Functional Bias of Contractile Control in Mouse Resistance Arteries

Background

Constrictor agonists set vascular tone through two coupling processes, one tied to (electromechanical), the other independent (pharmacomechanical) of membrane potential (V _M ). This arrangement raises an intriguing query: are they variably recruited such that each agonist elicits a range of vasomotor signatures, functionally biased towards one mechanism or the other? This query underlies this study and our examination of agonist-induced arterial constriction.

Methods

Mouse mesenteric arteries were exposed to a classic G _q/11 (phenylephrine) or G _q/11 /G _12/13 (U46619) coupled receptor agonist, and responses monitored in the absence and presence of L-type Ca ²⁺ channel/protein kinase inhibitors. Contractile work was supplemented with measures of protein phosphorylation, V _M , and cytosolic Ca ²⁺ ; conceptual insights were enhanced with computational modeling.

Results

Each constrictor elicited a response curve that was attenuated and rightward shifted by nifedipine, findings aligned with functional bias; electromechanical coupling preceded pharmacomechanical, the latter’s importance rising with agonist concentration. Ensuing contractile and phosphorylation (CPI-17 & MYPT1 (T-855 & T-697)) measures revealed phenylephrine-induced pharmacomechanical coupling was tied to protein kinase C (PKC), while U46619 was tied to both PKC and Rho-kinase. A switch to pharmacomechanical coupling dominance occurred when agonist superfusion was replaced with discrete application to a small portion of artery. This switch was predicted by electromechanical modeling and supported by direct measures of V _M and cytosolic Ca ²⁺ .

Conclusions

Our work illustrates that constrictor agonists elicit functionally biased responses and that arteries toggle among contractile mechanisms, dependent on receptor signal bias, structural/electrical properties, and how agents are applied. We discuss how hemodynamic control is intimately tied to functional bias in both health and disease states, including but not limited to arterial vasospasm.

Highlights

• Agonist-induced constrictor responses exhibit a “functional bias” toward electromechanical or pharmacomechanical coupling dependent on agent concentration and mode of application.

• Electromechanical coupling typically but not exclusively precedes pharmacomechanical, the latter rising to prominence with agent concentration. Pharmacomechanical coupling is mediated through receptor pathways linked to PKC and Rho-kinase, regulatory proteins that target the catalytic and targeting subunit of MLCP.

• Functional bias is malleable and thus each agonist elicits a range of vasomotor signatures, each presumptively important in controlling blood flow delivery in space and time.