CHARACTERIZATION OF FUNCTIONAL-RESPONSES IN A9-CELLS TRANSFECTED WITH CLONED RAT 5-HT1C RECEPTORSBODDEKE, HWGM., HOFFMAN, BJ., PALACIOS, JM., KNOT, H. & HOYER, D., Feb-1993, In : Naunyn-Schmiedebergs Archives of Pharmacology. 347, 2, p. 119-124 6 p.
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Functional responses to stimulation of rat 5-HT1C receptors expressed in A9 cells were studied using whole cell voltage clamp and calcium recording techniques. Stimulation of 5-HT1C receptors evoked outward currents clamped at - 50 mV. The outward currents were reduced when GTP was excluded from the intracellular recording solution or when GDP-beta-S was added.
8-Bromo cyclic AMP (5 mmol/1) neither produced an effect per se nor affected the 5-HT-induced outward current in A9 cells, thus excluding cAMP as a second messenger involved in 5-HT1C receptor activation. Phorbol myristic acetate (PMA; 10 mumol/1) did not affect the electrical activity of the transfected A9 cells but reduced the 5-HT-induced current amplitude to 71+/-9% of the control value (n = 12). This indicates that activation of protein kinase C does not play a direct role in the 5-HT-induced response in these cells.
The 5-HT induced currents mainly involved potassium ions, although a small contribution of chloride ions was also observed. The 5-HT-induced current was inhibited by the K+ channel blocking agents tetraethylammonium (1 mmol/1), apamin (0,5 mumol/1) and 4-aminopyridine (5 mmol/1). The 5-HT-induced currents recorded at - 50 mV were unaffected by removal of extracellular calcium, but inclusion of the calcium chelator BAPTA (5 mmol/1) in the intracellular solutions abolished the current. Measurement with the calcium indicator Fluo-3 revealed a 5-HT-induced increase in intracellular calcium which was not affected by removal of extracellular calcium but declined after repeated stimulation.
Determinated of pD2 and K(B) values of several 5-HT ligands using Fura-2 calcium measurements confirmed the pharmacology of the 5-HTc receptor.
The results show that cloned rat 5-HT1C receptors expressed in A9 cells activate a calcium-dependent potassium conductance.
|Number of pages||6|
|Journal||Naunyn-Schmiedebergs Archives of Pharmacology|
|Publication status||Published - Feb-1993|
- 5-HT1C RECEPTORS, A9 CELLS POTASSIUM CONDUCTANCE, CALCIUM RESPONSE, FURA-2 FLUO-3, <H-3>5-HYDROXYTRYPTAMINE BINDING-SITES, PIG CHOROID-PLEXUS, INOSITOL 1,4,5-TRISPHOSPHATE, XENOPUS OOCYTES, CELLS, CDNA, TRISPHOSPHATE, INDICATORS, LIGANDS, BRAIN