Temperature-dependent modification of divalent cation flux in the rat parotid gland basolateral membrane.

Divalent cation (Mn2+, Ca2+) entry into rat parotid acinar cells is stimulated by the release of Ca2+ from the internal agonist-sensitive Ca2+ pool via a mechanism which is not yet defined. This study examines the effect of temperature on Mn2+ influx into internal Ca2+ pool-depleted acini (depl-acini, as a result of carbachol stimulation of acini in a Ca(2+)-free medium for 10 min) and passive 45Ca2+ influx in basolateral membrane vesicles (BLMV). Mn2+ entry into depl-acini was decreased when the incubation temperature was lowered from 37 to 4 degrees C. At 4 degrees C, Mn2+ entry appeared to be inactivated since it was not increased by raising extracellular [Mn2+] from 50 microM up to 1 mM. The Arrhenius plot of depletion-activated Mn2+ entry between 37 and 8 degrees C was nonlinear, with a change in the slope at about 21 degrees C. The activation energy (Ea) increased from 10 kcal/mol (Q10 = 1.7) at 21-37 degrees C to 25 kcal/mol (Q10 = 3.0) at 21-8 degrees C. Under the same conditions, Mn2+ entry into basal (unstimulated) cells and ionomycin (5 microM) permeabilized depl-acini exhibit a linear decrease, with Ea of 7.8 kcal/mol (Q10 = 1.5) and 6.2 kcal/mol (Q10 < 1.5), respectively. These data suggest that depletion-activated Mn2+ entry into parotid acini is regulated by a mechanism which is strongly temperature dependent and distinct from Mn2+ entry into unstimulated acini.(ABSTRACT TRUNCATED AT 250 WORDS)