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1 Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA, USA; Department of Physiology and Pharmacology, Loma Linda University School of Medicine, Loma Linda, CA, USA
2 Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA, USA; Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA, USA
3 Department of Physiology and Pharmacology, Loma Linda University School of Medicine, Loma Linda, CA, USA
* To whom correspondence should be addressed. E-mail: llongo{at}som.llu.edu.
In ovine basilar arterial smooth muscle cells (SMCs), the fetal "big" calcium-activated potassium (BK) channel activity is significantly greater and has a lower Ca2+ set point than BK channels from adult cells. In the present study, we tested the hypothesis that these differences result from developmentally regulated phosphorylation of these channels. Using the patch clamp technique and a novel in situ enzymological approach, we measured the rates and extents of change of BK channel voltage-activation from SMC inside-out patch preparations in response to selective activation and inhibition of channel-associated protein phosphatases and kinases (CAPAKs). We show that BK channel activity is modulated during development by differential phosphorylation, and that the activities of CAPAKs change substantially during development. In particular, excised membrane patches from adult SMCs exhibited greater protein kinase A activity than those of the fetus. In contrast, SMCs of the fetus exhibited greater protein kinase G activity and phosphatase activity than those of the adult. These findings extend our previous observation that the BK channel calcium set point differs significantly in adult and fetal cerebrovascular myocytes, and suggest a biochemical mechanism for this difference. In addition, these findings suggest that the functional stoichiometry of the CAPAKs varies significantly during development, and that such variation may be a hitherto unrecognized mechanism of ion channel regulation.
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