This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Membrane potiential, Subject name: Physiology
RMP of a smooth muscle cell is: 
Select and explain. 
A. - 10 mV to - 20 mV, B. - 45 mV to - 55 mV, C. - 65 mV to - 75 mV, D. - 85 mV to - 90 mV
B: - 45 mV to - 55 mV
Answer: B: - 45 mV to - 55 mV 
Explanation: The membrane potential of a smooth muscle fiber has no true "resting" value. However, in periods of relative quiescence it is about - 45 to - 55 mV. The reason for this low RMP of smooth muscle, compared to skeletal muscle, is the relatively high intracellular & and relatively low in the smooth muscle.