Alpha 1-adrenoceptor subtypes mediating stimulation of Na+,K(+)-ATPase activity in rat renal proximal tubules.

Although both alpha 1A- and alpha 1B-adrenoceptors are present in renal proximal tubules, the involvement of these receptor subtypes in the stimulation of Na+,K(+)-ATPase activity is not known. This study was undertaken to delineate the receptor subtype(s) involved in alpha 1-adrenoceptor-mediated increase in Na+,K(+)-ATPase activity and to identify the cellular signaling mechanisms such as stimulation of inositol triphosphate formation (IP3) and protein kinase C activation in this phenomenon. It was found that norepinephrine-induced increase in Na+,K(+)-ATPase activity was attenuated by prazosin, but not by rauwolscine, indicating the involvement of alpha 1-adrenoceptors. Furthermore, this response was selectively inhibited by the alpha 1B-adrenoceptor inactivator, chloroethylclonidine (100 microM), but not by the alpha 1A-adrenoceptor antagonist, WB4101 (0.01 microM). We examined whether these effects on Na+,K(+)-ATPase activity are mediated via the activation of IP3 and protein kinase C. Phenylephrine-induced increase in IP3 levels was abolished by prazosin, and significantly inhibited by WB4101, but not by chloroethylclonidine. Similarly, phenylephrine-induced activation of protein kinase C was sensitive to blockade by WB4101, but not by chloroethylclonidine. These results suggest that whereas both alpha 1A- and alpha 1B-adrenoceptors are present in proximal tubules, alpha 1B-adrenoceptors are involved in stimulating Na+,K(+)-ATPase activity and alpha 1A-adrenoceptors are predominantly linked to renal tubular IP3 production and protein kinase C activation. Therefore, it appears that norepinephrine-induced stimulation of Na+,K(+)-ATPase activity does not involve phospholipase-C-coupled protein kinase C pathway.