omega-agatoxin-iva and calciseptine

1. In this study, intracellular Ca(2+) was measured as the Fura-2 ratio (R) of fluorescence excited at 340 and 380 nm (F(340)/F(380)) in nonpressurized rat mesenteric small arterioles ( (lumen diameter) 10-25 microm). 2. The response to depolarization using 75 mm KCl was an increase in R from a baseline of 0.96+/-0.01 ([Ca(2+)](i) approximately 74 nm) to 1.04+/-0.01 ( approximately 128 nm) (n=80). The response to 75 mm K(+) was reversibly abolished in Ca(2+)-free physiological saline solution, whereas phentolamine (10 microm) or tetrodotoxin (1 microm) had no effects. LaCl(3) (200 microm) inhibited 61+/-9% of the response. 3. A [K(+)]-response curve indicated that the Ca(2+) response was activated between 15 and 25 mm K(+). The data suggest that the Ca(2+) response was caused by the activation of voltage-dependent Ca(2+) channels. 4. Mibefradil use dependently inhibited the Ca(2+) response to 75 mm K(+) by 29+/-2% (100 nm), 73+/-7% (1 microm) or 89+/-7% (10 microm). Pimozide (500 nm) use dependently inhibited the Ca(2+) response by 85+/-1%. 5. Nifedipine (1 microm) inhibited the Ca(2+) response to 75 mm K(+) by 41+/-12%. The response was not inhibited by calciseptine (500 nm), omega-agatoxin IVA (100 nm), omega-conotoxin MVIIA (500 nm), or SNX-482 (100 nm). 6. Using reverse transcriptase-polymerase chain reaction, it was shown that neither Ca(V)2.1a (P-type) nor Ca(V)2.1b (Q-type) voltage-dependent Ca(2+) channels were expressed in mesenteric arterioles, whereas the Ca(V)3.1 (T-type) channel was expressed. Furthermore, no amplification products were detected when using specific primers for the beta(1b), beta(2), or beta(3) auxiliary subunits of high-voltage-activated Ca(2+) channels. 7. The results suggest that the voltage-dependent Ca(2+) channel activated by sustained depolarization in mesenteric arterioles does not classify as any of the high-voltage-activated channels (L-, P/Q-, N-, or R-type), but is likely to be a T-type channel. The possibility that the sustained Ca(2+) influx observed was the result of a T-type window current is discussed.

Topics: Animals; Arterioles; Blotting, Southern; Calcium; Calcium Channels; Denmark; Elapid Venoms; Fluorescence; Fura-2; Gene Expression; Lanthanum; Male; Membrane Potentials; Mesenteric Arteries; Mibefradil; Muscle, Smooth, Vascular; Nifedipine; omega-Agatoxin IVA; omega-Conotoxins; Phentolamine; Pimozide; Potassium Chloride; Rats; Rats, Wistar; Reverse Transcriptase Polymerase Chain Reaction; Sodium-Calcium Exchanger; Solutions; Spider Venoms; Tetrodotoxin

Our aim was to investigate the possible involvement of spinal voltage-dependent Ca(2+) channels (VDCCs) in vincristine-induced hyperalgesia and also to characterize this hyperalgesic state in the spinal cord. Mice receiving vincristine displayed significantly lower mechanical nociceptive thresholds than controls. Intrathecal omega-conotoxin GVIA (an N-type blocker) produced dose-dependent inhibition of the mechanical nociception, its antinociceptive effect being greater in vincristine-treated mice than in controls. The antinociception of omega-agatoxin IVA (a P/Q-type blocker) and calciseptine (an L-type blocker) were both slightly, but not significantly greater in vincristine-treated mice. An N-methyl-D-aspartate-receptor antagonist but not a tachykinin-NK1-receptor antagonist produced greater antinociception in vincristine-treated mice. These results suggest that vincristine-induced hyperalgesia involves a sensitization of the spinal processing of mechanical sensory information via a mechanism involving N-type but not P/Q- or L-type VDCCs. A spinal glutamatergic pathway also appears to be involved in this hyperalgesia.

Topics: Animals; Antineoplastic Agents, Phytogenic; Calcium Channel Blockers; Calcium Channels; Dose-Response Relationship, Drug; Elapid Venoms; Hyperalgesia; Male; Mice; Neurokinin-1 Receptor Antagonists; omega-Agatoxin IVA; omega-Conotoxins; Pain Measurement; Pain Threshold; Quinuclidines; Receptors, N-Methyl-D-Aspartate; Spinal Cord; Time Factors; Valine; Vincristine

Previously, we have presented evidence for the presence of L-type voltage-dependent Ca2+ channels (VDCC) in 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, (acetoxymethyl)ester (BAPTA-AM)-incubated motor nerve terminals (MNTs) of the levator auris muscle of mature mice. The aim of the present work was to study the coupling of these L-type VDCC to neurotransmitter release by inhibiting protein phosphatases. We thus studied the effects of the protein phosphatase inhibitors okadaic acid (OA) and pervanadate on quantal content (QC) of transmitter release with the P/Q-type channels fully blocked. The QC was not significantly different under the three experimental conditions tested: incubation with dimethylsulphoxide (DMSO), ethylene-glycol-bis(beta-aminoethylether)-N,N,N',N'-tetraacetic acid, (acetoxymethyl)ester (EGTA-AM) and BAPTA-AM. After preincubation with OA (1 microM), but not with pervanadate, QC increased substantially in the BAPTA-AM-incubated (up to 400%) MNT, but not in those incubated with DMSO or EGTA-AM. The OA-induced increment of QC was attenuated greatly (approximately 95% reduction) by preincubation with either nitrendipine (10 microM) or calciseptine (300 nM). The effect of OA (1 microM) and pervanadate (0.1 mM) on spontaneous neurotransmitter release was also studied. After preincubation with OA, but not per-vanadate, miniature end-plate potential (MEPP) frequency increased only in the BAPTA-AM-incubated MNT (up to 700% increment). This response was attenuated (by approximately 80%) by nitrendipine (10 microM) or calciseptine (300 nM). In contrast, neither omega-agatoxin IVA (120 nM) nor omega-conotoxin GVIA (1 microM) affected this OA-induced increment significantly. We also evaluated the relationship between QC and extracellular [Ca2+] ([Ca2+]o) in BAPTA-AM-incubated MNT. Under conditions in which only P/Q-type VDCC were available to participate in neurotransmitter release, QC increased as [Ca2+]o was raised from 0.5 to 2 mM. However, when only L-type VDCC were available, QC increased when [Ca2+]o increased from 0.5 to 1 mM, but decreased significantly at 2 mM. The mean latency for P/Q-type VDCC-mediated EPP was 1.7-1.9 ms; for L-type VDCC-mediated EPP, 1.9-2.5 ms. The rise time of the L-type VDCC mediated EPP was significantly slower than that mediated by P/Q-type VDCC. Preincubation with H-7 (100 microM), a potent inhibitor of protein kinase C (PKC) and adenosine 3',5'cyclic monophosphate (cAMP)-dependent protein kinase (PKA)

Topics: Animals; Buffers; Calcium; Calcium Channel Blockers; Calcium Channels, L-Type; Chelating Agents; Egtazic Acid; Elapid Venoms; Enzyme Inhibitors; Evoked Potentials; Ionophores; Mice; Motor Endplate; Motor Neurons; Muscle, Skeletal; Neurotransmitter Agents; Nitrendipine; Okadaic Acid; omega-Agatoxin IVA; omega-Conotoxin GVIA; Presynaptic Terminals; Synaptic Transmission; Vanadates