Glucose-6-phosphate dehydrogenase and NADPH redox regulates cardiac myocyte L-type calcium channel activity and myocardial contractile function.
We recently demonstrated that a 17-ketosteroid, epiandrosterone, attenuates L-type Ca(2+) currents (I(Ca-L)) in cardiac myocytes and inhibits myocardial contractility. Because 17-ketosteroids are known to inhibit glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme in the pentose phosphate pathway, and to reduce intracellular NADPH levels, we hypothesized that inhibition of G6PD could be a novel signaling mechanism which inhibit I(Ca-L) and, therefore, cardiac contractile function. We tested this idea by examining myocardial function in isolated hearts and Ca(2+) channel activity in isolated cardiac myocytes. Myocardial function was tested in Langendorff perfused hearts and I(Ca-L) were recorded in the whole-cell patch configuration by applying double pulses from a holding potential of -80 mV and then normalized to the peak amplitudes of control currents. 6-Aminonicotinamide, a competitive inhibitor of G6PD, increased pCO(2) and decreased pH. Additionally, 6-aminonicotinamide inhibited G6PD activity, reduced NADPH levels, attenuated peak I(Ca-L) amplitudes, and decreased left ventricular developed pressure and ±dp/dt. Finally, dialyzing NADPH into cells from the patch pipette solution attenuated the suppression of I(Ca-L) by 6-aminonicotinamide. Likewise, in G6PD-deficient mice, G6PD insufficiency in the heart decreased GSH-to-GSSG ratio, superoxide, cholesterol and acetyl CoA. In these mice, M-mode echocardiographic findings showed increased diastolic volume and end-diastolic diameter without changes in the fraction shortening. Taken together, these findings suggest that inhibiting G6PD activity and reducing NADPH levels alters metabolism and leads to inhibition of L-type Ca(2+) channel activity. Notably, this pathway may be involved in modulating myocardial contractility under physiological and pathophysiological conditions during which the pentose phosphate pathway-derived NADPH redox is modulated (e.g., ischemia-reperfusion and heart failure).
Department of Biochemistry and Molecular Biology, University of South Alabama, Mobile, Alabama, United States of America.
Dhwajbahadur K
DK
Rawat
Peter
P
Hecker
Makino
M
Watanabe
Sukrutha
S
Chettimada
Richard J
RJ
Levy
Takao
T
Okada
John G
JG
Edwards
Sachin A
SA
Gupte
D015120:6-Aminonicotinamide / Q000494:pharmacology; D000818:Animals; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism*; D004452:Echocardiography; D005954:Glucosephosphate Dehydrogenase / Q000502:physiology*; D005955:Glucosephosphate Dehydrogenase Deficiency / Q000378:metabolism; D008297:Male; D051379:Mice; D009200:Myocardial Contraction / Q000187:drug effects*; D032383:Myocytes, Cardiac / Q000502:physiology; D009249:NADP / Q000502:physiology*; D010427:Pentose Phosphate Pathway / Q000502:physiology; D051381:Rats
D020746:Calcium Channels, L-Type; D015120:6-Aminonicotinamide; D009249:NADP; D005954:Glucosephosphate Dehydrogenase