QUANTITATIVE ESTIMATION OF THE AREA OF LUMINAL AND BASOLATERAL MEMBRANES OF RAT PAROTID ACINAR COILS - SOME PHYSIOLOGICAL APPLICATIONS

Knowledge of luminal and basolateral acinar cell membrane areas of the secretory endpieces is a prerequisite for a detailed quantitative ana lysis of the ion transport involved in secretion of the primary saliva . In the present study, these areas were estimated in rat parotid acin ar cells using standard stereological methods. A total of 480 microgra phs - obtained by random sampling from eight glands from four rats - w ere analysed at a final magnification of 40000x. Expressed per unit ce ll volume, the area of the luminal acinar cell membrane was: 0.125 mu m(2).mu m(-3) (SEM=0.027 mu m(2).mu m(-3), n=4 animals) and the area o f the basolateral membrane was: 1.54 mu m(2).mu m(-3) (SEM=0.085 mu m( 2).mu m(-3), n=4 animals). These figures make it possible to perform a synthesis based upon different categories of experimental data, e.g. on ion fluxes, membrane potentials and single-channel conductances. Th us, we have estimated the density of open, low-conductance Cl- channel s in the luminal membrane - which are not readily accessible for direc t, patch-clamp analysis - to be approximately 18 channels per mu m(2) in the stimulated state.