Differentiation of slow potentials and spikes in longitudinal muscle of cat intestine

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Abstract
Intracellular records from longitudinal muscle of jejunum or duodenum show slow pacemaker potentials, approximately sinuosidal, often with spikes near their peaks. A spike early on a slow wave does not alter its shape but a spike after the peak of the slow wave hastens its decline. Spikes are more sensitive to ionic environment than are slow waves. Potassium depolarizes by 30 mv/log.[K]o; elevated [Ca]o decreases resting potential; in depolarization with either high [K]o or low [Ca]o, spikes are not maintained at membrane potentials less than 32[long dash]35 mv, slow waves not below 25[long dash]27 mv. Spikes were reduced in amplitude at 45% of normal [Na]o (Li+ replacement) and were eliminated in 20% of normal [Na]o (Li+ replacement) or 50% of normal [Na]o (sucrose replacement); slow waves were reduced at 20[long dash]30% [Na]o, eliminated in absence of [Na]o. Critical slow-wave depolarization for spiking approximated 5 mv in all ionic media. It is concluded that slow waves and spikes may be produced by different molecular mechanisms or patches of membrane and by ionic processes which differ quantitatively but not qualitatively.