Noradrenaline-evoked cation conductance recorded with the nystatin whole-cell method in rabbit portal vein cells
1. Noradrenaline-evoked currents were studied with the perforated patch technique (nystatin in the patch pipette) in freshly dispersed rabbit portal vein cells. 2. With potassium-containing solutions noradrenaline produced an inward current at -50 mV and an outward current (IK(Ca] at 0 mV. In potass...
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Published in | The Journal of physiology Vol. 435; no. 1; pp. 21 - 39 |
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Main Authors | , |
Format | Journal Article |
Language | English |
Published |
Oxford
The Physiological Society
01.04.1991
Blackwell |
Subjects | |
Online Access | Get full text |
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Summary: | 1. Noradrenaline-evoked currents were studied with the perforated patch technique (nystatin in the patch pipette) in freshly
dispersed rabbit portal vein cells. 2. With potassium-containing solutions noradrenaline produced an inward current at -50
mV and an outward current (IK(Ca] at 0 mV. In potassium-free conditions noradrenaline elicited two distinct membrane currents
which could be differentiated according to their sensitivity to the presence of caffeine in the bathing solution. One current
was blocked whereas the second response was unaffected by caffeine. 3. The reversal potential (Er = -2.0 mV) of the caffeine-sensitive
current was altered when external chloride was replaced with more permeant anions but Er was not changed when external sodium
was replaced by Tris. Therefore the caffeine-sensitive current appears to be a calcium-activated chloride current (ICl(Ca].
4. Er (+6.0 mV) of the caffeine-insensitive current was not altered by anion substitution but was changed when external sodium
was replaced by Tris and barium ions. Thus the caffeine-insensitive conductance is a non-selective cation current (Icat).
5. When external NaCl was replaced by BaCl2, Er was shifted to more positive potentials which suggests that the cation conductance
is more permeable to barium than to sodium. Icat was not affected by 10(-6) M-nifedipine. 6. The steady-state current-voltage
relationship was linear between -50 and +50 mV for ICl(Ca) but the cation conductance mechanism displayed pronounced inward
rectification and little outward current flowed across the membrane at positive potentials. 7. Caffeine (which releases calcium
from internal stores) and the calcium ionophore ionomycin, which are expected to increase intracellular calcium concentration,
evoked ICl(Ca) but not Icat. Thus ICl(Ca) but not Icat can be activated directly by an increase in intracellular calcium concentration.
8. When calcium was removed from the bathing solution the amplitude of Icat was not altered at early times in Ca(2+)-free
conditions but was abolished after 10 min. Icat was readily activated by noradrenaline in the presence of ionomycin, which
inactivated ICl(Ca). A permissive role for calcium in the generation of Icat is suggested. 9. The times between the application
of noradrenaline and the onset of the chloride and cationic conductances were similar (0.75 and 0.9 s respectively). In contrast
the rise time (3.9 s) and half-decay time (11 s) of Icat were much longer than the corresponding values of ICl(Ca) (respectively
1.9 and 2 s). In high-barium solution noradrenaline sometimes evoked a response that lasted for up to 10 min. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.1991.sp018496 |