Regulation of Ca2+-activated K+ channels by multifunctional Ca2+/calmodulin-dependent protein kinase

Activation of mesangial cells by ANG II provokes release of intracellular C a2+ stores and subsequent Ca2+ influx through voltage-gated channels, event s that are reflected by a large transient increase in intracellular concent ration [Ca2+](i) followed by a modest sustained elevation in [Ca2+](i). The se ANG II-induced alterations in [Ca2+](i) elicit activation of large Ca2+- activated K+ channels (BKCa) in a negative-feedback manner. The mechanism o f this BKCa feedback response may involve the direct effect of intracellula r Ca2+ on the channel and/or channel activation by regulatory enzymes. The present study utilized patch-clamp and fura 2 fluorescence techniques to as sess the involvement of multifunctional calcium calmodulin kinase II (CAMKI I) in the BKCa feedback response. In cell-attached patches, KN62 (specific inhibitor of CAMKII) either abolished or reduced to near zero the ANG II-in duced BKCa feedback response. This phenomenon did not reflect direct effect s of KN62 on the BKCa channel, because this agent alone did not significant ly alter BKCa channel activity in inside-out patches. KN62 also failed to a lter either the transient peak or sustained plateau phases of the [Ca2+](i) response to ANG II. In inside-out patches (1 mu M Ca2+ in bath), calmoduli n plus ATP activated BKCa channels in the presence but not the absence of C AMKII. These observations are consistent with the postulate that CAMKII is involved in the BKCa feedback response of mesangial cells, acting to potent iate the influence of increased [Ca2+](i) on the BKCa channel or a closely associated regulator of the channel. An additional effect of CAMKII to acti vate a voltage-gated Ca2+ channel cannot be ruled out by these experiments.