WHOLE-CELL RECORDING OF THE CA2-DEPENDENT SLOW AFTERHYPERPOLARIZATIONIN HIPPOCAMPAL-NEURONS - EFFECTS OF INTERNALLY APPLIED ANIONS()

Using the whole-cell recording technique, we have examined the slow Ca 2+-activated afterhyperpolarization (AHP) and its underlying current ( I-AHP) in hippocampal CAI neurones of brain slices obtained from matur e rats. Specifically we have studied the effects of the anion componen t of various K+ salts commonly used to make the pipette filling soluti on that dialyses neurones during whole-cell recordings. Among the K+ s alts examined which included potassium methylsulfate, potassium methan esulfonate, potassium gluconate, potassium chloride, potassium citrate and potassium glutamate, stable AHPs/I-AHP and strong spike firing ad aptation could only be observed in neurones recorded with the patch pi pette solution containing potassium methylsulfate. These AHPs and firi ng patterns closely mimicked those recorded with sharp electrodes. Sim ilarly the sustained component of voltage-activated Ca2+ currents was more stable in neurones dialysed with cesium methanesulfonate than in those dialysed with cesium gluconate or cesium chloride. Although the mechanisms underlying the interaction(s) between internally applied an ions and ionic channels need further investigation, the present experi ments illustrate that in mammalian brain neurones at 33 degrees C, the Ca2+-activated I-AHP is dramatically altered by internal anions. We s uggest that among anions commonly used in electrode filling solutions for whole-cell recordings, methylsulfate is the least disruptive to in tracellular structures or Ca2+ homeostasis and permits stable whole-ce ll recording of the I-AHP and Ca2+ currents in mammalian CNS neurones.