Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB376

Poster Communications

Disruption of the smooth muscle actin cytoskeleton decreases human resistance artery stiffness and abolishes smooth muscle contractile function

M. Bloksgaard1, M. Morales-Quinones2, L. Martinez-Lemus2

1. Institute of Molecular Medicine - Department of Cardiovascular and Renal Research, University of Southern Denmark, Odense C, Denmark. 2. Dalton Cardiovascular Research Center, University of Missouri - Columbia, Columbia, Missouri, United States.

Resistance arteries (RA) are remodeled in hypertension, diabetes and obesity. We hypothesized that actin cytoskeleton polymerization, and thereby wall stiffness, is increased in resistance arteries from hypertensive human individuals compared to normotensive controls. RA were isolated from human omental fat obtained from either bariatric or other abdominal surgeries at The University of Missouri Hospital after patients were informed and written consent secured. Collection and use of human specimens were approved by IRB #2003033 and all procedures adhere to the guidelines in the World Medical Association's Declaration of Helsinki. Resistance artery segments (n = 58 patients, 37 females (11 / 26 non-bariatrics /bariatrics), 18 males (7 / 11 non-bariatrics / bariatrics), 3 unknown (excluded form analyses)) were isolated, subjected to pressurization from 5 to 120 mmHg and depressurization to 5 mmHg under passive conditions (calcium-free buffer with 100 µM adenosine and 2 mM EGTA) before and after 1 hour incubation with 2 µM mycalolide B at 5 mmHg to disrupt the actin cytoskeleton. Internal diameter and left and right wall thicknesses were recorded continuously. Smooth muscle cell contractile ability was assessed at 40 mmHg as a decrease in internal diameter (constriction) after exposure to 80 mM K+ at the beginning and end of the experimental protocol. The effect of mycalolide B, K+ and the influence of surgery type hereon was evaluated by two-tailed, paired t-test and two-way, repeated measurement ANOVA, respectively. The level of significance was pre-set to 0.05. Mean diameter, wall thickness and wall-to-lumen ratio at 100 mmHg were 366 ± 158 µm, 28 ± 10 µm and 16.6 ± 0.06 %, respectively. Mycalolide B did not affect the passive, internal diameter at 100 mmHg, but increased wall thickness slightly, yet significantly (3.5 ± 6 µm, p < 0.0001). As expected, mycalolide B completely abolished smooth muscle contractile function (constriction in % upon K+ exposure was 27 ± 20 and 0.4 ± 5, before and after mycalolide B treatment, respectively). Stress-strain relationships were calculated and the Young's elastic modulus, Einc, determined as described (1). Einc was decreased significantly by Mycalolide B treatment (9 ± 21 kPa, p = 0.0016) and the ability of the RA wall to absorb energy (calculated as described (2)) decreased significantly (10 ± 16 %, p < 0.0001). There were no differences between RA from bariatric patients versus non bariatrics. We conclude that the smooth muscle cytoskeleton has a small, but highly significant impact on the passive RA mechanics contributing to vascular wall stiffness and as expected, is essential for smooth muscle contractile function. Inclusion of additional patient demographic and clinical data and further analyses are required to confirm or reject the hypothesis.

Where applicable, experiments conform with Society ethical requirements