemaker currents and slow waves using a whole-cell patch clamp technique. RESULTS: Under voltage clamp at -80 mV of holding potential, ICC generated pacemaker currents. Tetrodotoxin and nifedipine did not affect on the pacemaker currents. In addition, tetraethylammonium, 4-aminopyridine and glibenclamide did not affect on the pacemaker currents. The reduction of external Na+ concentrations inhibited pacemaker currents. Moreover, these currents were completely abolished in the external Ca2+-free condition. Gadolinium and flufenamic acid, inhibitors of non-selective cationic currents, inhibited pacemaker currents. Thapsigargin and cyclopiazoic acid, inhibitors of Ca2+-ATPase in endoplasmic reticulum, abolished pacemaker currents. Carbachol depolarized membrane potential and increased inward currents. CONCLUSIONS: These results suggest that pacemaker currents are mediated by the activation of non-selective cation channel and become a target of neurotransmitters in regulation of intestinal motility.

Animals↗

PubMed2002

A Ca(2+)-inhibited non-selective cation conductance contributes to pacemaker currents in mouse interstitial cell of Cajal.

Interstitial cells of Cajal (ICC) provide pacemaker activity in some smooth muscles. The nature of the pacemaker conductance is unclear, but studies suggest that pacemaker activity is due to a voltage-independent, Ca(2+)-regulated, non-selective cation conductance. We investigated Ca(2+)-regulated conductances in murine intestinal ICC and found that reducing cytoplasmic Ca(2+) activates whole-cell inward currents and single-channel currents. Both the whole-cell currents and single-channel currents reversed at 0 mV when the equilibrium potentials of all ions present were far from 0 mV. Recordings from on-cell patches revealed oscillations in unitary currents at the frequency of pacemaker currents in ICC. Voltage-clamping cells to -60 mV did not change the oscillatory activity of channels in on-cell patches. Depolarizing cells with high external K(+) caused loss of resolvable single-channel currents, but the oscillatory single-channel currents were restored when the patches were stepped to negative potentials. Unitary currents were also resolved in excised patches. The single-channel conductance was 13 pS, and currents reversed at 0 mV. The channels responsible were strongly activated by 10(-7) M Ca(2+), and 10(-6) M Ca(2+) reduced activity. The 13 pS channels were strongly activated by the calmodulin inhibitors calmidazolium and W-7 in on-cell and excised patches. Calmidazolium and W-7 also activated a persistent inward current under whole-cell conditions. Murine ICC express Ca(2+)-inhibited, non-selective cation channels that are periodically activated at the same frequency as pacemaker currents. This conductance may contribute to the pacemaker current and generation of electrical slow waves in GI muscles.

Analgesics↗

PubMed2002

Postnatal development of parvalbumin and calbindin D-28k immunoreactivities in the canine anterior cingulate cortex: transient expression in layer V pyramidal cells.

We have examined the ontogeny of parvalbumin (PV) and calbindin D-28k (CB) immunoreactivities in the canine anterior cingulate cortex (ACC) from the day of birth (P0) through P180. At P7, PV immunoreactivity first appeared in layer VI multipolar cells. The PV immunoreactivity in GABAergic nonpyramidal cells appeared to follow an inside-out gradient of radial emergence. Although immunoreaction was limited mainly to the developing nonpyramidal cells, pyramid-like PV immunoreactive cells were transitorily observed in layer V from P14 to P90. The developmental pattern of CB immunoreactivity differed from that of PV immunoreactivity. CB immunoreactivity first developed in layer V pyramidal cells from P0, which continued through P90. CB immunoreactive nonpyramidal cells were located in the infragranular layers and white matter at P0 and matured in both the supragranular and infragranular layers without clear inside-out gradient. This developmental study revealed the comparable belated expression of PV immunoreactivity and the transient expression of both calcium-binding proteins in layer V pyramidal cells. These results suggest that the transient expression of calcium-binding proteins in layer V pyramidal cells might be related to the critical period of early postnatal development.

Aging↗