Structure and function of resistance arteries from BB-creatine kinase and ubiquitous Mt-creatine kinase double knockout mice

Abstract

Increasing evidence indicates that the enzyme creatine kinase (CK) is intimately involved in microvascular contractility. The mitochondrial isoenzyme catalyses phosphocreatine synthesis from ATP, while cytoplasmic CK, predominantly the BB isoenzyme in vascular tissue, is tightly bound near myosin ATPase, where it favours ATP production from phosphocreatine to metabolically support vascular contractility. However, the effect of CK gene inactivation on microvascular function is hitherto unknown. We studied functional and structural parameters of mesenteric resistance arteries isolated from 5 adult male mice lacking cytoplasmic BB-CK and ubiquitous mitochondrial CK (CK-/-) vs 6 sex/age-matched controls. Using a Mulvany Halpern myograph, we assessed the acute maximum contractile force with 125 mM K⁺ and 10^-5 M norepinephrine, and the effect of two inhibitors, dinitrofluorobenzene, which inhibits phosphotransfer enzymes (0.1 μM), and the specific adenylate kinase inhibitor P1, P5-di(adenosine 5') pentaphosphate (10^-6 to 10^-5 M). WT and CK-/- did not significantly differ in media thickness, vascular elasticity parameters, or acute maximum contractile force. CK-/- arteries displayed greater reduction in contractility after dinitrofluorobenzene 38%; vs 14% in WT; and after AK inhibition, 14% vs 5.5% in WT, and displayed abnormal mitochondria, with a partial loss of the inner membrane. Thus, CK-/- mice display a surprisingly mild phenotype in vascular dysfunction. However, the mitochondrial abnormalities and greater effect of inhibitors on contractility may reflect a compromised energy metabolism. In CK-/- mice, compensatory mechanisms salvage energy metabolism, as described for other CK knock-out models.

Keywords: BB-creatine kinase isoenzyme; Creatine kinase; Knockout mice; Mitochondrial creatine kinase isoenzyme; Resistance arteries; Wire myograph.