Electrophysiological properties of gastrointestinal smooth muscle Resting membrane potential -40~-80mV o lonic basis Em(selective membrane permeability to K, Nat, Ch and Caz+) Electrogenic Nat-K pumpElectrophysiological properties of gastrointestinal smooth muscle  Resting membrane potential  -40~-80 mV  Ionic basis  Em (selective membrane permeability to K+ , Na+ , Cl￾and Ca2+)  Electrogenic Na+ -K+ pump