AQP2 and Hyponatremia: On the other hand, aquaporin 2 expression in the collecting tubules is enhanced in leptospirosis kidneys compared to non-leptospirosis kidneys [24].Therefore, although hyponatremia and hypokalemia can separately occur in many tropical diseases [25, 26] hyponatremia together with hypokalemia was characteristically found in leptospirosis (Fig 2).