In-vitro release of K+ from the developing submandibular gland of early postnatal rats

The release studied by incubating tissue slices in an enriched, oxygenated medium in the presence and absence of secretagogues indicated that slices from 1-day-old rats released K+ in response to carbamylcholine, but not in response to epinephrine. The response to carbamylcholine was dose-related, with a 12.6 +/- 1.3 per cent release at a concentration of 2 X 10(-5) M. Epinephrine did not induce K+ release in concentrations from 2 X 10(-7) to 2 X 10(-4) M. Glands from 7- and 14-day-old rats released a similar amount as those of newborns in response to carbamylcholine and by 21 days of age the glands released 21.5 +/- 1.9 per cent of their K+ content upon exposure to 2 X 10(-5) M carbamylcholine. A response to epinephrine (2 X 10(-5) M) was first detected at 14 days of age, when the slices released 8.3 +/- 1.2 per cent of their K+. Slices of 21-day-old rats showed a 17.9 +/- 1.3 per cent K+ release in response to this dose. As in adult glands, the net amount of K+ released by the developing postnatal gland seems to be the result of two opposing mechanisms, a passive efflux and an active re-uptake which depends on the activation of an ouabain-sensitive Na+ -K+ -ATPase. The passive efflux component was similar in glands from different postnatal ages and was enhanced by secretagogues. The extent of active uptake, on the other hand, decreased with increasing postnatal age. As in the adult, the net release of K+ depended on the presence of Ca2+ in the incubation medium, but the sensitivity of the response to Ca2+ omission varied in accord with the age of the animals and with the stimulant used. It is speculated that proacinar and terminal tubular cells may be involved in K+ release in the early postnatal period.