K+-depolarization induces RhoA kinase translocation to caveolae and Ca2+-sensitization of arterial muscle

Nicole H. Urban, Krystina M. Berg, and Paul H. Ratz

Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia 23501

Abstract

KCl causes smooth muscle contraction by elevating intracellular free Ca²⁺, whereas receptor stimulation activates an additional mechanism, termed Ca²⁺-sensitization, that can involve activation of RhoA-associated kinase (ROK) and PKC. However, recent studies support the hypothesis that KCl may also increase Ca²⁺-sensitivity. Our data showed that the PKC inhibitor GF-109203X did not, whereas the ROK inhibitor Y-27632 did, inhibit KCl-induced tonic (5 min) force and myosin light chain (MLC) phosphorylation in rabbit artery. Y-27632 also inhibited BAY K 8644- and ionomycin-induced MLC phosphorylation and force but did not inhibit KClinduced Ca²⁺-entry or peak (_15 s) force. Moreover, KCl and BAY K 8644 nearly doubled the amount of ROK colocalized to caveolae at 30 s, a time that preceded inhibition of force by Y-27632. Colocalization was not inhibited by Y-27632 but was abolished by nifedipine and the calmodulin blocker trifluoperazine. These data support the hypothesis that KCl caused Ca²⁺-sensitization via ROK activation. We discuss a novel model for ROK activation involving translocation to caveolae that is dependent on Ca²⁺ entry and involves Ca²⁺-calmodulin activation.

Keywords: vascular smooth muscle; signal transduction; caveolin; Y-27632; confocal microscopy

Sumber : Am J Physiol Cell Physiol 285: C1377–C1385, 2003

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