ISSN:
1432-1424
Keywords:
Ca2+ channel
;
Characeae
;
membrane excitation
;
Nitellopsis
;
phosphoprotein phosphatase
;
protein phosphorylation
;
tonoplast-free cell
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary The regulation of voltage-dependent Ca2+ channels by protein phosphorylation and dephosphorylation was studied using tonoplast-free cells ofNitellopsis. Since the Ca2+-channel activation has a dominant role in the membrane excitation of tonoplast-free cells (T. Shiina and M. Tazawa,J. Membrane Biol. 96:263–276, 1987), it seems to be reasonable to assume that any change of the membrane excitability reflects a modulation of the Ca2+ channel. When agents that enhance phosphoprotein dephosphorylation (protein kinase, inhibitor, phosphoprotein phosphatase-1, -2A) were introduced to the intracellular surface of the plasmalemma (twice-perfused tonoplast-free cells), the membrane potential depolarized and the membrane resistance decreased under current-clamp experiments. By contrast, when cells were challenged with agents that enhance protein phosphorylation (phosphoprotein phosphatase inhibitor-1, α-naphthylphosphate), the membrane potential hyperpolarized, and the membrane resistance increased. When phosphoprotein phosphatase-1 or -2A was perfused, the current-voltage (I–V) curve which was obtained under ramp voltage-clamp condition exhibited the so-called N-shaped characteristic, indicating an acceleration of the Ca2+-channel activation. This effect was suppressed by the addition of phosphoprotein phosphatase inhibitors. ATP-γ-S, which is assumed to stimulate protein phosphorylation, decreased the inward current in theI–V curve. The dependence of the Ca2+-channel activation on intracellular ATP was different between the once-perfused and twice-perfused cells. In once-perfused cells, the membrane excitability was reduced by low intracellular ATP concentration. By contrast, in twice-perfused cells, excitability was enhanced by ATP.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01925719
Permalink
