REGULATION OF CELL-VOLUME AND DIFFUSION OF INTRACELLULAR WATER IN SALIVARY ACINAR-CELLS

The regulation of acinar cell volume and the properties of intracellul ar water were investigated in perfused rat mandibular salivary glands by proton nuclear magnetic resonance (NMR) spectroscopy. Using an inve rsion-recovery pulse sequence, and an extracellular relaxation reagent (10 mM Gd-DTPA) to suppress the proton NMR signal from extracellular water, acinar cell volume (intracellular water content) in unstimulate d glands was shown to depend upon Cl- uptake by basolateral Na+K+-2Cl( -) cotransport. Muscarinic and P-adrenoceptor stimulation induced shri nkage and swelling respectively. In pulsed-field-gradient NMR experime nts, the diffusion coefficient of intracellular water was found to be more than an order of magnitude smaller than that of extracellular wat er. Using this intrinsic difference in diffusivity between the two com partments, cell volume regulation was investigated in intact, perfused glands in the absence of relaxation reagents. Using both NMR techniqu es, acinar cells in perfused glands were observed to behave like simpl e osmometers in response to anisosmotic media, and did not show the vo lume regulatory responses described in dissociated acinar cells.