Evidence for acetylcholine receptor blockade by intracellular hydrogen ions in cultured chick myoballs.

Acetylcholine (ACh)-induced membrane currents were recorded in voltage-clamped myoballs in culture. The ACh sensitivity and the charge transfer per channel (Qc) were doubled in NH4+ at normal extracellular pH (pHo). Immediately after wash-out of NH4+, the ACh sensitivity and Qc undershot below the control. The recovery period of the ACh sensitivity and Qc was about 20 min. The ACh sensitivity and Qc greatly increased at alkaline pHo and decreased at acid pHo. We suggest that the intracellular H+ ions can block the ACh-induced channel. The pHo effects may be mediated by a similar (but smaller) change in the intracellular pH (pHi). Intracellular alkalinization can improve the channel function.