Glucose-Dependent Enhancement of Spontaneous Phasic Contraction Is Suppressed in Diabetic Mouse Portal Vein: Association with Diacylglycerol-Protein Kinase C Pathway

The ischemic metabolite lysophosphatidylcholine increases rat coronary arterial tone by endothelium-dependent mechanisms

Lysophosphatidylcholine (LPC), a hydrolysis product of phospholipid degradation, accumulates in the ischemic myocardium. Using isolated hearts or rat coronary septal arteries, we tested the impact of LPC in modulating basal function or the responses to vasoactive agents. Sustained perfusion of hearts with LPC augmented coronary perfusion pressure (CPP) and reduced left ventricular developed pressure (LVDP). By mechanisms that have yet to be identified, these effects on CPP and LVDP were exaggerated when LPC was removed from the perfusate. Although LPC (or its washout) had no direct effect on vascular tone in the isolated coronary artery, it selectively potentiated the receptor-coupled vasoconstrictor response to U-46619, a thromboxane A(2) mimetic. Interestingly, when LPC was washed out, the potentiation to U-46619 was even more pronounced. Both the immediate and residual effects of LPC were endothelium-dependent. EDHF was likely the sole mediator responsible for the direct effects of LPC on U-46619-vasoconstriction, whereas the augmented vasoconstrictor responses following LPC washout may in part be related to an increase in ET-1, and a striking reduction in the bioavailability of NO. Our data suggest that in addition to reducing the accumulation of LPC to prevent ischemia-reperfusion (I/R) damage, efforts targeting an improved endothelium-dependent regulation of vascular tone could be an attractive approach to limit the cardiac damage induced by I/R.

Glucose-dependent enhancement of diabetic bladder contraction is associated with a rho kinase-regulated protein kinase C pathway

Urinary bladder dysfunction, which is one of the most common diabetic complications, is associated with alteration of bladder smooth muscle contraction. However, details regarding the responses under high-glucose (HG) conditions in diabetes are poorly understood. The objective of this study was to identify a relationship between extracellular glucose level and bladder smooth muscle contraction in diabetes. Bladder smooth muscle tissues were isolated from spontaneously type II diabetic (ob/ob mouse; 16-20 weeks of age, male) and age-matched control (C57BL mouse) mice. Carbachol (CCh) induced time- and dose-dependent contractions in ob/ob and C57BL mice; however, maximal responses differed significantly (14.34 +/- 0.32 and 12.69 +/- 0.22 mN/mm(2) after 30 microM CCh treatment, respectively; n = 5-8). Pretreatment of bladders under HG conditions (22.2 mM glucose; concentration is twice that of normal glucose for 30 min) led to enhancement of CCh-induced contraction solely in diabetic mice (15.9 +/- 0.26 mN/mm(2); n = 5). Basal extracellular glucose-dependent enhancement of bladder contraction in diabetes was documented initially in this study. The correlation between intracellular calcium concentration and contraction was enhanced only in the ob/ob mouse. This enhancement of contraction and total protein kinase C (PKC) activity were inhibited by pretreatment with not only a PKC inhibitor (rottlerin) but also with a rho kinase inhibitor, fasudil [1-(5-isoquinolinesulfonyl)homopiperazine HCl]. These reagents also suppressed the differences between ob/ob and C57BL mouse bladder contractions under HG conditions. The data indicated that glucose-dependent enhancement of contraction in diabetic bladder is involved in the activation of the rho kinase and calcium-independent PKC pathways. This dysfunction may contribute to bladder complications such as detrusor overactivity and reduced bladder capacity in diabetes.

Intra- and extrarenal arteries exhibit different profiles of contractile responses in high glucose conditions

BACKGROUND AND PURPOSE

The renal artery (RA) has been extensively investigated for the assessment of renal vascular function/dysfunction; however, few studies have focused on the intrarenal vasculature.

EXPERIMENTAL APPROACH

We devised a microvascular force measurement system, which allowed us to measure contractions of interlobar arteries (ILA), isolated from within the mouse kidney and prepared without endothelium.

KEY RESULTS

KCl (50 mM) induced similar force development in the aorta and RA but responses in the ILA were about 50% lower. Treatment of RA with 10 microM phenylephrine (PE), 10 nM U46619 (thromboxane A(2) analogue) or 10 microM prostaglandin F(2 alpha) elicited a response greater than 150% of that induced by KCl. In ILA, 10 nM U46619 elicited a response that was 130% of the KCl-induced response; however, other agonists induced levels similar to that induced by KCl. High glucose conditions (22.2 mM glucose) significantly enhanced responses in RA and ILA to PE or U46619 stimulation. This enhancement was suppressed by rottlerin, a calcium-independent PKC inhibitor, indicating that glucose-dependent, enhanced small vessel contractility in the kidney was linked to the activation of calcium-independent PKC.

CONCLUSION AND IMPLICATIONS

Extra- and intrarenal arteries exhibit different profiles of agonist-induced contractions. In ILA, only U46619 enhanced small vessel contractility in the kidney, which might lead to renal dysfunction and nephropathy through reduced intrarenal blood flow rate. A model has been established, which will allow the assessment of contractile responses of intrarenal arteries from murine models of renal disease, including type 2 diabetes.

High-Glucose-Altered Endothelial Cell Function Involves Both Disruption of Cell-to-Cell Connection and Enhancement of Force Development

Vascular endothelial cells (ECs), which regulate vascular tonus, serve as a barrier at the interface of vascular tissue. It is generally believed that alteration of this barrier is correlated with diabetic complications; however, a detailed mechanism has not been elucidated. This study examined alteration of bovine arterial EC functions stimulated by a thromboxane A2 analog (9,11-dideoxy-11 alpha,9 alpha-epoxymethano prostaglandin F(2 alpha); U46619) under normal and high-glucose (HG) conditions. U46619 treatment increased EC layer permeability in a time- and dose-dependent fashion. This response initially disrupted calcium-dependent EC-to-EC connections, namely, vascular endothelial cadherin (VE-CaD). Thereafter, EC force development in association with morphological changes was detected employing a reconstituted EC fiber technique, resulting in paracellular hole formation in the EC layer. Thus, we confirmed that U46619-induced enhancement of EC layer permeability involves these sequential steps. Similar trials were performed using a concentration twice that of normal glucose (22.2 mM glucose for 48 h). This treatment significantly enhanced U46619-induced EC layer permeability; furthermore, increases in both rate of VE-CaD disruption and EC fiber contraction were evident. Inhibition of calcium-independent protein kinase C and diacylglycerol kinase indicated that the glucose-dependent increase in VE-CaD disruption was mediated by a calcium-independent mechanism. Moreover, EC contraction was regulated by a typical calcium-independent pathway associated with rho kinase and actin stress fiber. Contraction was also enhanced under HG conditions. This investigation revealed that glucose-dependent enhancement of EC layer permeability is related to increases in VE-CaD disruption and EC contraction. Increases in both parameters were mediated by alteration of a calcium-independent pathway.

Regulation of the spontaneous contractile activity of the portal vein by the sarcoplasmic reticulum: evidence from the phospholamban gene-ablated mouse

The rapid contraction/relaxation cycles of phasic smooth muscles necessitates intracellular calcium cycling at a more rapid rate than that of tonic smooth muscles. Recent studies suggest that sarcoplasmic reticulum calcium handling is an important determinant of portal vein phasic contractions. We evaluated the importance and role of phospholamban, a protein which inhibits the sarcoplasmic reticulum (SR) calcium ATPase (SERCA), in regulating the contractility of the phasic mouse portal vein. PLB gene ablation significantly reduced the basal frequency of spontaneous mechanical activity and increased force development of the portal vein. Cyclopiazonic acid (CPA), an inhibitor of SERCA, did not significantly affect the spontaneous activity of the wild-type (WT) portal vein. CPA (1 microM) eliminated the differences in frequency and force between the PLB-KO and WT, localizing the effects to the SR. The PLB-KO portal vein had a lower resting membrane potential than WT controls. There were no significant differences between WT and KO responses to charybdotoxin (250 nM), indicating that calcium-activated potassium channels do not contribute to altered KO portal vein contractility. While contractile sensitivity to acetylcholine was not different between WT and PLB-KO portal veins, force generated in response to a given concentration of acetylcholine was significantly greater in the PLB-KO portal vein, both in the absence and presence of CPA. Our results confirm that SR activity can play a major role in modulating the frequency of the spontaneous mechanical activity of portal veins and removal of PLB inhibition of the SR calcium ATPase has significant effects on the spontaneous activity of the portal vein.