Na+ influx mechanisms in submandibular salivary cells of newborn rats

Carbachol-induced oxygen consumption in slices from developing rat submandibular and parotid glands

In contrast to the submandibular gland, the developing rat parotid gland shows refractoriness to cholinergic secretagogues until 2 wks of age. To assess the underlining mechanism of this refractoriness, I investigated changes in oxygen consumption as a function of animal age in slices from rat submandibular and parotid glands, measuring both basal and carbachol-stimulated levels. The oxygen consumption was determined by a direct manometric method in the Warburg apparatus. Carbachol-induced oxygen uptake in submandibular gland slices was observed by 1 day of age and reached the adult level of stimulation by 3 wks of age. In the parotid gland, carbachol failed to stimulate oxygen uptake in the early post-natal period, and the first response was detected at 2 wks of age, reaching the adult level at 4 wks of age. Para-fluorohexahydro-sila-diphenidol (pFHHSiD), a selective M3 antagonist, inhibited carbachol-induced oxygen uptake in both glands, while pirenzepine, a selective M1 antagonist, had no effect, suggesting that the M3 muscarinic receptors are involved in this process. The respiratory effect of carbachol, in both glands, was inhibitable by ouabain and, to a lesser extent, by furosemide, indicating that carbachol-enhanced oxygen uptake is due to Na,K-ATPase and that the furosemide-sensitive co-transport of Na+ entry is underdeveloped in immature cells. The ouabain-sensitive Na,K-ATPase activity in the parotid gland increased from birth until 28 days of age. At the time of parotid gland refractoriness to carbachol, Ca2+ ionophore A23187 caused an increase of oxygen uptake only in the presence of extracellular Ca2+. In the presence of carbachol, the effect of ionophore was significantly higher than that of ionophore alone. These results raise the possibility that the refractoriness of the parotid gland to carbachol is due to the inability of carbachol to increase Ca2+ uptake rather than to the lack of distal limb, which resides on the pathway from receptor stimulation to Na,K-ATPase activation.

Intracellular pH changes induced by exposure to weak acids and bases in submandibular cells of early postnatal rats

The intracellular pH of submandibular cells of adult, 1-day-old and 1-week-old rats was measured with the pH sensitive fluorimetric indicator SNARF-1, following shifts induced by exposure to a weak acid (sodium butyrate) or a weak base (NH4Cl). The effects of several ion transport inhibitors and agonists on both the pH change and the rate of recovery were examined. The results indicate that, in most respects, the processes involved in pH regulation were similar in the neonatal and mature cells. However, cholinergic and peptidergic stimulation accelerated recovery from sodium butyrate-induced acidification more, and from NH4Cl-induced alkalinization less, in cell preparations from 1-day-old animals.