Muscarinic and beta-adrenergic depression of the slow Ca2(+)-activated potassium conductance in hippocampal CA3 pyramidal cells is not mediated by a reduction of depolarization-induced cytosolic Ca2+ transients.
Combined intracellular and microfluorometric recording techniques were used to evaluate whether the inhibition by cholinergic or adrenergic transmitters of the Ca2(+)-activated potassium current (IAHP) in hippocampal CA3 pyramidal cells was mediated by an alteration of depolarization-induced change in cytosolic free Ca2+ concentration [(Ca2+]i). Low concentrations of isoproterenol (1-10 microM) and muscarine (0.25-1 microM) reversibly abolished IAHP without affecting concomitant Ca2+ transients or the steady-state [Ca2+]i. Only after application of higher concentrations of muscarine, [Ca2+]i increased; in the presence of potassium channel blockers, muscarine depressed Ca2+ currents and concomitant Ca2+ transients. These observations provide direct evidence that the inhibition of IAHP by isoproterenol and muscarine are not mediated by an alteration of Ca2+ dynamics.
Knöpfel
T
T
Brain Research Institute, University of Zürich, Switzerland.
Vranesic
I
I
Gähwiler
B H
BH
Brown
D A
DA
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D003600:Cytosol / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D006624:Hippocampus / Q000502:physiology*; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009116:Muscarine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D011188:Potassium / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D011976:Receptors, Muscarinic / Q000502:physiology*
D015221:Potassium Channels; D011943:Receptors, Adrenergic, beta; D011976:Receptors, Muscarinic; D009116:Muscarine; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine