IONIC COMPONENTS OF THE ELECTRICAL RESPONSE OF CHROMAFFIN CELLS FROM THE TOAD (CAUDIVERBERA-CAUDIVERBERA) ADRENAL-GLAND

1. Ultra fine tip microelectrodes (300 MOhm) were used to study the el ectrical properties of the chromaffin cell membrane in situ in the int act toad adrenal gland. 2. In the presence of physiologic [K+]o (2 mM) the resting membrane potential (V(m)) was -53 +/- 3.2 mV. V(m) depend ed on [K+]o as predicted by the constant field equation with P(Na)/P(K ) of 0.16. 3. A small fraction (20%) of the impaled cells exhibited sp ontaneous electrical activity, though in all the cells examined, the i njection of depolarizing current pulses elicited repetitive spikes. 4. Our measurements of the chromaffin cell input resistance (326 +/- 35 MOhm) is substantially smaller than the values reported for bovine iso lated chromaffin cells, suggesting that the toad adrenal chromaffin ce lls might be electrically coupled. 5. Tetraethylammonium (TEA) increas ed the amplitude and duration of spikes, probably inhibiting outward K + current. In the presence of tetrodotoxin (TTX) action potentials wer e abolished, although they reappeared if TEA was added, suggesting the participation of both Na+ and Ca2+ currents in the genesis of spikes. 6. As expected, acetylcholine (ACh) and nicotine depolarized the cell s, though they did not always elicit electrical activity. 7. Muscarine (10-100 muM) had no effect on both V(m) and on the depolarization ind uced by ACh or nicotine. Since muscarine inhibits catecholamine (CA) s ecretion induced by ACh and nicotine, we concluded that the inhibition of CA release by muscarine in the toad probably occurs at a level oth er than the membrane.