Activation of calcium current in voltage-clamped rat glomerulosa cells by potassium ions
1. We examined Ca2+ influx mechanisms using the whole-cell patch-clamp technique in primary cultures of rat glomerulosa cells. 2. Depolarization of the plasma membrane, as studied by a stepwise or ramp depolarization technique, activated low-threshold, transient (T-type) and high-threshold, long-las...
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Published in | The Journal of physiology Vol. 483; no. Pt 1; pp. 67 - 78 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
England
The Physiological Society
15.02.1995
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Subjects | |
Online Access | Get full text |
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Summary: | 1. We examined Ca2+ influx mechanisms using the whole-cell patch-clamp technique in primary cultures of rat glomerulosa cells.
2. Depolarization of the plasma membrane, as studied by a stepwise or ramp depolarization technique, activated low-threshold,
transient (T-type) and high-threshold, long-lasting (L-type) voltage-dependent calcium channels (VDCCs). 3. Extracellular
K+ activated an inward current (Ig1), even in voltage-clamped cells. This phenomenon was observed within the physiological
concentration range, beginning at 4.6 mM K+o (as opposed to the control level of 3.6 mM K+o). Increased cell conductance and
increased background noise indicated that Ig1 is evoked by enhanced channel activity. Potassium induced no outward current
in the voltage range examined (-120 to +60 mV). 4. When non-permeable anions were present only in the pipette and Na+ and
Mg2+ were omitted from the bath, K+ still activated the current. Ig1 was blocked by 100 microM cadmium but was insensitive
to 2 microM nifedipine or to 300 microM Ni2+. 5. In fluorimetric studies elevation of the cytoplasmic Ca2+ concentration in
response to K+ (5.6-13.6 mM) was reduced only partially when VDCCs were blocked with Ni2+ (200 microM) and nifedipine (2 microM).
6. Elevation of the K+ concentration shifted the threshold potential of the T-type calcium channel in the negative direction.
7. In summary, K+ as a ligand activates Ca(2+)-permeable channels in rat glomerulosa cells. This current may contribute to
the development of Ca2+ signals in response to stimulation with K+ in the physiological range. The reduction of the activation
threshold of the T-type current by K+ may also be of physiological significance. |
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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.1995.sp020568 |