Effects of propofol and pentobarbital on calcium concentration in presynaptic boutons on a rat hippocampal neuron.

PURPOSE: Numerous reports suggest that intravenously administered (IV) anesthetics affect postsynaptic events in the central nervous system. However, there is little evidence about how general anesthetics influence the presynaptic processes. The level of presynaptic calcium (Ca(2+)) concentration ([Ca(2+)](pre)) regulates neurotransmitter release. In this study, we investigated the effects of anesthetic propofol IV and the barbiturate pentobarbital on neurotransmitter release by measuring [Ca(2+)](pre) in the presynaptic nerve terminals (boutons) on a dissociated single hippocampal rat neuron. METHODS: Sprague-Dawley rats 10-14 days old were decapitated under pentobarbital anesthesia, and brain slices were prepared. The hippocampal CA1 area was touched with a fire-polished glass pipette, which vibrated horizontally, and neurons were dissociated, along with the attached presynaptic boutons. The presynaptic boutons were visualized under a confocal laser-scanning microscope after staining with FM1-43 dye, and [Ca(2+)](pre) was measured with acetoxymethyl ester of fluo-3 (fluo-3 AM). RESULTS: High potassium (K(+)) (15-90 mM) increased the [Ca(2+)](pre) in the Ca(2+)-containing solution in a concentration-dependent manner. Whereas propofol (10 µM) and pentobarbital (300 µM) suppressed the high K(+) (60 mM)-induced increase in [Ca(2+)](pre) in the boutons attached to the dendrite, they did not affect [Ca(2+)](pre) in the boutons attached to the soma or dendrite base. As a large majority of excitatory synapses are located on dendritic spines, these agents may affect Ca(2+) mobilization in the excitatory presynaptic boutons. CONCLUSIONS: Propofol and pentobarbital may affect neurotransmitter release from the excitatory presynaptic nerve terminals due to inhibition of increase in [Ca(2+)](pre).

Effects of methyl p-hydroxybenzoate (methyl paraben) on Ca2+ concentration and histamine release in rat peritoneal mast cells.

1 Mechanisms of methyl p-hydroxybenzoate (methyl paraben) action in allergic reactions were investigated by measuring the intracellular Ca(2+) concentration ([Ca(2+)](i)) and histamine release in rat peritoneal mast cells (RPMCs). 2 In the presence or absence of extracellular Ca(2+), methyl paraben (0.1-10 mM) increased [Ca(2+)](i), in a concentration-dependent manner. Under both the conditions, methyl paraben alone did not evoke histamine release. 3 In RPMCs pretreated with a protein kinase C (PKC) activator (phorbol 12-myristate 13-acetate (PMA) 3 and 10 nM), methyl paraben (0.3-3 mM) induced histamine release. However, a high concentration (10 mM) of the agent did not increase the histamine release. 4 U73122 (0.1 and 0.5 micro M), an inhibitor of phospholipase C (PLC), significantly inhibited the methyl paraben-induced histamine release in PMA-pretreated RPMCs. U73343 (0.5 micro M), an inactive analogue of U73122, did not inhibit the histamine release caused by methyl paraben. 5 In Ca(2+)-free solution, PLC inhibitors (U73122 0.1 and 0.5 micro M, D609 1-10 micro M) inhibited the methyl paraben-induced increase in [Ca(2+)](i), whereas U73343 (0.5 micro M) did not. 6 Xestospongin C (2-20 micro M) and 2 aminoethoxydiphenyl borate (30 and 100 micro M), blockers of the inositol 1,4,5-trisphosphate (IP(3)) receptor, inhibited the methyl paraben-induced increase in [Ca(2+)](i) in Ca(2+)-free solution. 7 In conclusion, methyl paraben causes an increase in [Ca(2+)](i), which may be due to release of Ca(2+) from storage sites by IP(3) via activation of PLC in RPMCs. In addition, methyl paraben possibly has some inhibitory effects on histamine release via unknown mechanisms.

Effects of pentobarbital on purinergic P2X receptors of rat dorsal root ganglion neurons.

Purinergic P2X receptors are ligand-gated ion channels that are activated by extracellular adenosine triphosphate (ATP) and are widely expressed not only in the central and peripheral nervous system but also in tissues throughout the body, playing an important role in the transfer of nociceptive information. Since the influence of barbiturates on P2X receptor subtypes is not known, we studied the effects of pentobarbital sodium (PB) on ATP responses in dorsal root ganglion (DRG) neurons. DRG neurons were dissected from 10- to 14-day-old rats and dissociated after enzyme treatment. Electrical measurements were performed using the nystatin-perforated patch recording mode under voltage-clamp conditions. Drugs were applied using the Y-tube method. ATP evoked three types of inward current at -60 mV: fast desensitizing, slow desensitizing, and mixed. The fast-type current was attributed to activation of P2X3 subtype and the slow type to the P2X2 subtype. PB suppressed the fast-type current in a concentration-dependent manner, while the slow type was slightly reduced. A noncompetitive inhibition was suggested by a downward shift of the ATP concentration-response curves. The current-voltage relationships showed inward rectification, and the extent of suppression was not affected by the holding potential. The reduction was greater in external solutions of higher pH. PB had subtype-specific effects on P2X receptors. The ionized form is likely to be responsible for the suppression of the P2X3 receptor current, which may result in a reduction of the excitability of central and peripheral neurons and may contribute to the anesthetic and analgesic actions of the agent.