Regulation of Na(+)-3HCO3- cotransport in rabbit proximal convoluted tubule via adenosine A1 receptor.
We investigated the role of adenosine A1-receptor in the regulation of basolateral Na(+)-3HCO3- cotransporter in the rabbit proximal convoluted tubule (PCT) microperfused in vitro by monitoring basolateral membrane potential and intracellular pH. FK-453, a highly specific A1 antagonist, inhibited basolateral HCO3- conductance in a concentration-dependent manner (10(-10)-10(-5) M). Other A1 antagonists, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) at 10(-5) M and theophylline at 10(-3) M, also had similar effects. N6-cyclohexyladenosine (CHA) at 10(-7) M attenuated the effect of low concentration (10(-8) M) of FK-453. Either enhancement of the degradation of adenosine by 0.1 U/ml adenosine deaminase (ADA) or inhibition of adenosine release from the cells by 10(-6) M S-(4-nitrobenzyl)-6-thioinosine (NBTI) mimicked the effects of A1 antagonists. These observations suggest that endogenous adenosine is released from PCT cells and stimulates Na(+)-3HCO3- cotransporter. Both 10(-4) M 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate (CPT-cAMP) and 10(-6) M forskolin also inhibited basolateral HCO3- conductance. Both 10(-6) M FK-453 and 10(-4) M CPT-cAMP decreased the initial rate as well as the magnitude of intracellular acidification induced by reduction of peritubular HCO3- concentration from 25 to 0 mM. Neither 10(-6) M FK-453 nor 10(-7) M CHA changed intracellular Ca2+ concentration as measured by fura-2 fluorescence. These results indicate that adenosine might stimulate HCO3- exit across the basolateral membrane through Na(+)-3HCO3- cotransporter by decreasing intracellular cAMP via A1-receptor activation.(ABSTRACT TRUNCATED AT 250 WORDS)
Takeda
M
M
Department of Pharmacology, Jichi Medical School, Tochigi, Japan.
Yoshitomi
K
K
Imai
M
M
D000241:Adenosine / Q000037:antagonists & inhibitors; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D004553:Electric Conductivity; D006863:Hydrogen-Ion Concentration; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D008297:Male; D011817:Rabbits; D018047:Receptors, Purinergic P1 / Q000145:classification / Q000502:physiology*; D015290:Second Messenger Systems; D027982:Sodium-Bicarbonate Symporters
D001639:Bicarbonates; D002352:Carrier Proteins; D018047:Receptors, Purinergic P1; D027982:Sodium-Bicarbonate Symporters; D000241:Adenosine