Module 7: Figure chromaffin cell secretion
Chromaffin cell stimulus–secretion coupling.
The splanchnic nerve that innervates chromaffin cells release acetylcholine (ACh) that activates the nicotinic acetylcholine receptor (nAChR) that gates Na+, causing the membrane to depolarize (ΔV) sufficiently to trigger action potentials that sweep around the cell to activate voltage-operated channels (VOCs) such as the P/Q channels. Entry of external Ca2+ creates a microdomain of Ca2+ that triggers exocytosis and the release of chromaffin granule contents that contain adrenaline (epinephrine), opiates, ATP and chromogranins. The opiates and ATP can feed back to activate receptors that use the G protein subunit Gαi to inhibit the entry channels. The Ca2+ signal is amplified by stimulating the ryanodine receptors (RYRs) to release Ca2+ from the internal stores.