<Li> phosphorylate phosphofructokinase 2 (stimulating it, cardiomyocytes only) </Li> <Tr> <Td> myocyte (cardiac muscle) </Td> <Td> cardiovascular </Td> <Td> <Ul> <Li> norepinephrine → β - adrenergic receptor </Li> </Ul> </Td> <Td> </Td> <Td> <Ul> <Li> sequester Ca in sarcoplasmic reticulum <Ul> <Li> phosphorylates phospholamban </Li> </Ul> </Li> </Ul> </Td> </Tr> <Ul> <Li> norepinephrine → β - adrenergic receptor </Li> </Ul> <Li> norepinephrine → β - adrenergic receptor </Li>

What is the significance of signal pathways using protein kinase a