G6PD and hyperinsulinemic hypoglycemia, familial, 4: To test that idea and to shed light on the role played by G6PD and NADPH in regulating L-type Ca2+ channel and heart function, we studied the effects of 6-aminonicotinamide (6AN), a competitive G6PD inhibitor [15], and G6PD deficiency on cardiac metabolism and function, and L-type Ca2+ activity in isolated cardiac myocytes.