Objective—: Intercellular conduction of electrical signals underlies spreading vasodilation of resistance arteries. Small- and intermediate-conductance Ca ²⁺ -activated K ⁺ channels of endothelial cells serve a dual function by initiating hyperpolarization and modulating electrical conduction. We tested the hypothesis that regulation of electrical signaling by small- and intermediate-conductance Ca ²⁺ -activated K ⁺ channels is altered with advancing age. Approach and Results—: Intact endothelial tubes (60 µm wide; 1–3 mm long) were freshly isolated from male C57BL/6 mouse (Young: 4–6 months; Intermediate: 12–14 months; Old: 24–26 months) superior epigastric arteries. Using dual intracellular microelectrodes, current was injected (±0.1–3 nA) at site 1 while recording membrane potential ( V _m ) at site 2 (separation distance: 50–2000 µm). Across age groups, greatest differences were observed between Young and Old. Resting V _m in Old (−38±1 mV) was more negative ( P <0.05) than Young (−30±1 mV). Maximal hyperpolarization to both direct (NS309) and indirect (acetylcholine) activation of small- and intermediate-conductance Ca ²⁺ -activated K ⁺ channels was sustained (Δ V _m ≈−40 mV) with age. The length constant (λ) for electrical conduction was reduced ( P <0.05) from 1630±80 µm (Young) to 1320±80 µm (Old). Inhibiting small- and intermediate-conductance Ca ²⁺ -activated K ⁺ channels with apamin+charybdotoxin or scavenging hydrogen peroxide (H ₂ O ₂ ) with catalase improved electrical conduction ( P <0.05) in Old. Exogenous H ₂ O ₂ (200 µmol/L) in Young evoked hyperpolarization and impaired electrical conduction; these effects were blocked by apamin+charybdotoxin. Conclusions—: Enhanced current loss through Ca2+-activated K+ channel activation impairs electrical conduction along the endothelium of resistance arteries with aging. Attenuating the spatial domain of electrical signaling will restrict the spread of vasodilation and thereby contribute to blood flow limitations associated with advanced age.

Rationale:: Electrical conduction through gap junction channels between endothelial cells of resistance vessels is integral to blood flow control. Small and intermediate-conductance Ca ²⁺ -activated K ⁺ channels (SK _Ca /IK _Ca ) initiate electrical signals in endothelial cells, but it is unknown whether SK _Ca /IK _Ca activation alters signal transmission along the endothelium. Objective:: We tested the hypothesis that SK _Ca /IK _Ca activity regulates electrical conduction along the endothelium of resistance vessels. Methods and Results:: Freshly isolated endothelial cell tubes (60 μm wide; 1–3 mm long; cell length, ≈35 μm) from mouse skeletal muscle feed (superior epigastric) arteries were studied using dual intracellular microelectrodes. Current was injected (±0.1–3 nA) at site 1 while recording membrane potential (V _m ) at site 2 (separation distance=50–2000 μm). SK _Ca /IK _Ca activation (NS309, 1 μmol/L) reduced the change in V _m along endothelial cell tubes by ≥50% and shortened the electrical length constant (λ) from 1380 to 850 μm ( P 30 mV) was prevented with 60 mmol/L [K ⁺ ] _o . Conversely, blocking SK _Ca /IK _Ca (apamin+charybdotoxin) depolarized cells by ≈10 mV and enhanced electrical conduction (ie, changes in V _m ) by ≈30% ( P <0.05). Conclusions:: These findings illustrate a novel role for SK _Ca /IK _Ca activity in tuning electrical conduction along the endothelium of resistance vessels by governing signal dissipation through changes in membrane resistance. Voltage-insensitive ion channels can thereby tune intercellular electrical signaling independent from gap junction channels.

BACKGROUND AND PURPOSE Electrical conduction along endothelium of resistance vessels has not been determined independently of the influence of smooth muscle, surrounding tissue or blood. Two interrelated hypotheses were tested: (i) Intercellular conduction of electrical signals is manifest in endothelial cell (EC) tubes; and (ii) Inhibitors of gap junction channels (GJCs) have confounding actions on EC electrical and Ca²⁺ signalling.EXPERIMENTAL APPROACH Intact EC tubes were isolated from abdominal muscle feed (superior epigastric) arteries of C57BL/6 mice. Hyperpolarization was initiated with indirect (ACh) and direct (NS309) stimulation of intermediate‐ and small‐conductance Ca²⁺‐activated K⁺ channels (IK_Ca/SK_Ca). Remote membrane potential (V_m) responses to intracellular current injection defined the length constant (λ) for electrical conduction. Dye coupling was evaluated following intracellular microinjection of propidium iodide. Intracellular Ca²⁺ dynamics were determined using Fura‐2 photometry. Carbenoxolone (CBX) or β‐glycyrrhetinic acid (βGA) was used to investigate the role of GJCs.KEY RESULTS Steady‐state V_m of ECs was −25 mV. ACh and NS309 hyperpolarized ECs by −40 and −60 mV respectively. Electrical conduction decayed monoexponentially with distance (λ∼1.4 mm). Propidium iodide injected into one EC spread into surrounding ECs. CBX or βGA inhibited dye transfer, electrical conduction and EC hyperpolarization reversibly. Both agents elevated resting Ca²⁺ while βGA inhibited responses to ACh.CONCLUSIONS AND IMPLICATIONS Individual cells were effectively coupled to each other within EC tubes. Inhibiting GJCs with glycyrrhetinic acid derivatives blocked hyperpolarization mediated by IK_Ca/SK_Ca channels, regardless of Ca²⁺ signalling, obviating use of these agents in distinguishing key determinants of electrical conduction along the endothelium.

Summary: Calcium ions represent universal second messengers within neuronal cells integrating multiple cellular functions, such as release of neurotransmitters, gene expression, proliferation, excitability, and regulation of cell death or apoptotic pathways. The magnitude, duration and shape of stimulation‐evoked intracellular calcium ([Ca²⁺]i) transients are determined by a complex interplay of mechanisms that modulate stimulation‐evoked rises in [Ca²⁺]i that occur with normal neuronal function. Disruption of any of these mechanisms may have implications for the function and health of peripheral neurones during the aging process. This review focuses on the impact of advancing age on the overall function of peripheral adrenergic neurones and how these changes in function may be linked to age‐related changes in modulation of [Ca²⁺]i regulation. The data in this review suggest that normal aging in peripheral autonomic neurones is a subtle process and does not always result in dramatic deterioration in their function. We present studies that support the idea that in order to maintain cell viability peripheral neurones are able to compensate for an age‐related decline in the function of at least one of the neuronal calcium‐buffering systems, smooth endoplasmic reticulum calcium ATPases, by increased function of other calcium‐buffering systems, namely, the mitochondria and plasmalemma calcium extrusion. Increased mitochondrial calcium uptake may represent a ‘weak point’ in cellular compensation as this over time may contribute to cell death. In addition, we present more recent studies on [Ca²⁺]i regulation in the form of the modulation of release of calcium from smooth endoplasmic reticulum calcium stores. These studies suggest that the contribution of the release of calcium from smooth endoplasmic reticulum calcium stores is altered with age through a combination of altered ryanodine receptor levels and modulation of these receptors by neuronal nitric oxide containing neurones.