Mouse pancreatic acinar cells: effects of electrical field stimulation on membrane potential and resistance.

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Abstract
Intracellular micro-electrode recordings of acinar cell membrane potential and resistance were made from the mouse pancreas superfused in vitro. The acinar cells under investigation were stimulated by electrical field stimulation using 2 Pt wire electrodes and by micro-ionophoretic acetylcholine (ACh) application from an extracellular AChCl-filled micro-electrode. Field stimulation evoked membrane depolarization and reduction in input resistance. Maximal effects were observed at 20-40 Hz frequency, 1-2 ms pulse width and 8-20 V amplitude. The mean latency for the field stimulation-evoked depolarization was 900 ms. Field stimulation responses were seen at low frequency levels of stimulation, the majority of cells responding at 5 Hz and some at 2 Hz. The physiological significance of the low frequency stimulation is discussed. The field stimulation effects resembled those induced by ACh ionophoresis and were abolished by atropine. The equilibrium potentials for both field stimulation and ACh ionophoresis were identical at about -15 mV. The field stimulation response was selectively abolished by tetrodotoxin and by superfusion with Na-free or Ca-free media, while the ACh ionophoretic response persisted. Field stimulation therefore initiated nerve action potentials and consequent ACh release. Spontaneous miniature depolarizaitons observed in some preparations were not abolished by tetrodotoxin and would therefore seem to be a result of quantal release of ACh from nerve terminals. There is no indication from the present studies of the existence of neurotransmitters other than ACh. No inhibitory effects were observed. All preparations studied to date have responded to field stimulation; all acinar cells are potentially under cholinergic neural influence.