ISSN:
1432-1424
Keywords:
Ca2+-activated K+ current
;
Ca2+ channel
;
Zea mays
;
1,4-dihydropyridine
;
phenylalkylamine
;
patch clamp
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary The voltage- and time-dependent K+ current,I K + out , elicited by depolarization of corn protoplasts, was inhibited by the addition of calcium channel antagonists (nitrendipine, nifedipine, verapamil, methoxyverapamil, bepridil, but not La3+) to the extracellular medium. These results suggested that the influx of external Ca2+ was necessary for K+ current activation. The IC50, concentration of inhibitor that caused 50% reduction of the current, for nitrendipine was 1 μm at a test potential of +60 mV following a 20-min incubation period. In order to test whether intracellular Ca2+ actuated the K+ current, we altered either the Ca2+ buffering capacity or the free Ca2+ concentration of the intracellular medium (pipette filling solution). By these means,I K + out could be varied over a 10-fold range. Increasing the free Ca2+ concentration from 40 to 400nm also shifted the activation of the K+ current toward more negative potentials. Maintaining cytoplasmic Ca2+ at 500nm with 40nm EGTA resulted in a more rapid activation of the K+ current. Thus the normal rate of activation of this current may reflect changes in cytoplasmic Ca2+ on depolarization. Increasing intracellular Ca2+ to 500nm or 1 μm also led to inactivation of the K+ current within a few minutes. It is concluded thatI K + out is regulated by cytosolic Ca2+, which is in turn controlled by Ca2+ influx through dihydropyridine-, and phenylalkylamine-sensitive channels.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01868732
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