Key result
In rat juxtaglomerular cells, increasing cAMP with agents like isoproterenol elicited an increase in intracellular free calcium that was approximately 40% of the response induced by angiotensin II.
In rat juxtaglomerular cells, cAMP activates store-operated Ca2+ channels to increase intracellular calcium, which may serve to finely adjust the stimulating effect of cAMP on the renin-angiotensin system.
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Animal data link cAMP to partial Ca2+ mobilization in rat JG cells; leaves open its role in human renin regulation.
The renin-secreting juxtaglomerular cells (JGC) in the media of the afferent arteriole at the vessel pole are the major source of circulating renin. The control of renin secretion is complex with increases in cAMP being the major stimulus and increases in intracellular free Ca2+ concentration ([Ca2+]i) being inhibitory. We measured [Ca2+]i in the afferent arteriole from mostly JGC. Manoeuvres that increase cAMP (e.g. isoproterenol) or dibutyryl-cAMP elicited an increase in [Ca2+]i which was approximately 40% of that induced by angiotensin II (3 nmol/l). The Ca2+ response occurred in 50-90% of the cases, and increasing the stimulus increased responder frequency but not response size. The response was (almost) abolished by removal of extracellular Ca2+, prevented by inhibitors of store-operated Ca2+ channels (Gd3+ and 2-aminoethoxydiphenyl-borate), but was unaffected by isradipine or protein kinase A inhibitors. It was not produced by an activator of EPACs (exchange protein activated by cAMP) and was not accompanied by changes in membrane potential. The data suggest that in rat JGC, cAMP, perhaps directly, activates store-operated Ca2+ channels to increase [Ca2+]i. One could speculate that this increase in [Ca2+]i serves to finely adjust the stimulating effect cAMP-increasing signals on the renin-angiotensin system.
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Laske-Erns et al. (2009) studied this question. cAMP-increasing agents (e.g., isoproterenol, dibutyryl-cAMP) vs. Angiotensin II (3 nmol/l) or baseline was evaluated on Peak increase in fura-2 fluorescence ratio R (intracellular free Ca2+) (37 ± 8% of Angiotensin II response). In rat juxtaglomerular cells, increasing cAMP with agents like isoproterenol elicited an increase in intracellular free calcium that was approximately 40% of the response induced by angiotensin II.
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