ISSN:
1432-1424
Keywords:
Key words: Maxi K+ channel — Calcium — Phosphorylation — Dephosphorylation — cAMP dependent protein kinase — Rabbit distal colon
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract. The Ca2+-activated maxi K+ channel is predominant in the basolateral membrane of the surface cells in the distal colon. It may play a role in the regulation of the aldosterone-stimulated Na+ reabsorption from the intestinal lumen. Previous measurements of these basolateral K+ channels in planar lipid bilayers and in plasma membrane vesicles have shown a very high sensitivity to Ca2+ with a K 0.5 ranging from 20 nm to 300 nm, whereas other studies have a much lower sensitivity to Ca2+. To investigate whether this difference could be due to modulation by second messenger systems, the effect of phosphorylation and dephosphorylation was examined. After addition of phosphatase, the K+ channels lost their high sensitivity to Ca2+, yet they could still be activated by high concentrations of Ca2+ (10 μm). Furthermore, the high sensitivity to Ca2+ could be restored after phosphorylation catalyzed by a cAMP dependent protein kinase. There was no effect of addition of protein kinase C. In agreement with the involvement of enzymatic processes, lag periods of 30–120 sec for dephosphorylation and of 10–280 sec for phosphorylation were observed. The phosphorylation state of the channel did not influence the single channel conductance. The results demonstrate that the high sensitivity to Ca2+ of the maxi K+ channel from rabbit distal colon is a property of the phosphorylated form of the channel protein, and that the difference in Ca2+ sensitivity between the dephosphorylated and phosphorylated forms of the channel protein is more than one order of magnitude. The variety in Ca2+ sensitivities for maxi K+ channels from tissue to tissue and from different studies on the same tissue could be due to modification by second messenger systems.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s002329900053
Permalink
