Different sensitivities to cholinergic and adrenergic stimulations in rat parotid

Objective: Salivary gland function is regulated by the autonomic nervous system, which innervates both salivary acinar and ductal cells. In both the salivary acinar and ductal cells, cholinergic and adrenergic stimulations increase intracellular Ca²⁺ concentration ([Ca²⁺]_i). However, there is no systematical study comparing sensitivity to the cholinergic and adrenergic drugs between parotid acini and ducts. The purpose of this study was to examine different sensitivities to cholinergic and adrenergic stimulation in rat parotid acini and ducts.

Methods: Cholinergic and adrenergic drugs-induced changes of [Ca²⁺]_i were investigated in cells of fura-2-loaded digested rat parotid acini and ducts, by using Ca²⁺-imaging technique.

Results: Carbachol (CCh) at 1 μM increased more [Ca²⁺]_i in parotid acini than ducts whereas noradrenaline (NA) at 1 μM conversely increased less [Ca²⁺]_i in acini than ducts. CCh-induced Ca²⁺ responses in both acini and ducts were blocked by a M3 receptor selective antagonist (4-diphenyl-acetoxy-N-methylpiperidine methiodide: 100 nM). NA-induced Ca²⁺ response in acini was completely blocked by an α1 receptor selective antagonist (phentolamine: 100 nM) and the response in ducts was partially inhibited by the antagonist. The phentolamine-resistance response in ducts was completely blocked by a β receptor selective antagonist (propranolol: 1 μM) and a β selective agonist (isoproterenol: 10-100 μM) induced an increment of [Ca²⁺]_i in ducts, but not acini.

Conclusions: These results suggest that there are different sensitivitiies to cholinergic and adrenergic agonists between parotid acini and ducts.