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H Yawo

Publications and source records attributed to H Yawo.

At least 19 recordsLinked to original sources
PubMed2005

Synapse-to-synapse variation of calcium channel subtype contributions in large mossy fiber terminals of mouse hippocampus.

Both N- and P/Q-type voltage-dependent calcium channels are involved in fast transmitter release in the hippocampus, but are differentially regulated. Although variable contributions of voltage-dependent calcium channel subtypes to presynaptic Ca2+ influx have been suggested to give a neural network of great diversity, their presence has only been demonstrated in a culture system and has remained unclear in the brain. Here, the individual large mossy fiber presynaptic terminal was labeled with Ca2+/Sr2+-sensitive fluorescent dextrans in the hippocampal slice of the mouse. The fractional contribution of voltage-dependent calcium channel subtypes to presynaptic Ca2+/Sr2+ influx was directly measured by the sensitivity of Ca2+/Sr2+-dependent fluorescent increment to subtype-selective neurotoxins, omega-conotoxin GVIA (an N-type selective blocker), omega-agatoxin IVA (a P/Q-type selective blocker) and SNX-482 (an R-type selective blocker). Synapse-to-synapse comparison of large mossy fiber terminals revealed that the contributions of N- and R-type voltage-dependent calcium channels varied more widely than that of P/Q-type. Even two large mossy fiber presynaptic terminals neighboring on the same axon differed in the fractional contributions of N- and R-type voltage-dependent calcium channels. On the other hand, these terminals were similar in the fractional contributions of P/Q-type voltage-dependent calcium channels. These results provide direct evidence that individual large mossy fiber synapses are differential in the contribution of N- and R-type voltage-dependent calcium channel subtypes to presynaptic Ca2+/Sr2+ influx. We suggest that the synapse-to-synapse variation of presynaptic voltage-dependent calcium channel subtype contributions may be one of the mechanisms amplifying diversity of the hippocampal network.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed2000

Re-evaluation of phorbol ester-induced potentiation of transmitter release from mossy fibre terminals of the mouse hippocampus.

To investigate the mechanisms by which phorbol esters potentiate transmitter release from mossy fibre terminals we used fura dextran to measure the intraterminal Ca2+ concentration in mouse hippocampal slices. A phorbol ester, phorbol 12,13-diacetate (PDAc), potentiated the field excitatory postsynaptic potential (fEPSP) slope. PDAc also enhanced the stimulation-dependent increase of [Ca2+]i in the mossy fibre terminal (Delta[Ca2+]pre). The magnitude of the PDAc-induced fEPSP potentiation (463+/-57% at 10 microM) was larger than that expected from the enhancement of Delta[Ca2+]pre (153+/-5%). The Delta[Ca2+]pre was suppressed by omega-agatoxin IVA (omega-AgTxIVA, 200 nM), a P/Q-type Ca2+ channel-specific blocker, by 31%. The effect of PDAc did not select between omega-AgTxIVA-sensitive and -resistant components. The PDAc-induced potentiation of the fEPSP slope was partially antagonized by the protein kinase C (PKC) inhibitor bisindolylmaleimide I (BIS-I, 10 microM), whereas the Delta[Ca2+]pre was completely blocked by BIS-I. Although the BIS-I-sensitive fEPSP potentiation was accompanied by a reduction of the paired-pulse ratio (PPR), the BIS-I-resistant component was not. Whole-cell patch clamp recording from a CA3 pyramidal neuron in a BIS-I-treated slice demonstrated that PDAc (10 microM) increased the frequency of miniature excitatory postsynaptic currents (mEPSCs, 259+/-33% of control) without a noticeable change in their amplitude (102+/-5% of control). These results suggest that PKC potentiates transmitter release by at least two distinct mechanisms, one Delta[Ca2+]pre dependent and the other Delta[Ca2+]pre independent. In addition, some phorbol ester-mediated potentiation of synaptic transmission appears to occur without activating PKC.

Action Potentials↗
PubMed2000

mu-Opioid receptor inhibits N-type Ca2+ channels in the calyx presynaptic terminal of the embryonic chick ciliary ganglion.

A study was made on the mechanisms by which enkephalins inhibit synaptic transmission at calyx-type presynaptic terminals in the ciliary ganglion of chick embryos at stages 39-40. Excitatory postsynaptic currents (EPSCs) were recorded by nystatin-perforated patch clamp at low [Ca2+]o and high [Mg2+]o. [Leu5]enkephalin (L-ENK, 1-10 microM) reduced the quantal content (m) without changing the quantal size (q). This effect was antagonized by naloxone (1 microM). Similar results were observed under conventional whole-cell clamp of the postsynaptic neuron. A specific agonist of the mu-opioid receptor, [D-Ala2, M-Me-Phe4,Gly5]enkephalin-ol (DAMGO) reduced m without changing q. A specific agonist of the delta-opioid receptor, [d-Pen2, d-Pen5]enkephalin (DPDPE) also reduced m without changing q. Both L-ENK and [Met5]enkephalin (M-ENK) reduced the stimulus-dependent increment of the intraterminal Ca2+ concentration (Delta[Ca2+]t) without affecting the decay time constant of the intraterminal Ca2+ concentration and basal Ca2+ level. This effect was antagonized by naloxone. DAMGO reduced Delta[Ca2+]t more effectively than DPDPE. When extracellular Ca2+ was replaced by Ba2+, the stimulus-dependent increment of the intraterminal Ba2+ concentration (Delta[Ba2+]t) was also reduced by L-ENK or DAMGO. L-ENK reduced Delta[Ca2+]t even in the presence of 4-aminopyridine (4-AP), which blocks the transient K+ conductance during the falling phase of the presynaptic action potential. When N-type Ca2+ channels were blocked by omega-conotoxin GVIA (omega-CgTxGVIA), the Delta[Ca2+]t was no longer sensitive to L-ENK and DAMGO. It is suggested that enkephalins reduce the transmitter release through presynaptic opioid receptors. The mu-opioid receptor may suppress presynaptic Ca2+ influx by selectively inhibiting N-type Ca2+ channels.

Analgesics, Opioid↗
PubMed1999

Involvement of cGMP-dependent protein kinase in adrenergic potentiation of transmitter release from the calyx-type presynaptic terminal.

I have previously reported that norepinephrine (NE) induces a sustained potentiation of transmitter release in the chick ciliary ganglion through a mechanism pharmacologically distinct from any known adrenergic receptors. Here I report that the adrenergic potentiation of transmitter release was enhanced by a phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX) and by zaprinast, an inhibitor of cGMP-selective phosphodiesterase. Exogenous application of the membrane-permeable cGMP, 8-bromo-cGMP (8Br-cGMP), potentiated the quantal transmitter release, and after potentiation, the addition of NE was no longer effective. On the other hand, 8Br-cAMP neither potentiated the transmitter release nor occluded the NE-induced potentiation. The NE-induced potentiation was blocked by neither nitric oxide (NO) synthase inhibitor nor NO scavenger. The quantal transmitter release was not potentiated by NO donors, e.g., sodium nitroprusside. The NE-induced potentiation and its enhancement by IBMX was antagonized by two inhibitors of protein kinase G (PKG), Rp isomer of 8-(4-chlorophenylthio) guanosine-3', 5'-cyclic monophosphorothioate and KT5823. As with NE-induced potentiation, the effects of 8Br-cGMP on both the resting intraterminal [Ca2+] ([Ca2+]i) and the action potential-dependent increment of [Ca2+]i (DeltaCa) in the presynaptic terminal were negligible. The reduction of the paired pulse ratio of EPSC is consistent with the notion that the NE- and cGMP-dependent potentiation of transmitter release was attributable mainly to an increase of the exocytotic fusion probability. These results indicate that NE binds to a novel adrenergic receptor that activates guanylyl cyclase and that accumulation of cGMP activates PKG, which may phosphorylate a target protein involved in the exocytosis of synaptic vesicles.

Adrenergic Antagonists↗
PubMed1999

Identification of a novel gene family encoding human liver-specific organic anion transporter LST-1.

We have isolated a novel liver-specific organic anion transporter, LST-1, that is expressed exclusively in the human, rat, and mouse liver. LST-1 is a new gene family located between the organic anion transporter family and prostaglandin transporter. LST-1 transports taurocholate (Km = 13.6 microM) in a sodium-independent manner. LST-1 also shows broad substrate specificity. It transports conjugated steroids (dehydroepiandrosterone sulfate, estradiol-17beta-glucuronide, and estrone-3-sulfate), eicosanoids (prostaglandin E2, thromboxane B2, leukotriene C4, leukotriene E4), and thyroid hormones (thyroxine, Km = 3.0 microM and triiodothyronine, Km = 2.7 microM), reflecting hepatic multispecificity. LST-1 is probably the most important transporter in human liver for clearance of bile acids and organic anions because hepatic levels of another organic anion transporter, OATP, is very low. This is also the first report of the human molecule that transports thyroid hormones.

Amino Acid Sequence↗
PubMed1999

Two components of transmitter release from the chick ciliary presynaptic terminal and their regulation by protein kinase C.

1. A study was made of the effects of phorbol ester (phorbol 12-myristate 13-acetate, PMA, 0.1 microM) on the two components of evoked transmitter release, namely the fast synchronous and the slow asynchronous components, from the giant presynaptic terminal of the chick ciliary ganglion. The excitatory postsynaptic currents (EPSCs) were recorded under whole-cell voltage clamp of the postsynaptic neuron. 2. The decay time constant of the slow component was prolonged by replacing Ca2+ with Sr2+. In 5 mM [Sr2+]o the fast component decayed with a time constant of 2.6 +/- 1.4 ms whereas the slow component decayed with a time constant of 19 +/- 7 ms. 3. When stimulated with twin pulses with a short interpulse interval, the fast component of the second EPSC was often depressed whereas the slow component was usually facilitated. Both components were positively dependent on [Sr2+]o in a saturable manner, but the fast component approached its maximum at a lower [Sr2+]o than the slow component. 4. PMA potentiated both the fast and slow components to a similar extent and with a similar time course. For each component, the effect of PMA was less potent at high [Sr2+]o than at low [Sr2+]o. For either the fast or the slow component the PMA-induced potentiation was accompanied by a reduction in the paired-pulse ratio (PPR). 5. Despite the different dissociation constant for dextran-conjugated fura-2, the fluorescent ratio for intraterminal [Sr2+] ([Sr2+]i) decayed to the baseline after the nerve-evoked increment with a time course similar to that for [Ca2+]i, suggesting that intraterminal Sr2+ is buffered less efficiently than Ca2+. PMA did not increase the [Sr2+]i transients produced by stimulation of the presynaptic oculomotor nerve. 6. It is suggested that protein kinase C (PKC) modulates both the fast and slow components through common molecular mechanisms that upregulate the Sr2+ sensitivity of the vesicle fusion probability.

Algorithms↗
PubMed1999

Immunohistochemical distribution and functional characterization of an organic anion transporting polypeptide 2 (oatp2).

The rabbit polyclonal antibody against rat organic anion transporting polypeptide 2 (oatp2) was raised and immunoaffinity-purified. Western blot analysis for oatp2 detected two bands ( 74 and 76 kDa) in rat brain and a single band (76 kDa) in the liver. By immunohistochemical analysis, the oatp2 immunoreactivity was specifically high at the basolateral membrane of rat hepatocytes. Functionally, the oatp2-expressing oocytes were found to transport dehydroepiandrosterone sulfate, delta1 opioid receptor agonist [D-Pen2,D-Pen5]enkephalin, Leuenkephalin, and biotin significantly, as well as the substrates previously reported. These data reveal the exact distribution of the rat oatp2 at the protein level in the liver, and that oatp2 appears to be involved in the multispecificity of the uptaking substrates in the liver and brain.

Animals↗
PubMed1999

Protein kinase C potentiates transmitter release from the chick ciliary presynaptic terminal by increasing the exocytotic fusion probability.

1. The giant presynaptic terminal of chick ciliary ganglion was used to examine how protein kinase C (PKC) modulates neurotransmitter release. Cholinergic excitatory postsynaptic currents (EPSCs) were recorded under whole-cell voltage clamp. 2. Although the EPSC was potentiated by phorbol ester (phorbol 12-myristate 13-acetate, PMA; 0.1 microM) in a sustained manner, the nicotine-induced current was unaffected. PMA increased the quantal content to 2.4 +/- 0.4 (n = 9) of control without changing the quantal size. 3. The inactive isoform of PMA, 4alpha-PMA, showed no significant effect on EPSCs. The PMA-induced potentiation was antagonized by two PKC inhibitors with different modes of action, sphingosine (20 microM) and bisindolylmaleimide I (10 microM). 4. When stimulated by twin pulses of short interval, the second EPSC was on average larger than the first EPSC (paired-pulse facilitation; PPF). PMA significantly decreased the PPF ratio with a time course similar to that of the potentiation of the first EPSC. 5. PMA did not affect resting [Ca2+]i or the action potential-induced [Ca2+]i increment in the giant presynaptic terminals. 6. The effect of PMA was less at 10 mM [Ca2+]o than at 1 mM [Ca2+]o. 7. When a train of action potentials was generated with a short interval, the EPSC was eventually depressed and reached a steady-state level. The recovery process followed a simple exponential relation with a rate constant of 0.132 +/- 0.029 s-1. PMA did not affect the recovery rate constant of EPSCs from tetanic depression. In addition, PMA did not affect the steady-state EPSC which should be proportional to the refilling rate of the readily releasable pool of vesicles. 8. These results conflict with the hypothesis that PKC upregulates the size of the readily releasable pool or the number of release sites. PKC appears to upregulate the Ca2+ sensitivity of the process that controls the exocytotic fusion probability.

Action Potentials↗
PubMed1999

Molecular characterization and functional regulation of a novel rat liver-specific organic anion transporter rlst-1.

BACKGROUND & AIMS: Recently, we isolated a new complementary DNA (cDNA) encoding human liver-specific organic anion transporter (LST-1), representing the multispecificity of human liver. The aim of this study was to isolate a rat counterpart of human LST-1 and examine the expression regulation of its messenger RNA (mRNA) to clarify the molecular basis of cholestasis. METHODS: A rat liver cDNA library was screened with human LST-1 cDNA as a probe. Xenopus oocyte expression system was used for functional analysis. Northern blot analyses were performed using the isolated cDNA (termed rlst-1). The bile duct ligation model and the cecum ligation and puncture model were used for expression analyses. RESULTS: rlst-1 encodes 652 amino acids, predicting at least 11 transmembrane regions. The overall homology with human LST-1 was 60.2%, which is the highest among all known organic anion transporters. rlst-1 also belongs to the same new gene family as human LST-1, located between the organic anion transporter family and the prostaglandin transporter. rlst-1 preferably transports taurocholate (K(m), 9.45 micromol/L) in an Na(+)-independent manner. The rlst-1 mRNA is exclusively expressed in the liver. In both the bile duct ligation model and the cecum ligation and puncture model, mRNA expression levels of rlst-1 were down-regulated. CONCLUSIONS: rlst-1 is a counterpart of human LST-1 and is one of the important transporters in rat liver for the clearance of bile acid. The expression of rlst-1 may be under feedback regulation of cholestasis by biliary obstruction and/or sepsis.

Amino Acid Sequence↗
PubMed1999

Pravastatin, an HMG-CoA reductase inhibitor, is transported by rat organic anion transporting polypeptide, oatp2.

PURPOSE: We previously demonstrated the HMG-CoA reductase inhibitor, pravastatin, is actively taken up into isolated rat hepatocytes through multispecific organic anion transporters. The present study examined whether a newly cloned organic anion transporting polypeptide (oatp2) transports pravastatin. METHODS: We investigated functional expression of oatp2 in Xenopus laevis oocytes, to examine [14C] pravastatin uptake. RESULTS: [14C] Pravastatin (30 microM) uptake into oatp2 cRNA-injected oocytes was 40 times higher than that of water-injected control oocytes. The oatp2-mediated pravastatin uptake was Na+-independent and saturable. The Michaelis-Menten constant was 37.5+/-9.9 microM, a level comparable to that obtained in isolated rat hepatocytes in our previous study. As is the case with rat hepatocytes, the uptake of pravastatin (30 microM) was inhibited by 300 microM concentrations of taurocholate, cholate, bromosulfophthalein, estradiol-17beta-glucuronide, and simvastatin acid, but not by para-aminohippurate. On the other hand, [14C] simvastatin acid (30 microM) uptake of oatp2 cRNA-injected oocytes was not significantly different from that of water-injected oocytes. CONCLUSIONS: The cloned oatp2 was identified as the transporter responsible for the active hepatocellular pravastatin uptake.

Animals↗
PubMed1998

Molecular characterization and tissue distribution of a new organic anion transporter subtype (oatp3) that transports thyroid hormones and taurocholate and comparison with oatp2.

Two complementary DNAs for the organic anion transporter subtypes oatp2 and oatp3, which transport thyroid hormones as well as taurocholate, were isolated from a rat retina cDNA library. The sequence of oatp2 is identical to that recently reported (Noé, B., Hagenbuch, B., Stieger, B., and Meier, P. J. (1997) Proc. Natl. Acad. Sci. U. S. A. 94, 10346-10350), whereas the sequence of oatp3 is novel. oatp3 consists of 670 amino acid residues and exhibits a structural architecture common to the organic anion transporter family, possessing the 12 putative membrane-spanning segments. Oocytes injected with oatp2 and oatp3 cRNAs showed taurocholate uptake in a saturable manner. The oatp2 and oatp3 cRNA-injected oocytes also showed significant uptake of both thyroxine and triiodothyronine. Northern blot and in situ analyses showed that the oatp2 mRNA was widely expressed in neuronal cells of the central nervous system, especially in the hippocampus, cerebellum, and choroid plexus as well as in the retina and liver. The oatp3 mRNA was highly expressed in the kidney and moderately abundant in the retina. This suggests that oatp2 and oatp3 are multifunctional transporters involved in the transport of thyroid hormones in the brain, retina, liver, and kidney.

Amino Acid Sequence↗
PubMed1996

Noradrenaline modulates transmitter release by enhancing the Ca2+ sensitivity of exocytosis in the chick ciliary presynaptic terminal.

1. The giant presynaptic terminal of chick ciliary ganglion was used to examine how noradrenaline (NA) modulates neurotransmitter release. The cholinergic excitatory postsynaptic currents (EPSCs) were recorded under whole-cell voltage clamp of the postsynaptic neuron. 2. Although the EPSC was potentiated by NA, the current directly activated by acetylcholine (IACh) was unaffected. NA also increased the quantal contents without changing the quantal size. 3. The NA-dependent potentiation was antagonized by neither phentolamine nor propranolol. The EPSC was also potentiated by adrenaline and dopamine but not by normetanephrine, phenylephrine or isoprenaline. The EPSC was attenuated by clonidine. Therefore, NA potentiated the transmitter release through a receptor pharmacologically different from both alpha- and beta-adrenergic receptors. 4. The Ca2+ increment produced by an action potential (delta[Ca2+]pre) was reduced by NA through an alpha 2-adrenergic receptor. However, when alpha 2-adrenergic receptors were blocked, neither delta[Ca2+]pre nor resting Ca2+ were changed by NA. 5. The [Ca2+]o-EPSC relation was shifted by NA, decreasing the half-saturating [Ca2+]o, without changing the maximum. 6. It is concluded that NA-dependent potentiation of transmitter release was due to an increase in the Ca2+ sensitivity of the exocytotic process. The enhancement of the fusion probability is suggested.

Action Potentials↗
PubMed1994

Omega-conotoxin-sensitive and -resistant transmitter release from the chick ciliary presynaptic terminal.

1. Synaptically evoked responses to stimulation of the oculomotor nerve were recorded from the ciliary nerve in chick embryos. The postsynaptic currents in response to presynaptic stimulation (EPSCs) were also recorded under whole-cell voltage clamp of the ciliary cell. 2. The ciliary nerve response was dependent on the extracellular Ca2+ concentration ([Ca2+]o). omega-Conotoxin GVIA (omega-CgTX, 100 nM) increased the [Ca2+]o necessary to evoke the half-maximal response by a factor of 1.7 without changing the slope of [Ca2+]o dependence. Dihydropyridine (DHP) derivatives, nifedipine or Bay K 8644, did not affect the [Ca2+]o sensitivity of ciliary nerve response. 3. The EPSC was usually preceded by the capacitive coupling response of the presynaptic action potential. In some records, the EPSCs were also preceded by the electrical coupling responses which were the mirror images of the presynaptic action potentials. The current-voltage relation of the EPSCs showed inward rectification. 4. The EPSC was potentiated by 4-aminopyridine (4-AP) as a result of prolongation of the falling phase of presynaptic action potential. In the presence of high [Ca2+]o and 4-AP, a small fraction of EPSC was resistant to omega-CgTX. 5. The resting potential of the presynaptic terminal was changed from -69 to -57 mV by increasing [K+]o from 1 to 10 mM. The same procedure decreased the omega-CgTX-resistant EPSC by 30%, whereas the omega-CgTX-untreated EPSC in low-Ca2+ saline was not affected by the change in [K+]o. 6. The nerve-evoked increase in intracellular Ca2+ was recorded from the presynaptic terminal (delta[Ca2+]pre). The delta[Ca2+]pre was larger in a solution containing 10 mM Ca2+ and 1 mM K+ after treating with omega-CgTX than in a solution containing 2 mM Ca2+ and 16 mM Mg2+ before treating with omega-CgTX. The EPSC was, in contrast, smaller in the 10 mM Ca(2+)-1 mM K+ solution after omega-CgTX treatment than in the 2 mM Ca(2+)-16 mM Mg2+ solution before omega-CgTX treatment. 7. Similarly, the EPSC was smaller in the 10 mM Ca(2+)-1 mM K+ solution containing 5 microM La3+ than in the 2 mM Ca(2+)-16 mM Mg2+ solution, whereas the delta [Ca2+]pre was larger in the 10 mM Ca(2+)-1 mM K+ solution containing 5 micrograms La3+ than in the 2 mM Ca(2+)-16 mM Mg2+ solution. 8. It is concluded that the omega-CgTX-sensitive Ca2+ conductance of the presynaptic terminal is the principal source of Ca2+ involved in transmitter release.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Preferential inhibition of omega-conotoxin-sensitive presynaptic Ca2+ channels by adenosine autoreceptors.

Adenosine is a potent modulator of transmitter release at a variety of synapses. The adenosine A1 receptor is assumed to reside in presynaptic terminals and to function as a negative autoreceptor. How adenosine reduces transmitter release is uncertain; it may reduce the calcium influx during nerve terminal depolarization by either activating K+ currents or inhibiting Ca2+ currents, although other mechanisms have been proposed. We have directly measured intracellular Ca2+ concentrations of giant pre-synaptic terminals in the chick ciliary ganglion. We report here that adenosine inhibited the nerve-evoked Ca2+ influx in the terminal by activating A1 receptors. Reduced Ca2+ influx was due largely to inhibition of omega-conotoxin GVIA-sensitive Ca2+ channels in the presynaptic terminal.

Adenosine↗
PubMed1993

Re-evaluation of calcium currents in pre- and postsynaptic neurones of the chick ciliary ganglion.

1. Presynaptic nerve terminals of ciliary ganglia of the chick embryo were identified by the accumulation of dextran-tetramethylrhodamine applied to the cut end of the oculomotor nerve. Ca2+ currents were then recorded from the identified nerve terminals. 2. Whole-cell recordings were carried out simultaneously from a presynaptic terminal and its postsynaptic cell. The generation of presynaptic Ca2+ currents induced a postsynaptic response with a short delay. Electrical coupling was present in eight of fifteen pairs. The coupling ratio did not exceed 5%. 3. High-threshold Ba2+ currents were observed in presynaptic terminals without any evidence for the presence of low-threshold Ca2+ channels. The Ba2+ current was completely blocked by 50 microM Cd2+. 4. The presynaptic Ca2+ current induced by a long depolarizing pulse showed inactivation, but this inactivation was diminished when Ca2+ was replaced with Ba2+. 5. The presynaptic Ba2+ current was insensitive to dihydropyridines (DHPs). omega-Conotoxin GVIA (omega CgTX) suppressed a large fraction of the Ba2+ current irreversibly. About 10% of the Ba2+ current was resistant to both DHPs and omega CgTX. 6. The omega CgTX-sensitive component was not sensitive to changes in the holding potential between -120 and -50 mV. The omega CgTX-resistant component tended to be inactivated at depolarized holding potentials. 7. In some perisynaptic Schwann cells, small Ca2+ currents were observed. These Ca2+ currents increased monotonically with depolarization. 8. Only high-threshold Ca2+ channel currents were observed in postsynaptic ciliary cells. Exposure to 50 microM Cd2+ completely abolished the Ca2+ current. 9. About 25% of the Ba2+ currents were blocked by nifedipine (10 microM) in ciliary cells. The nifedipine-resistant component was partly blocked by omega CdTX (10 microM) leaving a small component (about 20%) which was resistant to both nifedipine and omega CgTX. 10. In ciliary cells, the fraction of Ba2+ currents blocked by omega CgTX was not affected by the presence or absence of nifedipine. Similarly, nifedipine blocked the Ba2+ currents to the same extent whether omega CgTX was present or not. The Ba2+ currents potentiated by Bay K 8644 were eliminated by nifedipine. 11. It is concluded that the presynaptic terminal of chick ciliary ganglion did not possess DHP-sensitive Ca2+ channels in contrast with the postsynaptic cell. Two subpopulations of presynaptic Ca2+ channels were distinguishable by their sensitivity to omega CgTX and membrane potential.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1993

An improved method for perforated patch recordings using nystatin-fluorescein mixture.

This paper describes an improved method for solubilizing nystatin in an aqueous solution without the aid of organic solvents. The patch pipette was filled with a solution of nystatin and fluorescein sodium mixed in a molar ratio of 1:10. The success rate of perforated patch recordings was substantially improved, and the access resistance of 20-40 M omega was readily achieved.

Action Potentials↗