Regulation by second messengers of the slowly activating, voltage-dependent potassium current expressed in Xenopus oocytes.
1. Voltage-clamp recordings of membrane current were made from Xenopus oocytes that had been injected with RNA which had been transcribed in vitro from a cloned complementary DNA. 2. Depolarization from -80 mV evoked outward potassium currents that developed very slowly. At -20 mV the time constant for activation was about 50 s, and at +40 mV about 6 s. 3. The potassium current was increased by the calcium ionophore A23187 or by intracellular injection of inositol 1,4,5-trisphosphate (IP3), each of which should increase the intracellular calcium concentration ([Ca2+]i). The current was decreased by injection of BAPTA (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid). The current was also reduced by phorbol esters; this effect was blocked by staurosporine. 4. In oocytes that had also been injected with RNA encoding the 5-hydroxytryptamine (5-HT2) receptor, 5-HT increased the potassium current. After caffeine pretreatment, to block the release of intracellular calcium, 5-HT decreased the current; this decrease was prevented by staurosporine. 5. It is concluded that the slowly activating, voltage-dependent potassium current expressed in Xenopus oocytes is increased by increases in [Ca2+]i and is decreased by activation of protein kinase C. Stimulation of 5-HT2 receptors can have both these effects, but the former normally predominates.
Busch
A E
AE
Vollum Institute, Oregon Health Sciences University, Portland 97201.
Kavanaugh
M P
MP
Varnum
M D
MD
Adelman
J P
JP
North
R A
RA
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D004594:Electrophysiology; D009865:Oocytes / Q000502:physiology; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger; D051381:Rats; D011985:Receptors, Serotonin / Q000235:genetics; D012701:Serotonin / Q000502:physiology*; D014982:Xenopus laevis
D015221:Potassium Channels; D012333:RNA, Messenger; D011985:Receptors, Serotonin; D012701:Serotonin; D011188:Potassium; D002118:Calcium