Alpha 1-adrenoceptors in parotid cells: age does not alter the ratio of alpha 1A and alpha 1B subtypes.

Epinephrine stimulation of 45Ca2+ efflux and inositol 1,4,5-trisphosphate ((1,4,5)IP3) production in parotid cell aggregates from mature rats was greatly inhibited (approximately 70%) by WB 4101 and 5-methylurapidil as compared to a small decrease by chloroethylclonidine (approximately 30%). The combination of WB 4101 or 5-methylurapidil and chloroethylclonidine completely blocked the action of epinephrine. The same relative inhibition was observed with senescent animals. The results suggest (1) that rat parotids contain both alpha 1-adrenoceptor subtypes, i.e., alpha 1A and alpha 1B, in an approximate functional ratio of 70:30, (2) that this relative ratio is not altered during aging, and (3) that both receptors partially mediate 45Ca2+ efflux and (1,4,5)IP3 production in this system.