Effects of divalent cations on acetylcholine-evoked membrane potential in the ionophore A23187 treated mouse pancreas.

Membrane potential and resistance were measured in isolated segments of mouse pancreas superfused in vitro using two intracellular microelectrodes. The acinar cells were stimulated by microionophoretic ACh application from an extracellular AChCl filled micropipette. The membrane depolarization and resistance reduction evoked by short pulses of ACh stimulation were abolished by treatment with A23187 containing Ca-free solution. The subsequent exposure of the A23187-treated tissue to a Ca or Sr containing solution restored the responses to short pulses of ACh. Addition of Ba, Co, or Mn instead of Ca had no such restorative effects. Mn or Co markedly suppressed the restorative effects of Ca or Sr. It is concluded that A23187 treatment causes depletion of intracellular Ca stores. The restorative effect of Ca or Sr indicates that short pulses of ACh stimulation evoke an increase in intracellular Ca or Sr concentration. Short pulses of ACh seem to release Ca from the stimulant-sensitive Ca pool and, in addition, to increase the membrane Ca permeability.