Facilitation of noradrenaline release by gallamine in the rat salivary gland

Abstract

The effect of gallamine on spontaneous and stimulation-evoked overflow of tritium was studied in the submandibular gland of the rat. The gland was perfused retrogradely and labeled with 3H-noradrenaline. The stimulation-evoked (1 Hz for 60 s) overflow of tritium was facilitated by increasing concentrations of gallamine (0.3-20 mM). None of the concentrations of gallamine increased the spontaneous overflow of the tritium. The facilitatory effect of gallamine was observed in 0.3 to 5 mM calcium medium; the maximum facilitation was observed at the normal concentration of calcium (2.5 mM). The facilitatory effect of gallamine was inversely related to the frequency of stimulation (10-fold facilitation at 1 Hz and 3-fold at 10 Hz). Stimulation of the salivary gland by a single pulse (1 ms duration) in the normal medium did not evoke an overflow of tritium; however, the same stimulus produced a marked increase in the overflow in the presence of gallamine. The facilitatory action of gallamine on the release of sympathetic transmitter is ascribed to the enhanced availability of calcium ions to the secretory process resulting from blockade of potassium conductance during nerve activity.