Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC66
Cannabinoids regulate muscarinic receptor-mediated salivation in submandibular salivary gland
O. Netsyk1, N. Fedirko1
1. Ivan Franko National University of L`viv, L`viv, Ukraine.
The ability of cannabinoids to modulate the activity of other receptor types was shown by many research groups (1). During the tasting and chewing of food under the physiological conditions muscarinic (M) receptors are core to the saliva secretion (2). Besides, CB1Rs are known to inhibit ACh release and modulate an autonomic neurotransmission to the submandibular gland (SMG) (3). Thus, in the present study, we aimed to explore in vivo the effects of CB1/CB2 cannabinoid receptors (CBRs) agonist - WIN 55212-2 (WIN, 5µM) on the M receptor mediated-stimulation of saliva outflow and content provided by rat SMG. We also measured in vitro Ca2+-ATPase activities in the SMG acinar cell`s microsomal fraction upon activation CBRs. The male Wistar rats were anesthetized with i.p. injection of pentobarbital (30-40 mg/kg). Saliva was collected using variable speed peristaltic pump. The salivation was evaluated by saliva flow rate and total proteins concentration in saliva collected from the ducts in oral cavity before and after administration of agonists. SMG cells were isolated by collagenase digestion. Stimulation of salivation with i.p. injection of 0,2 and 2 mg/kg M-receptor agonist pilocarpine and simultaneous intraglandular injection of WIN caused the decrease of the stimulation potency of pilocarpine on the rate of salivation by 40±8% (p<0.01, n=6) and 27±6% (p<0.01, n=5) correspondingly. Even more pronounced inhibitory effect of CBRs activation was shown when both agonists were injected intraglandularly: the WIN-induced suppression of pilocarpine-stimulated effect on salivation was 52±10% (p<0.05, n=6) and 45±4% (p<0.05, n=5) respectively. To evaluate an effect of CBRs activation on ACh-induced salivation, we first applied to the SMG WIN (for 10 min) and subsequently ACh (5µM). Prolonged application of WIN leads to suppression of basal salivation occurring at 5 and 10 min by 38±7% (p<0.05, n=6) and 47±2% (p<0.05, n=5) vs. the saline-treated group respectively. Pretreatment with WIN significantly inhibited the ACh-induced salivation at 5, 10 and 15 min after ACh administration: the saliva flow rate decreased by 48±7% (p<0.05, n=6), 54±13% (p<0.05, n=6) and 49±5% (p<0.05, n=4) vs. the control group respectively. The latter was accompanied by significant increase of the total protein concentration in the secreted saliva at 5, 10 and 15 min by 37±3% (p<0.05, n=5), 58±5% (p<0.05, n=5) and 56±6% (p<0.05, n=5) vs. the control group respectively. Besides, we also showed that CBRs-induced inhibition of the resting salivation is accompanied by the decreased activity of Ca2+-ATPases in endoplasmic reticulum (by 44±6%, p<0.05, n=6) and increased - in plasma membrane (by 26±6%, p<0.05, n=6). These findings revealed the novel function of CBRs as the negative regulators of agonist-induced stimulated salivation that occurs with the changes of the Ca2+ homeostasis in SMG cells.
Where applicable, experiments conform with Society ethical requirements