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Zolmitriptan stimulates a Ca(2+)-dependent K(+) current in C6 glioma cells stably expressing recombinant human
B Le Grand1, A Panissié, M Perez
1Division of Cardiovascular Diseases, Centre de Recherche Pierre Fabre, 17 Av. Jean Moulin, 81106 Cedex, Castres, France.
Abstract:
Stimulation of a Ca(2+)-dependent K(+) current by zolmitriptan, a 5-HT(1B/1D) receptor partial agonist, was investigated in C6 glioma cells stably expressing recombinant human 5-HT(1B) receptors. Outward K(+) currents (I(K)) were examined in non-transfected C6 glioma cells and in cells expressing cloned human 5-HT(1B) receptors using the patch-clamp technique in the whole-cell configuration. In C6 glioma cells expressing recombinant human 5-HT(1B) receptor, zolmitriptan increased I(K) in a concentration-dependent manner (maximum increase 16.3+/-7.8%, n=5, p<0.001) with a pD(2) value (geometric mean with 95% confidence intervals) of 7.03 (7.90-6.10). Zolmitriptan failed to elicit increases in I(K) in non-transfected C6 cells. In the presence of the mixed 5-HT(1B/1D) receptor antagonist, N-[4-methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2(-methyl-4(5-methyl-1 ,2,4)-oxadiazol-3-yl)[1,1-biphenyl]-4-carboxamide 2HCl (GR 127935, 0. 1 mcM), zolmitriptan (1 mcM) failed to significantly increase I(K) in C6 cells expressing human 5-HT(1B) receptors confirming that zolmitriptan-evoked responses were indeed mediated by human 5-HT(1B) receptors. In C6 cells expressing cloned human 5-HT(1B) receptors, zolmitriptan-induced increases in I(K) were prevented by the calcium chelator, EGTA (5 mM) when included in the patch pipette (maximum increase -3.3+/-4.2%, n=4, P=NS). The Ca(2+)-dependent K(+) channel blockers, iberiotoxin (0.1 mcM) and tetraethylammonium (TEA, 1 mM), abolished zolmitriptan-induced increases in I(K) (4.5+/-7.3%, n=4 and -0.8+/-1.7%, n=4, respectively, P=NS in each case) in C6 cells expressing human 5-HT(1B) receptors, confirming the involvement of Ca(2+)-dependent K(+) channels. In conclusion, the 5-HT(1B/1D) receptor partial agonist, zolmitriptan, stimulates I(K/Ca) in C6 glioma cells stably transfected with human 5-HT(1B) receptors suggesting an increase of hyperpolarizing current.
Insights
Zolmitriptan, a 5-HT(1B/1D) receptor agonist, stimulates calcium-dependent potassium currents (I(K/Ca)) in C6 glioma cells expressing human 5-HT(1B) receptors. This suggests zolmitriptan may increase hyperpolarizing currents via these specific receptors.
Area of Science:
- Neuropharmacology
- Molecular Biology
- Cell Physiology
Background:
- The 5-HT(1B/1D) receptor is a key target for migraine treatment.
- Understanding the downstream signaling pathways of 5-HT(1B/1D) receptor activation is crucial.
- Calcium-dependent potassium currents (I(K/Ca)) play vital roles in cellular excitability.
Purpose of the Study:
- To investigate the effect of zolmitriptan on potassium currents in C6 glioma cells.
- To determine if zolmitriptan-induced currents are mediated by human 5-HT(1B) receptors.
- To elucidate the role of calcium in zolmitriptan's effect on potassium currents.
Main Methods:
- Patch-clamp technique in whole-cell configuration was used to measure outward potassium currents (I(K)).
- Experiments were conducted on non-transfected C6 glioma cells and cells stably expressing human 5-HT(1B) receptors.
- Pharmacological agents including a 5-HT(1B/1D) antagonist (GR 127935), calcium chelator (EGTA), and I(K/Ca) blockers (iberiotoxin, TEA) were utilized.
Main Results:
- Zolmitriptan increased I(K) in a concentration-dependent manner in C6 cells expressing 5-HT(1B) receptors (pD(2) = 7.03).
- No significant increase in I(K) was observed in non-transfected C6 cells or when the 5-HT(1B) receptor antagonist was present.
- Zolmitriptan-induced I(K) increases were abolished by EGTA and specific I(K/Ca) channel blockers, confirming Ca(2+)-dependence.
Conclusions:
- Zolmitriptan stimulates calcium-dependent potassium currents (I(K/Ca)) in C6 glioma cells expressing human 5-HT(1B) receptors.
- The observed effect is specifically mediated by the activation of 5-HT(1B) receptors.
- These findings suggest that zolmitriptan may increase hyperpolarizing currents through 5-HT(1B) receptor signaling.