ISSN:
1432-1424
Keywords:
Ca2+
;
decamethonium
;
quinine
;
charybdotoxin
;
tetracaine
;
4-aminopyridine
;
apamin
;
dendrotoxin
;
pinacidil
;
inositol
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary The outer membranes of plant cells contain channels which are highly selective for K+. However, many of their properties and their similarities to K+ channels found in animal cells had not previously been established. The channels open when the cells are depolarized in solutions with a high K+/Ca2+ ratio. In this work, the pharmacology of a previously identified plant K+ channel was examined. This survey showed that the channels have many properties which are similar to those of high-conductance Ca2+-activated K+ channels (highG K+(Ca2+)). K+ currents inChara were reduced by TEA+, Na+, Cs+, Ba2+, decamethonium and quinine, all inhibitors of, among other things, highG K+(Ca2+) channels. Tetracaine also inhibited K+ currentsChara, but its effect on most types of K+ channels in animal tissues is unknown. The currents were not inhibited by 4-aminopyridine (4AP), caffeine, tolbutamide, dendrotoxin, apamin or tubocurarine, which do not inhibit highG K+(Ca2+) channels, but affect other classes of K+ channels. The channels were “locked open” by 4AP, in a remarkably similar manner to that reported for K+(Ca2+) channels of a molluscan neuron. No evidence for the role of the inositol cycle in channel behavior was found, but its role in K+ channel control in animal cells is obscure. Potassium conductance was slightly decreased upon reduction of cytoplasmic ATP levels by cyanide + salicylhydroxamic acid (SHAM), consistent with channel control by phosphorylation. The anomalously strong voltage dependence of blockade by some ions (e.g. Cs+) is consistent with the channels being multiion pores. However, the channels also demonstrate some differences from the highG K+(Ca2+) channels found in animal tissues. The venom of the scorption,Leiurus quinquestriatus (LQV), and a protein component, charybdotoxin (CTX), an apparently specific inhibitor of highG K+(Ca2+) channels in various animal tissues, had no effect on the K+ channels in theChara plasmalemma. Als,, pinacidil, an antihypertensive drug which may increase highG K+(Ca2+) channel activity had no effect on the channels inChara. Although the described properties of theChara K+ channels are most similar to those of high conductance K+(Ca2+) in animal cells, the effects of CTX and pinacidil are notably different; the channels are clearly of a different structure to those found in animal cells, but are possibly related.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01870946
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