Membrane current responses of NG108-15 mouse neuroblastoma x rat glioma hybrid cells to bradykinin.
1. Membrane current responses to focal application of bradykinin (BK) were recorded in voltage-clamped NG108-15 neuroblastoma x glioma hybrid cells. 2. BK produced sequential outward and inward currents at clamp potentials between -60 and -30 mV, designated IBK(out) and IBK(in), respectively. 3. The outward current IBK(out) was accompanied by an increased membrane conductance. Ramp current-voltage (I-V) curves yielded a reversal potential (VBK) of -80 +/- 5.6 mV (mean +/- S.D., n = 9) in 5.4 mM [K+]o. VBK showed a positive shift on raising [K+]o, compatible with a primary increase in K+ conductance. Subtracted I-V curves indicated that the underlying conductance was not strongly voltage dependent between -120 and -40 mV. 4. IBK(out) was inhibited by d-tubocurarine (dTC, 0.1-0.5 mM) but was insensitive to tetraethylammonium (TEA) below 5 mM. 5. The inward current IBK(in) was accompanied by a fall in membrane conductance. This was associated with the inhibition of a time- and voltage-dependent K+ current, IM. In consequence, IBK(in) was strongly voltage dependent and dissipated, usually without reversal, on hyperpolarizing the cell beyond -70 mV in 5.4 mM [K+]o. Reversal to an outward current negative to -40 mV could be obtained on raising [K+]o to 54 mM. 5. Both IBK(in) and IBK(out) persisted when ICa was blocked with Co2+ or Cd2+. IBK(out) slowly diminished in Ca2+-free, Mg2+-substituted solution. 6. The Ca2+ spike current ICa and the Ca2+-activated K+ current IAHP were inhibited during IBK(out) or after Ca2+ injections. BK did not affect the voltage-activated K+ current IK(V) recorded in Co2+ solution. 7. It is concluded that the dual response to BK results from opposing effects on two different species of K+ current. IBK(out) results from activation of a Ca2+-dependent, voltage-insensitive K+ conductance, probably mediated by a transient rise in intracellular Ca2+. It is suggested that the Ca2+ is released from an intracellular store. IBK(in) results primarily from inhibition of the Ca2+-independent, voltage-gated K+ current, IM. This effect is not replicated by a rise of intracellular Ca2+ and must therefore be generated by another mechanism.
Brown
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DA
Laboratory of Cell Biology, National Institute of Mental Health, Bethesda, MD 20892.
Higashida
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D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001464:Barium / Q000494:pharmacology; D001920:Bradykinin / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology; D002460:Cell Line; D003035:Cobalt / Q000494:pharmacology; D006822:Hybrid Cells / Q000502:physiology*; D007473:Ion Channels / Q000502:physiology*; D016210:Methacholine Chloride; D008688:Methacholine Compounds / Q000494:pharmacology; D051379:Mice; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D014403:Tubocurarine / Q000494:pharmacology
D007473:Ion Channels; D008688:Methacholine Compounds; D013757:Tetraethylammonium Compounds; D016210:Methacholine Chloride; D001464:Barium; D003035:Cobalt; D019789:Tetraethylammonium; D011188:Potassium; D001920:Bradykinin; D002118:Calcium; D014403:Tubocurarine