Lorenz, J.Riddervold, M.Spencer, E.Baker, S.Perrino, B.2008-08-122008-08-122002American Journal of Physiology - Cell Physiology, 2002; 283(5):C1399-C14130363-61431522-1563http://hdl.handle.net/2440/47321Ca²⁺/calmodulin-dependent protein kinase II (CaM kinase II) is regulated by calcium oscillations, autophosphorylation, and its subunit composition. All four subunit isoforms were detected in gastric fundus and proximal colon smooth muscles by RT-PCR, but only the and isoforms are expressed in myocytes. Relative and message levels were quantitated by real time PCR. CaM kinase II protein and Ca2+/calmodulin-stimulated (total) activity levels are higher in proximal colon smooth muscle lysates than in fundus lysates, but Ca²⁺/calmodulin-independent (autonomous) activity is higher in fundus lysates. CaM kinase II in fundus lysates is relatively unresponsive to Ca²⁺/calmodulin. Alkaline phosphatase decreased CaM kinase II autonomous activity in fundus lysates and restored its responsiveness to Ca²⁺/calmodulin. Acetylcholine (ACh) increased autonomous CaM kinase II activity in fundus and proximal colon smooth muscles in a time- and dose-dependent manner. KN-93 enhanced ACh-induced fundus contractions but inhibited proximal colon contractions. The different properties of CaM kinase II from fundus and proximal colon smooth muscles suggest differential regulation of its autophosphorylation and activity in tonic and phasic gastrointestinal smooth muscles.enCopyright © 2002 by the American Physiological Society.calmodulinprotein kinasephosphorylationtonic smooth musclephasic smooth muscleJournal article00200821392008081215090210.1152/ajpcell.00020.20020001784665000082-s2.0-003683781942334