Electrical activity in chromaffin cells of intact mouse adrenal gland

Membrane potentials of medullary chromaffin cells of the adrenal gland of the mouse were measured in situ. Resting potential (-54.3 ± 8.8 mV) depended on extracellular [K⁺] as predicted by the constant-field equation with a permeability ratio, P(Na)/P(K), of 0.09. Current-voltage (I-V) relationships showed that the current is rectified across the chromaffin cell membrane. A rectification ratio of 0.4 was calculated from the slopes of the I-V curves for positive (41 ± 26 MΩ) and negative 103 ± MΩ) currents. Because input resistance for a resting chromaffin cell in isolation is ~50 GΩ, the chromaffin cells in situ behave as if they were electrically coupled. Most cells responded to depolarizing current pulses with repetitive action potentials, but only 50% of them showed spontaneous electrical activity. Spontaneous activity was often seen in the presence of tetrodotoxin (3 μM). Although the application of the K⁺-channel blockers tetraethylammonium and Ba²⁺ greatly increased the amplitudes of the action potentials, only Ba²⁺ induced continuous electrical activity. Application of acetylcholine (ACh) always depolarized the cell membrane. This effect was blocked by atropine but not by D-tubocurarine, suggesting that ACh stimulation by chromaffin cells in the mouse involves activation of muscarinic receptors.