Biphasic increasing effect of angiotensin-II on intracellular free calcium in isolated rat early proximal tubule.
In the freshly isolated early proximal tubule (S1), the effect of angiotensin II (ANG II) on cytosolic Ca++ concentration ([Ca++]i) was determined using the fluorescent indicator fura-2. In order to establish an adequate experimental system, we investigated firstly the relationship between cellular ATP and [Ca++]i under various conditions in late proximal tubule, the most fragile nephron segment, and cortical collecting tubule, a relatively stable one. We found out that cellular ATP depletion caused [Ca++]i to rise, and ANG II response to [Ca++]i under high ATP condition was higher than that under low ATP condition. ANG II-induced [Ca++]i rise in S1 was biphasic, demonstrating the two peaks corresponding to the 10(-11) and 10(-7) M ANG II. This study suggests for the first time 1) the necessity of high intracellular ATP to evaluate a high affinity ANG II actions and 2) the biphasic characteristics of [Ca++]i increase by ANG II in intact S1.
Jung
K Y
KY
Department of Pharmacology, Faculty of Medicine, University of Tokyo, Japan.
Endou
H
H
D000255:Adenosine Triphosphate / Q000378:metabolism; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D005456:Fluorescent Dyes; D016257:Fura-2; D007685:Kidney Tubules, Collecting / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains
D001572:Benzofurans; D005456:Fluorescent Dyes; D000804:Angiotensin II; D000255:Adenosine Triphosphate; D002118:Calcium; D016257:Fura-2