Abstract
Objective- Inward rectifying K+ (KIR) channels are present in cerebral arterial smooth muscle and endothelial cells, a tandem arrangement suggestive of a dynamic yet undiscovered role for this channel. This study defined whether distinct pools of cerebral arterial KIR channels were uniquely modulated by membrane lipids and hemodynamic stimuli. Approach and Results- A Ba2+-sensitive KIR current was isolated in smooth muscle and endothelial cells of rat cerebral arteries; molecular analyses subsequently confirmed KIR2.1/KIR2.2 mRNA and protein expression in both cells. Patch-clamp electrophysiology next demonstrated that each population of KIR channels was sensitive to key membrane lipids and hemodynamic stimuli. In this regard, endothelial KIR was sensitive to phosphatidylinositol 4,5-bisphosphate content, with depletion impairing the ability of laminar shear stress to activate this channel pool. In contrast, smooth muscle KIR was sensitive to membrane cholesterol content, with sequestration blocking the ability of pressure to inhibit channel activity. The idea that membrane lipids help confer shear stress and pressure sensitivity of KIR channels was confirmed in intact arteries using myography. Virtual models integrating structural/electrical observations reconceptualized KIR as a dynamic regulator of membrane potential working in concert with other currents to set basal tone across a range of shear stresses and intravascular pressures. Conclusions- The data show for the first time that specific membrane lipid-KIR interactions enable unique channel populations to sense hemodynamic stimuli and drive vasomotor responses to set basal perfusion in the cerebral circulation.
Highlights
Approach and Results—A Ba2+-sensitive KIR current was isolated in smooth muscle and endothelial cells of rat cerebral arteries; molecular analyses subsequently confirmed KIR2.1/KIR2.2 mRNA and protein expression in both cells
KIR Channel Expression in Cerebral Vascular Cells This examination began with a characterization of KIR2.x expression in cerebral arterial smooth muscle and endothelium
Optimal neural activity relies on balanced blood flow delivery, a process intimately linked to VM and the maintenance of cerebral vascular tone
Summary
Smooth muscle cells (SMCs) were enzymatically isolated as previously described.[27] Briefly, arterial segments were placed in an isolation medium (37°C, 10 minutes) containing (in mmol/L): 60 NaCl, 80 Na-glutamate, 5 KCl, 2 MgCl2, 10 glucose, and 10 HEPES with 1 mg/ mL bovine serum albumin (BSA; pH 7.4). Conventional patch-clamp electrophysiology was used to measure whole-cell currents in both isolated smooth muscle and ECs. Briefly, recording electrodes (resistance of 5–8 MΩ when filled with solution) were pulled from borosilicate glass microcapillary tubes (Sutter Instruments, Novato, CA), covered in dental wax to reduce capacitance, and backfilled with pipette solution containing (in mmol/L): 5 NaCl, 35 KCl, 100 K-gluconate, 1 CaCl2, 0.5 MgCl2, 10 HEPES, 10 EGTA, 2.5 Na2-ATP, and 0.2 GTP (pH 7.2). To estimate Km, a constant determining the dynamic range of excitation-contraction coupling, a minimal diameter, D , was added min to the sigmoid and this function was fitted to the observed relationship between simultaneously measured VM and outer vessel diameter in cerebral vessels (Figure I in the online-only Data Supplement)[6] from the fit, Km=0.134
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
