Role of ATP‐sensitive K+ channels in glucose sensing by immortalized adrenomedullary chromaffin cells

Adrenomedullary chromaffin cells exhibit a critical Ca 2+ ‐dependent catecholamine secretion when directly exposed to perinatal stressors (e.g. hypoxia). Using an immortalized chromaffin cell line (MAH), we investigated their potential sensitivity to low glucose (hypoglycemia) by monitoring changes in intracellular free calcium ([Ca 2+ ] i ) with the fluorescent probe Fura‐2. The majority of MAH cells (86%; n=398) were unresponsive on switching from 10 to 0 mM glucose. Interestingly, 0 glucose markedly inhibited (~75%) the rise in [Ca 2+ ] i induced by the depolarizing stimulus high K + (10 mM). To test the possibility that this was due to K ATP channel activation, the K ATP channel blocker, glibenclamide (50 μM), was used. In normal K + , glibenclamide increased the proportion of 0 glucose‐responsive cells from 14% to 65%, and the mean Δ[Ca 2+ ] i response increased fourfold. RT‐PCR and Western blot analysis confirmed the presence of both the inward rectifying (Kir6.2) and sulfonylurea (Sur1) subunits of K ATP channels. These findings suggest that hypoglycemia‐induced activation of K ATP channels may limit [Ca 2+ ] i increases and catecholamine secretion in chromaffin cells. Furthermore, the increased proportion of 0 glucose‐responsive cells in the presence of glibenclamide suggests that hypoglycemia causes a separate excitatory pathway in MAH cells. Supported by NSERC and the HSFO.