M. Kubokawa et al., ROLE OF CA2+ CAMK-II IN CA2+-INDUCED K+ CHANNEL INHIBITION IN RAT CCDPRINCIPAL CELL/, American journal of physiology. Renal, fluid and electrolyte physiology, 37(2), 1995, pp. 211-219
The apical low-conductance K+ channel of rat cortical collecting duct
(CCD) is inhibited by increased intracellular Ca2+ concentrations. Thi
s effect has been shown to be mediated at least in part by activation
of protein kinase C (PKC). In the present study, we used the patch-cla
mp technique to examine the role of Ca2+/calmodulin-dependent protein
kinase II (CaMK II) in mediating the Ca2+-induced inhibitory effect. I
n cell-attached patches of principal cells of rat tubules, clamping of
intracellular Ca2+ concentration at 400 nM by using 1 mu M ionomycin
reduced channel activity to 26.5% of the control value. A further redu
ction in channel activity, to 8.8% of the control value, was observed
following the addition of phorbol 12-myristate 13-acetate (PMA), an ag
ent known to activate PKC. Pretreatment of cells with KN-62 (CaMK II i
nhibitor) or GF-109203X (PKC inhibitor) attenuated the inhibitory effe
ct of Ca2+ on K+ channel activity (83.2 and 50.7% of the control value
, respectively). Even in the presence of KN-62, addition of 10 mu M PM
A significantly decreased channel activity to 57.2% of the control val
ue. The Ca2+-induced inhibition was completely abolished by simultaneo
us incubation with both KN-62 and GF-109203X. In inside-out patches, a
ddition of 20 mu g/ml CaMK II in the presence of a PKC inhibitor reduc
ed channel activity to 66.2% of control values. It is concluded that C
aMK II is involved in mediating the Ca2+-induced inhibition of the act
ivity of the apical K+ channel of rat CCD.