ABSTRACT
Sympathetic stimulation induces weak salivation compared with parasympathetic stimulation. To clarify this phenomenon in salivary glands, we investigated cAMP-induced modulation of Ca(2+)-activated Cl(-) secretion from rat parotid and submandibular acinar cells because fluid secretion from salivary glands depends on the Cl(-) secretion. Carbachol (Cch), a Ca(2+)-increasing agent, induced hyperpolarization of the cells with oscillatory depolarization in the current clamp mode of the gramicidin-perforated patch recording. In the voltage clamp mode at -80 mV, Cch induced a bumetanide-sensitive oscillatory inward current, which was larger in rat submandibular acinar cells than in parotid acinar cells. Forskolin and IBMX, cAMP-increasing agents, did not induce any marked current, but they evoked a small nonoscillatory inward current in the presence of Cch and suppressed the Cch-induced oscillatory inward current in all parotid acinar cells and half (56%) of submandibular acinar cells. In the current clamp mode, forskolin + IBMX evoked a small nonoscillatory depolarization in the presence of Cch and reduced the amplitude of Cch-induced oscillatory depolarization in both acinar cells. The oscillatory inward current estimated at the depolarized membrane potential was suppressed by forskolin + IBMX. These results indicate that cAMP suppresses Ca(2+)-activated oscillatory Cl(-) secretion of parotid and submandibular acinar cells at -80 mV and possibly at the membrane potential during Cch stimulation. The suppression may result in the weak salivation induced by sympathetic stimulation.
