Effect of adenosine on membrane potential and Ca2+ in juxtaglomerular cells. Comparison with angiotensin II.
BACKGROUND
Renin is mainly secreted from the juxtaglomerular cells (JGC) in the kidney situated in the afferent arteriole close to the vessel pole. Angiotensin II (ANG II) and adenosine inhibit renin secretion and synergistically constrict the afferent arteriole. ANG II depolarises JGC and increases the cytoplasmic free Ca2+ concentration [Ca2+]i. The responses of JGC to adenosine are less known.


METHODS
Effects of adenosine on membrane potential and [Ca2+]i were studied in afferent arterioles from NaCl-depleted rats and mice.


RESULTS
Stimulation of A1 adenosine receptors (A1AR) by adenosine (10 microM) or cyclohexyladenosine (1 microM) increased the spiking frequency of JGC, slightly depolarised the cells and, in < or =50% of the cases, increased [Ca2+]i. These effects were much smaller than those of ANG II (3 nM). Simultaneous application of cyclohexyladenosine and ANG II gave only additive effects on [Ca2+]i; in addition, responses to ANG II in JGC from A1AR knockout mice were similar to those from control mice.


CONCLUSIONS
The small changes in membrane potential and [Ca2+]i in response to A1AR stimulation as compared to those of ANG II may suggest that these 2 tissue hormones use different signal transduction mechanisms to affect JGC function, including the inhibition of renin release.
Laske-Ernst
Julia
J
Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Tübingen, Germany.
Stehle
Alexander
A
Vallon
Volker
V
Quast
Ulrich
U
Russ
Ulrich
U
D000241:Adenosine / Q000502:physiology*; D000804:Angiotensin II / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000737:chemistry / Q000502:physiology; D007606:Juxtaglomerular Apparatus / Q000166:cytology* / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D051381:Rats; D017207:Rats, Sprague-Dawley; D018047:Receptors, Purinergic P1 / Q000502:physiology
D018047:Receptors, Purinergic P1; D000804:Angiotensin II; D000241:Adenosine; D002118:Calcium