Differential hyperpolarization to substance P and calcitonin gene-related peptide in smooth muscle versus endothelium of mouse mesenteric artery

Abstract

Objective: We sought to define how sensory neurotransmitters substance P and calcitonin gene-related peptide (CGRP) affect membrane potential of vascular smooth muscle and endothelium.

Methods: Microelectrodes recorded membrane potential of smooth muscle from pressurized mouse mesenteric arteries (diameter, ~150 µm) and in endothelial tubes.

Results: Resting potential was similar (~ -45 mV) for each cell layer. Substance P hyperpolarized smooth muscle and endothelium ~ -15 mV; smooth muscle hyperpolarization was abolished by endothelial disruption or NO synthase inhibition. Blocking K_Ca channels (apamin + charybdotoxin) attenuated hyperpolarization in both cell types. CGRP hyperpolarized endothelium and smooth muscle ~ -30 mV; smooth muscle hyperpolarization was independent of endothelium. Blocking K_Ca channels prevented hyperpolarization to CGRP in endothelium but not smooth muscle. Inhibiting K_ATP channels with glibenclamide or genetic deletion of K_IR 6.1 attenuated hyperpolarization in smooth muscle but not endothelium. Pinacidil (K_ATP channel agonist) hyperpolarized smooth muscle more than endothelium (~ -35 vs. ~ -20 mV).

Conclusions: Calcitonin gene-related peptide elicits greater hyperpolarization than substance P. Substance P hyperpolarizes both cell layers through K_Ca channels and involves endothelium-derived NO in smooth muscle. Endothelial hyperpolarization to CGRP requires K_Ca channels, while K_ATP channels mediate hyperpolarization in smooth muscle. Differential K⁺ channel activation in smooth muscle and endothelium through sensory neurotransmission may selectively tune mesenteric blood flow.

Keywords: membrane potential; neurotransmitters; nitric oxide; sensory nerves.