Cytoplasmic Ca2+ signalling and reduction of mitochondrial pyridine nucleotides in adrenal glomerulosa cells in response to K+, angiotensin II and vasopressin

Abstract

We have examined the mitochondrial formation of NAD(P)H in rat adrenal glomerulosa cells. A short-term elevation of the K+ concentration from 3.6 to 8.4 mM induced a reversible increase in the formation of reduced pyridine nucleotides. Potassium applied after the addition of rotenone had no further effect, confirming that the redox signal was of mitochondrial origin. Inhibition of aldosterone synthesis by aminoglutethimide in K+-stimulated cells decreased the rate of decay of the NAD(P)H signal upon the termination of stimulation, indicating that the NADPH formed was consumed in aldosterone synthesis. When the NAD(P)H signal was measured simultaneously with the cytoplasmic free Ca2+ concentration ([Ca2+]i), elevation of the K+ concentration to 6.6 or 8.4 mM induced parallel increases in [Ca2+]i and NAD(P)H formation. The rates of increase and decrease of NAD(P)H were lower than for [Ca2+]i, confirming that the redox signal was secondary to the Ca2+ signal. Angiotensin II (100 pM-1 nM) induced an oscillatory NAD(P)H signal which usually returned to a lower baseline concentration, while a sustained signal with superimposed oscillations was observed at higher concentrations. Simultaneous measurements showed that NAD(P)H levels followed the [Ca2+]i pattern evoked by angiotensin II. Vasopressin (100 nM) also induced parallel oscillations of [Ca2+]i and NAD(P)H. A sustained rise in the extramitochondrial Ca2+ concentration to 1 microM induced a sustained elevation of the intramitochondrial Ca2+ concentration in permeabilized cells, as measured with rhod-2. A sustained rise in [Ca2+]i evoked by long-term stimulation with 8.4 mM K+ or 2.5 nM angiotensin II resulted in sustained NAD(P)H production. These Ca2+-dependent changes in the mitochondrial redox state support the biological response, i.e. aldosterone secretion by glomerulosa cells.

Calcium-dependent mitochondrial cAMP production enhances aldosterone secretion

“…More specifically, we here demonstrate that: i) angiotensin II, an agonist known to induce (often oscillatory) increases in cytosolic and mitochondrial Ca 2+ (Brandenburger et al, 1996;Lalevee et al, 2003;Spät and Hunyady, 2004;Spät and Pitter, 2004), as well as reduction in pyridine nucleotides (Pralong et al, 1992;Pralong et al, 1994;Rohács et al, 1997), also causes a dose dependent rise in mt-cAMP; ii) the effects of angiotensin II on mt-cAMP are reduced by buffering matrix Ca 2+ increases caused by the expression of mitoS100G (Wiederkehr et al, 2011), by siRNA reduction in sAC expression or by the sAC inhibitor 2-OHE and are augmented by the PDE2A inhibitor EHNA; iii) a clear increase in mt-cAMP is also caused by the well known sAC activator, bicarbonate (Buck et al, 1999;Jaiswal and Conti, 2003;Litvin et al, 2003;Steegborn et al, 2005b). Three lines of evidence support the conclusion that sAC is primarily localized in the mitochondria: i) the majority of the protein band (molecular weight 50 kDa), revealed in lysates of H295R cells by immunoblotting with anti-sAC antibodies and corresponding to the truncated, fully active form of sAC (Buck et al, 1999), remained in the pellet after plasma membrane permeabilization with digitonin; ii) the mitochondrial cAMP sensor 4mtH30 and the cytosolic sensor H30 responded with opposite signals to bicarbonate addition, i.e.…”

“…Calcium ions exert intramitochondrial action(s) as well. By activating mitochondrial dehydrogenases (McCormack et al, 1990), elevation of mitochondrial matrix [Ca 2+ ] enhances the formation of reduced pyridine nucleotides in rat (Pralong et al, 1992;Pralong et al, 1994) and human (Rohács et al, 1997;Spät et al, 2012) glomerulosa cells. This effect contributes to the enhancement of aldosterone secretion in cells from both species (Spät et al, 2012;Wiederkehr et al, 2011).…”

Meta analysis of angiotensin-converting enzyme I/D polymorphism as a risk factor for preeclampsia in Chinese women

“…A common 287-bp Alu repeat sequence insertion or deletion (I/D) within intron 16 in the ACE gene has been reliably associated with substantial differences in the plasma ACE concentration, whereas the mean plasma ACE level of DD subjects was about twice that of II individuals (Tiret et al, 1992). Thus, the polymorphism has been considered a strong candidate for PE risk; however, a number of contradictory findings have been reported (Rohacs et al, 1997;Bouba et al, 2003;Galao et al, 2004;Kaur et al, 2005). The inconsistency of results has been attributed to insufficient statistical power caused by small sample size.…”

Mitochondrial Ca2+ Uptake Requires Sustained Ca2+ Release from the Endoplasmic Reticulum

“…Among them, a well known example is the regulation of mitochondrial enzymes involved in ATP production or steroid synthesis, where Ca 2ϩ taken up from microdomains generated at the mouth of ER Ca 2ϩ release channels plays a fundamental role (15,31). A transient [Ca 2ϩ ] m peak was shown to exert a long term effect at the level of ATP synthesis (32), and continuous mitochondrial [Ca 2ϩ ] elevation, even at relatively lower extramitochondrial Ca 2ϩ levels, was shown to increase the activity of dehydrogenases of the Krebs cycle (13,33,34), thus elevating the NADH level and the activity of the electron transport chain. At the same time, Ca 2ϩ uptake by mitochondria has been shown to be involved in a radically different process (i.e.…”