Ionizing radiation alters myofilament calcium sensitivity in vascular smooth muscle: potential role of protein kinase C

Abstract

Radiation exposure increases vascular responsiveness, and this change involves endothelial damage, as well as direct effects on vascular smooth muscle. In this study, we tested the hypothesis that myofilament Ca(2+) sensitivity in vascular smooth muscle is increased from single whole body gamma irradiation (6 Gy). We measured contractile responses from intact and permeabilized rat thoracic aortic rings combined with cytosolic Ca(2+) ([Ca(2+)](i)) measurements. The sensitivity to KCl and phenylephrine increased significantly in tissues from animals on the 9th and 30th days postirradiation compared with control. Irradiation also significantly increased Ca(2+) sensitivity in beta-escin permeabilized smooth muscle on the 9th and 30th days postirradiation. Inhibitors of protein kinase C, chelerythrine, and staurosporine, had no effect on the pCa-tension curves in control permeabilized tissues but significantly decreased Ca(2+) sensitivity in permeabilized tissues on the 9th and 30th days postirradiation. Phorbol dibutyrate (PDBu, 10(-7) M) increased Ca(2+) sensitivity in control skinned smooth muscle but was without effect in irradiated vascular rings. Simultaneous measurement of contractile force and [Ca(2+)](i) showed that myofilament Ca(2+) sensitivity defined as the ratio of force change to [Ca(2+)](i) significantly increased following gamma-irradiation. PDBu (10(-6) M) stimulation of intact aorta produced a sustained contraction, while the increase in [Ca(2+)](i) was transient. In irradiated tissues, PDBu-induced contractions were greater than those seen in control tissues but there was no elevation in [Ca(2+)](i). Taken together, these data strongly support the hypothesis that irradiation increases the sensitivity of vascular smooth muscle myofilaments to Ca(2+) and this effect is dependent on activation of protein kinase C.

Electrophysiological and contractile evidence of the ability of human mesenchymal stromal cells to correct vascular malfunction in rats after ionizing irradiation

“…Our experiments demonstrated that myofilament Ca 2? sensitivity is increased 9 days after irradiation, the earliest time point measured, and persisted over the 30 day experimental period [15].…”

“…channel (BK Ca ) activity in endothelial cells [2]. Nevertheless, although endothelium is the most radiation-sensitive and vulnerable component of the vascular wall, the studies performed have shown that irradiation has the ability to enhance vascular contractility in an endothelium-independent manner [3,15]. Another potential mechanism by which vascular tone could be enhanced is through changes in the transmembrane potential of the vascular SMC or myofilament calcium sensitivity.…”

Rho kinase and protein kinase C involvement in vascular smooth muscle myofilament calcium sensitization in arteries from diabetic rats

“…In the vasculature, PKC and ROCK are the two key regulatory enzymes involved in the signal transduction of multiple cellular functions such as growth, Rho kinase and PKC in diabetic arterial contractility IV Kizub et al differentiation, metabolism and smooth muscle contractility (Amano et al, 2000;Meier and King, 2000;Wettschureck and Offermanns, 2002;Seko et al, 2003;Stanton et al, 2004;Ward et al, 2004;Soloviev et al, 2005;Loirand et al, 2006). In particular, ROCK-and PKC-dependent sensitization of the contractile apparatus to Ca 2+ have been suggested to play an important role in the signal transduction events leading to VSM contraction and, incidentally, in the development of hypertensive conditions (Fu et al, 1998;Soloviev et al, 1998;Meier and King, 2000;De Witt et al, 2001;Janssen et al, 2001;Ward et al, 2004;Salamanca and Khalil, 2005).…”

“…Vessels were placed into relaxing solution of the following composition (in mM): Na 2ATP 3.3; KCl 130, MgCl2 2.5, Tris 20, imidasole 20, EGTA 4, phosphocreatine 12; creatine phosphokinase 15 u·mL -1 ; pH 6.7 at 21°C. After equilibration in this solution for 30 min, the tissue was permeabilized (skinned) using a mix of cholesterolprecipitated compounds, saponin (0.05%) and b-escin (60 mM) in relaxing solution for 18 min at room temperature (Soloviev et al, 2005). As receptor agonists were not used, no Rho kinase and PKC in diabetic arterial contractility IV Kizub et al GTP was added to this solution (e.g.…”

α- and ϵ-Protein Kinase C Activity during Smooth Muscle Cell Apoptosis in Response to γ-Radiation

“…These observations can be partly explained by the possibility that 10 Gy ␥-radiation may cause Ca 2ϩ sensitization of the contractile myofilament to Achstimulated Ca 2ϩ influx. This is supported by studies in vascular smooth muscle that demonstrated that 6 Gy ionizing radiation alters myofilament Ca 2ϩ sensitivity and contraction through a potential role of PKC (Soloviev et al, 2005). The Ca 2ϩ sensitization mechanism was not evident in GPISMLL strips exposed to 30 and 50 Gy; instead, a significant decrease in contraction was observed (Fig.…”