Effects of adrenergic neurotransmitter on K transport in superfused segments of rat submaxillary gland

The effect of the adrenergic neurotransmitter on K transport in the segments isolated from the rat submaxillary gland was investigated, employing the technique of electrical field stimulation (FS) and applying tyramine, a releasing drug for the catecholaminergic neurotansmitter. FS (16 Hz, 2 ms and 80 V for 1 min) caused a K release (peak value, 1.0 μmol/g/min) followed by a K uptake (peak value, 0.4 μmol/g/min) in the absence of any autonomic antagonist. Both FS-induced K release and uptake were blocked by the addition of tetrodotoxin (10^-7 g/ml). In the presence of atropine (1.4×10^-6 M), FS caused only a transient K uptake, which was abolished by the superimposed addition of propranolol (5×10^-6 M). Application of tyramine (6×10^-6-6×10^-4 M) always only caused K uptake (peak value, 0.96 μmol/g/min), which was abolished by the addition of propranolol. The K uptake evoked either by FS or by tyramine application in the presence of atropine was not seen in the segments from rats pretreated (i.p.) with 6-hydroxydopamine. These results suggest that the adrenergic neurotransmitter activates mainly a β-adrenergic receptor and evokes K uptake through receptor activation.