Potentiation by stannous chloride of calcium entry into osteoblastic MC3T3-E1 cells through voltage-dependent L-type calcium channels.

The present study was undertaken to confirm that L-type Ca(2+) channels are involved in Ca(2+) entry into osteoblastic MC3T3-E1 cells and to examine the effect of SnCl2, a Ca(2+)]-channel activator, on the intracellular Ca(2+)concentration ([Ca(2+)]i). High K(+)concentration-dependently raised the [Ca(2+)]i. All of the L-type Ca(2+)channel blockers used here, such as nifedipine, nicardipine, verapamil, and diltiazem, and CdCl2 (a non-selective blocker) inhibited the high K(+)-induced [Ca(2+)]i rise, but v-conotoxin GVIA (an N-type blocker) and NiCl2(a T-type blocker) had no effect. Application of SnCl2 alone did not change the [Ca(2+)]i. However, in the presence of high K(+), SnCl2 enhanced the high K(+)-induced [Ca(2+)]i rise, which was inhibited by Ca(2+)]-free medium or nifedipine. In the case where high K(+)was applied prior to SnCl2, SnCl2 alone raised the [Ca(2+)]i by itself. In conclusion, MC3T3-E1 cells possess the voltage-dependent L-type Ca(2+)] channels and SnCl2 facilitates the Ca(2+) entry through the L-type ones under the condition of the membrane depolarization. There is the possibility that Ca(2+) release from intracellular Ca(2+) stores is involved in the action of SnCl2.

Enhancement of dopamine release by propylene glycol in PC12 cells.

Propylene glycol (PG) is widely used as a solvent for injections. However, there are a few reports describing severe toxic effects of PG on human nervous tissues. To elucidate its mechanism, the present study has been conducted to determine whether PG enhances the release of catecholamine in PC12 cells. When the incubation time was longer than 3 min, PG significantly facilitated the dopamine release. PG (0.2-20 %v/v) concentration-dependently increased the dopamine release and the effects of PG at the concentrations above 1% were significant. High K+ (50 mM) and carbamylcholine (50 microM) increased the dopamine release. High K+ and electrical stimulation augmented the action of PG. Tetrodotoxin (1 microM) had no effect on the PG action. In conclusion, PG enhances the dopamine release. It is suggested that the facilitation of the transmitter release from the motor nerve terminals may be related to the PG-evoked skin twitch.

Rise in intracellular calcium concentration by propylene glycol in PC12 cells.

In order to elucidate the mode of excitatory actions of propylene glycol (PG) on nervous tissues, intracellular calcium concentration ([Ca2+]i) of PC12 cells was measured on the video-imaging analysis system with fura-2. PG concentration-dependently (0.1-20%v/v) raised the [Ca2+]i. Hexamethonium and d-tubocurarine inhibited the carbamylcholine-induced [Ca2+]i rise, but these blockers had no effect on PG. High K+ potentiated the action of PG. The extent of the rise induced by PG in the differentiated cells was larger than that in the undifferentiated ones. The findings suggest that the rise in [Ca2+]i is involved in the excitatory effects of PG.

Facilitation of calcium influx by propylene glycol through the voltage-dependent calcium channels in PC12 cells.

Propylene glycol (PG) raises an intracellular calcium concentration ([Ca2+]i) in PC12 cells. The present study has been undertaken to examine whether or not the voltage-dependent Ca2+ channels are involved in the PG-induced rise in [Ca2+]i and, if so, to determine which types participate in it. CdCl2 (50 micro M) and the Ca2+ -free saline depressed the action of PG (0.5 - 10 %v/v)-induced [Ca2+]i rise. Although NiCl2 (50 micro M) at the same concentration as CdCl2, and omega-agatoxin (50 and 300 nM) had no effect on the PG-induced [Ca2+]i rise, each of omega-conotoxin (1 micro M), nifedipine (10 micro M), nicardipine (10 micro M), varapamil (10 micro M) and diltiazem (10 micro M) significantly decreased it. Electrical stimulation and Bay K 8644 (1 micro M) enhanced the PG-induced [Ca2+]i rise. The second phase of the [Ca2]i rise was fallen fast by nicardipine (10 micro M), but not by omega-conotoxin (1 micro M). The results obtained suggested that the Ca2+ influx through the L- and N-type Ca2+ channels are involved in the PG-induced [Ca2+]i rise.

Facilitation of mouse neuromuscular transmission by propylene glycol.

Propylene glycol (PG) has an excitatory effect on the skeletal muscle of the frog. To determine whether PG has a facilitating effect on the neuromuscular transmission of the mammalian as well as on that of the amphibian and to elucidate the mode of action, we have investigated the effects of PG on the neuromuscular junction of the mouse. PG (1.0% v/v) significantly increased the amplitude of endplate potential. PG raised the frequency of miniature endplate potential and increased its amplitude. PG increased the mean quantal content of the endplate potential. These results indicate that PG facilitates the mouse neuromuscular transmission by accelerating the transmitter release from the nerve terminals and by raising the acetylcholine sensitivity of the endplates.

Augmentation of calcium influx by stannous chloride at mouse motor nerve terminals.

Stannous chloride (SnCl2) facilitates the calcium (Ca) entry into the frog motor nerve terminals. To compare the mode of action of SnCl2 on the Ca channels in the mouse with that in the frog, we investigated the effects of SnCl2 on the inward Ca current at the nerve terminals. SnCl2 (0.1 mM) did not change the second positive component of the action potential (an outward potassium (K) current) at the terminal part of the nerve terminal. SnCl2 (0.1 mM) increased the amplitude of the prolonged negative or positive deflection (an inward Ca current) evoked by treatment with 1 mM tetraethylammonium and 0.1 mM 3,4-diaminopyridine at the terminal or preterminal part of the nerve terminal, respectively. This augmenting effect of SnCl2 was inhibited by cumulative addition of Ca channel blockers, i.e., 0.1 mM CdCl2, 5 mM NiCl2, 5 mM CoCl2, 5 mM MnCl2, or 10 mM MgCl2. From the results obtained, it has been confirmed that SnCl2 facilitates the transmitter release by enhancing the Ca influx at the nerve terminals but not by blocking the K channels and that the mode of action of SnCl2 in the mouse is identical with that in the frog.

Facilitation of transmitter release from mouse motor nerve terminals by stannous chloride.

Although a mixture composed of 30 microM stannous chloride (SnCl2) and 75 microM tartaric acid (TA) facilitates neuromuscular transmission in the frog, the mixture had no effect on the endplate potential (e.p.p.) in the rat. The present study has been undertaken to determine whether the responses of the mouse (mammalian) to SnCl2 are different from those of the frog (amphibian). The mixture had no effect on the resting potential or the membrane resistance of the muscle fiber. The mixture did not change the e.p.p. amplitude, but TA (75 microM) significantly decreased it. The mixture increased the quantal content of the e.p.p., but TA decreased it. The mixture raised the frequency of the miniature endplate potential (m.e.p.p.) in the high potassium-medium. In normal saline, both the mixture and TA decreased both the m.e.p.p. frequency and its amplitude. These results suggest that SnCl2 itself facilitates the transmitter release from nerve terminals in the mammalian as well as in the amphibian species.

Propylene glycol-induced skeletal muscle excitation.

The effects of propylene glycol (PG) on frog nerve-muscle preparations were examined to determine whether it has an effect on neuromuscular transmission and, if so, to elucidate the mode of the action. PG (5%, v/v) increased the twitch tension to over twice the control value. PG at concentrations above 0.2% significantly increased the amplitude of the endplate potential. PG (1%) raised the frequency of the miniature endplate potentials and increased their amplitude. These results show that PG both facilitates transmitter release from the nerve terminals and raises the acetylcholine sensitivity of the muscle endplate.

Interaction between stannous chloride and calcium channel blockers in frog neuromuscular transmission.

We have investigated the interactions between stannous chloride (SnCl2) and calcium (Ca) channel blockers on endplate potentials (e.p.p.) and on miniature endplate potentials (m.e.p.p.) to determine which type of channel (among L-, N-, and T-type) participates in the SnCl2-induced increase in Ca entry into motor nerve terminals. The e.p.p. amplitude augmented by 30 microM SnCl2 was decreased by cumulative addition of 10 microM CdCl2 or 0.5 microM omega-conotoxin but not by 10 microM NiCl2 or 5 microM nicardipine. The SnCl2 (30 microM)-induced rise in m.e.p.p. frequency in high-potassium medium was reduced by 0.5 microM omega-conotoxin but not by 5 microM nicardipine. These results suggest that activation of the N-type Ca channel is involved in the SnCl2-induced increase in Ca entry into the nerve terminals.

Activation of N-type calcium channels by stannous chloride at frog motor nerve terminals.

Stannous chloride (SnCl2) increases the calcium (Ca) entry into motor nerve terminals through the voltage-dependent Ca channels. The present study has been conducted to determine which type of channel (i.e., L-, N-, or T-type) participates in the Ca entry increased by SnCl2 (0.1 mM)-induced enhancement of the inward Ca current was more strongly inhibited by CdCl2 (50 microM) or omega-conotoxin (0.1 microM) than by NiCl2 (50 microM) or nifedipine (10 microM), respectively. From the results obtained, it is concluded that SnCl2 increases the Ca entry into the nerve terminal by activating the N-type Ca channels.

Evidence for enhancement of calcium inward current by stannous chloride at frog motor nerve terminals.

Effects of stannous chloride (SnCl2, 30-100 microM) on presynaptic currents recorded from frog neuromuscular junctions were investigated to confirm that increased calcium entry is involved in SnCl2-induced facilitation of the evoked transmitter release. After the potassium channel was blocked by tetraethylammonium (0.1 mM) and 3,4-diaminopyridine (10 microM), SnCl2 (0.1 mM) augmented the prolonged positive deflection of the presynaptic action potential ascribable to calcium inward current, which was thereafter suppressed by the addition of cadmium (0.1 mM). These results suggest that SnCl2 enhances the calcium inward current at the motor nerve terminals.

Participation of calcium ions in stannous chloride-induced facilitation of transmitter release from frog motor nerve terminals.

To determine whether Ca2+ participates in the augmentative action of SnCl2 on the transmitter release, we have investigated interactions between SnCl2 and Cd2+, verapamil, or low Ca2+ on endplate potentials (e.p.p.) and have compared the effect of SnCl2 with that of Mg2+ on miniature endplate potentials (m.e.p.p.). SnCl2 increased the e.p.p. amplitude dose-dependently. Cd2+, verapamil and low Ca2+ shifted the dose-response relationship between SnCl2 and the e.p.p. downwards. In contrast to Mg2+, SnCl2 increased the m.e.p.p. frequency with raised K+ concentration in the medium. These results suggest that Ca2+ participates in the SnCl2-induced facilitation of the transmitter release and that SnCl2 enhances the Ca2+ entry into the nerve terminals.

Stannous chloride-induced increase in calcium entry into motor nerve terminals of the frog.

The effects of SnCl2 on potentials recorded extracellularly from motor nerve terminals of the bullfrog were studied to elucidate the mechanism of the SnCl2-induced facilitation of evoked transmitter release. Under conditions in which the muscle preparations were pretreated with d-tubocurarine and tetraethylammonium in a K+-free medium, SnCl2 (50 microM) augmented the prolonged positive deflection ascribed to the inward Ca2+ current, an effect which was reduced by addition of Cd2+. The results suggest that SnCl2 could increase Ca2+ entry into the nerve terminals.

Stannous ion-induced tetanic contraction of the frog sartorius muscle.

Present study was conducted to elucidate the mechanism of twitch augmentation by stannous ion. Stannous ion increased the amplitude of the endplate potential and moreover, generated repetitive firing of the muscle fiber. These findings suggest that the twitch augmentation by stannous ion may be due not only to recruitment of the muscle fibers but also to a brief tetanic contraction of the individual fibers.

Acceleration by stannous ion of the evoked release of transmitter from motor nerve endings in the frog.

Stannous ion (Sn2+, 30 microM) increased the amplitude of endplate potential (EEP) in the frog sartorius muscle, although the amplitude of miniature endplate potential (MEPP) or acetylcholine potential evoked by iontophoretic application of acetylcholine was unchanged. Sn2+ (10-100 microM) dose-dependently increased the quantal content of the EPP. MEPP frequency was not altered by 30 microM Sn2+. These findings indicate that Sn2+ may increase the EPP as a result of acceleration of the transmitter release evoked by nerve impulses.

Anti-curare action of stannous ion in the frog neuromuscular junction.

For the purpose of elucidating the mechanism of action of stannous ion (Sn2+), we investigated effects of stannous chloride (SnCl2) on the twitch and on the electrical phenomena in the muscle fiber. Sciatic nerve-sartorius muscle preparations from the bullfrog were used as the material. Effect of SnCl2 was examined on the twitch partially inhibited by pretreatment with d-tubocurarine. SnCl2 (1-100 microM) antagonized d-tubocurarine and enhanced the twitch dose-dependently. Tartaric acid, which is the solvent used for SnCl2 solution, had no augmentative effect on the twitch, even at a concentration as high as 250 microM. SnCl2 (1-50 microM) increased the amplitude of the endplate potential; that is, it exerted an anti-curare action. The resting potential and the membrane resistance of the muscle fiber were not altered by 30 microM SnCl2. These findings lead to the conclusion that Sn2+ enhances the twitch by increasing the endplate potential of the muscle fibers.

Facilitation of frog neuromuscular transmission by sodium fluoride.

1. The effects of sodium fluoride (NaF, 5 mM) alone or in combination with theophylline (1.5 mM) or imidazole (1.5 mM) on the amplitude of the endplate potential (e.p.p.), frequency of the miniature endplate potential (m.e.p.p.), and the quantal content of the e.p.p. of bullfrog muscle were investigated. The effects of forskolin (1 microM) and papaverine (1 microM) on the m.e.p.p. frequency were also studied. 2. NaF caused an increase of 22% in the amplitude of the e.p.p. This NaF-induced increase was enhanced by theophylline (to 51%) and reduced by imidazole (to 10%). 3. Papaverine (0.1-3 microM) increased the frequency of m.e.p.ps. Forskolin at 1 microM raised the m.e.p.p. frequency by 13%. The effect was increased to 31% by 1 microM papaverine. NaF also raised the m.e.p.p. frequency by 90%. This action too was increased by theophylline (2.6 fold) and by papaverine (2.1 fold); however, it was reduced by imidazole (1.3 fold). 4. NaF increased the quantal content of the e.p.p. by 28%. This effect was enhanced by theophylline to 44%, while it was diminished by imidazole. 5. These results suggest that an increase in the transmitter release via an elevation of cyclic AMP may be involved in the facilitation of neuromuscular transmission by NaF.

Enhancement of the twitch of bull frog sartorius muscle by fluorides.

Effects of 5 kinds of fluorides on the twitch of the sartorius muscle of the bull frog were investigated. All of the fluorides (0.1-2.0 mM) enhanced the twitch evoked by nerve stimulation. The extents of enhancement at 2.0 mM were in the order: stannous fluoride much greater than potassium fluoride greater than sodium silico fluoride greater than sodium fluoride greater than diammine silver fluoride. The extent of each enhancement was larger than that in the case of direct stimulation of the muscle. These findings show that fluorides commonly enhance the twitch of skeletal muscle and that the extent of enhancement is related to the properties of cations included in the fluoride.

Arsenic excretion after treatment of arsenic poisoning with DMSA or DMPS in mice.

The effects of 2,3-dimercaptosuccinic acid (DMSA) and 2,3-dimercaptopropane-1-sulfonic acid, Na salt (DMPS) on arsenic excretion in arsenic poisoning were studied using ICR mice. One group of mice was given arsenic trioxide (5 mg As/kg, s.c.) and another two groups were given DMSA or DMPS (100 mg/kg, i.p.) immediately after administration of the arsenic (5 mg/kg, s.c.). Arsenic excretion in urine and feces was determined by atomic absorption spectrophotometry. Results obtained showed a marked arsenic excretion in the urine collected at the first 12 hr in the group treated with DMSA. Further remarkable arsenic excretion in the feces was seen in the group treated with DMPS, suggesting that arsenic might have been excreted in the bile.