Characterization of functional responses in A9 cells transfected with cloned rat 5-HT1C receptors.
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/l) 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/l) 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/l), apamin (0,5 mumol/l) and 4-aminopyridine (5 mmol/l). 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/l) 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.(ABSTRACT TRUNCATED AT 250 WORDS)
Boddeke
H W
HW
Sandoz Pharma Ltd, Preclinical Research, Basle, Switzerland.
Hoffman
B J
BJ
Palacios
J M
JM
Knot
H
H
Hoyer
D
D
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D003001:Cloning, Molecular; D019204:GTP-Binding Proteins / Q000502:physiology; D007424:Intracellular Fluid / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D011188:Potassium / Q000378:metabolism; D051381:Rats; D011985:Receptors, Serotonin / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection
D011985:Receptors, Serotonin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D012701:Serotonin; D019204:GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium; D002118:Calcium