Glucosensing in an immortalized adrenomedullary chromaffin cell line: Role of ATP-sensitive K + channels

Abstract

Using an immortalized adrenal chromaffin cell line (MAH cells), we investigated the cellular mechanisms underlying sensitivity to glucose-free solution (aglycemia) using ratiometric Ca 2+ imaging and whole-cell recording. Though few cells (<15%) responded to aglycemia with an increase in intracellular-free Ca 2+ concentration ([Ca 2+] i), in most cells (∼75%), aglycemia caused >50% suppression of the Δ[Ca 2+] i induced by the depolarizing stimulus, high (10 mM) K +. Moreover, in normal K +, the average aglycemia-induced rise in C a i 2 + as well as the proportion of aglycemia-responsive cells increased in the presence of the K ATP channel blocker, glibenclamide. During membrane potential ( V m) measurements, aglycemia induced either hyperpolarization (6/20), depolarization (4/20) or no change in V m. RT-PCR and Western blotting confirmed the presence of K ATP channel subunits Kir6.2 and SUR1 in MAH cells. These findings suggest a dual inhibitory and excitatory action of aglycemia in MAH cells, where activation of K ATP channels effectively inhibits or blunts the Δ[Ca 2+] i due to the excitatory effect. Thus, this cell line appears as an attractive model for studying the molecular mechanisms of glucosensing.