Modulation of single Ca2+-dependent K+-channel activity by protein phosphorylation

Abstract

There is considerable evidence that cyclic AMP can modulate the electrical activity of excitable cells and that protein phosphorylation by the catalytic subunit (CS) of cAMP-dependent protein kinase is a necessary step in these modulatory effects. In analogy to alterations in enzyme activities following phosphorylation, it seems possible that direct phosphorylation of ion-channel proteins may alter their gating properties, giving rise to the observe changes in electrical activity. However, the results obtained so far do not indicate whether it is ion channels themselves that are phosphorylated, or whether phosphorylation is simply an early step in some cascade of events which leads ultimately to modulation of channel activity. The development of single-channel recording techniques has provided a way to investigate this question. Here we describe effects of CS on the activity of individual CA2+-dependent K+ channels from the nervous system of the land snail Helix measured in isolated membrane patches and in artificial phospholipid bilayers. The results demonstrate that cAMP-dependent protein phosphorylation produces long-lasting changes in the activity of individual channels, and indicate that the relevant phosphorylation site is closely associated with the channel.

Purification of Ca2+‐activated K+ channel protein on calmodulin affinity columns after detergent solubilization of luminal membranes from outer renal medulla

“…The Ca2+-activated K+ channel can be solubilized by CHAPS and reconstituted into phospholipid vesicles with full preservation of its native properties [7]. In the reconstituted vesicles the K+ [8,10]. After demonstrating a high-affinity effect of calmodulin on the K+ channel, a method is developed for purification of the K+ channel protein on a calmodulin affinity column.…”

“…Ca2+ activation of the K+ channel from heart sarcolemma could not take place unless the Kf channel was in a phosphorylated state [lo]. Phosphorylation of the K+ channel from snail neurones [25] and snail helix ganglia [8] made the K+ channel more sensitive to Ca2+ but did not change the maximal K+ channel activity.…”

The 5‐HT4 receptor subtype inhibits K+ current in colliculi neurones via activation of a cyclic AMP‐dependent protein kinase

“…Phosphorylation/dephosphorylation of the channel itself or some modulatory intermediate events are the most common mechanisms (Rudy, 1988;Brown, 1990). Phosphorylation is the result of protein kinase C (PKC; Akerman et al, 1988;Doerner et al, 1988), adenosine 3':5'-cyclic monophosphate (cyclic AMP)-dependent protein kinase (PKA; Siegelbaum et al, 1982;Deterre et al, 1982;Ewald et al, 1985) or other Ca2"-activated protein kinase or phosphatase (Rudy, 1988;Hoger et al, 1991). Other mechanisms have been described, including direct interaction of Gi/Go proteins (Yatani et al, 1987;Von Dongen et al, 1988) or arachidonic acid metabolites (Piomelli et al, 1987).…”

Augmentation by external Mg ions of β‐adrenoceptor‐mediated actions in the longitudinal muscle of rat uterus

“…In the #-action, cyclic AMP may phosphorylate the K channels either directly or via cyclic AMP-dependent protein kinase as reported in Helix neurone (Ewald et al, 1985). Mg is considered to augment the activation of K channels by cyclic AMP through the process.…”