Nervous control of membrane conductance in mouse lacrimal acinar cells

Abstract

Intracellular microelectrode recordings were made from superfused in vitro preparations of mouse lacrimal giand. The lacrimal acinar cell had a mean resting membrane potential of −44.1±0.5 mV and a mean input resistance of 3.5±0.15 MΩ. Electrical field stimulation (FS) had similar effects to ACh applied by microionophoresis, both evoking a biphasic membrane hyperpolarization (up to 15 mV) accompanied by a reduction in input resistance. The equilibrium potential values (E_FS and E_ACh) for the responses to brief duration FS and ACh ionophoresis ranged between −45 and −75 mV and depended on the time at which measurements were made following the onset of stimulation. Superfusion of ACh or adrenaline also caused membrane hyperpolarization and increased membrane conductance. Estimations of E_FS and E_ACh made during prolonged periods of FS and ACh superfusion yielded mean values of −53.9±1.9 mV and −53.4±1.5 mV respectively. FS evoked a response in all preparations tested with maximal effects seen at 40 Hz frequency. The mean latency of the FS-evoked hyperpolarization (40 Hz) was 270±21 ms and that for the ACh ionophoretic response was 400±65 ms. Low frequency FS (0.5–5 Hz) also induced membrane hyperpolarization and responses to single shock stimuli were occasionally observed. The FS-evoked hyperpolarization was abolished following the blockade of nerve conduction by superfusion of either Na-free or tetrodotoxin-containing media. Effects of FS were not seen in the presence of atropine. Neostigmine potentiated the FS- and ACh-evoked hyperpolarizations. Spontaneous miniature hyperpolarizations were unaffected by tetrodotoxin but abolished by atropine. It is concluded that FS excites a well developed cholinergic innervation of the mouse lacrimal gland resulting in ACh release and acinar cell hyperpolarization. ACh, which appears to be the only neurotransmitter released, mediates its effects by increasing plasma membrane permeability to mainly K ions.