Effect of neural stimulation on contractile system (myoepithelial cells) in isolated salivary Gland segments of rat

The effect of cholinergic neural excitation by field stimulation on the tension of the contractile system (myoepithelial cells) was investigated in superfused segments of rat salivary glands (sublingual, submaxillary, and parotid). Electric field stimulation evoked gland tissue contraction of a few mg, which was blocked by addition of TTX or atropine. The order of the magnitude of the contraction per wet tissue weight was sublingual > submaxillary > parotid. This correlates with the order of the distribution of myoepithelial cells described in morphological investigations. Cholinergic stimulants induced contraction in all salivary glands, but adrenergic stimulants hardly evoked contraction in the sublingual gland, whereas those drugs evoked a considerable amount of contraction in the submaxillary gland. These findings seem to suggest that the contraction may originate in the myoepithelial cells. The omission of Na from the superfusing solution quickly abolished the contraction evoked by field stimulation but not the contraction induced by ACh. The omission of Ca from the solution reduced the contraction evoked not only by field stimulation but also by ACh and by high K. The results suggest that extracellular Ca is important for the initiation of myoepithelial contraction.