Q. Regarding electrolyte absorption:
1. cholera toxin binds to adenosine diphosphate ribose to the subunit of Gs, stimulative ATPase activity
2. active transport of Na+ into the small intestine enterocytes is coupled with the absorption of glucose
3. magnesium sulphate absorption is coupled with Na+ -K+ -ATPase pump
4. the Na+ -K+ ATPase pumps are located at the luminal membrane of the enterocyte
- e.