Caffeine response in pyramidal neurons freshly dissociated from rat hippocampus.
The effect of caffeine on the CA1 pyramidal neurons freshly dissociated from rat hippocampus was investigated with nystatin-perforated patch technique under voltage-clamp condition. Caffeine evoked a transient outward current (Icaffeine) in a concentration-dependent manner at a holding potential of -40 mV. The activation and inactivation of Icaffeine were accelerated with increasing caffeine concentration. The reversal potential for Icaffeine was close to K+ equilibrium potential. The Icaffeine was not blocked by apamin and 4-aminopyridine but suppressed by charybdotoxin, tetraethylammonium, quinine and Ba2+. Thus, the pharmacological characteristics of Icaffeine were similar to those of Ca(2+)-activated K+ current having a large conductance (IC), which generates a fast afterhyperpolarization (a.h.p.). Icaffeine was depressed by pretreatment with a membrane-permeant Ca2+ chelator (BAPTA-AM) and by depletion of the Ca(2+)-induced Ca2+ release (CICR) pool with ryanodine. A blocker of CICR sites, procaine, potently depressed the Icaffeine. In the absence of the extracellular Ca2+, an application of 10 mM caffeine depleted the caffeine-sensitive Ca2+ pools. Icaffeine recovered in an exponential fashion in the presence of the extracellular Ca2+. It was concluded that rat hippocampal pyramidal neurons have a caffeine-sensitive Ca2+ pool. Furthermore, the Ca2+ released from the pool evokes K+ current similar to IC current and hyperpolarizes the neurons.
Uneyama
H
H
Department of Neurophysiology, Tohoku University School of Medicine, Sendai, Japan.
Munakata
M
M
Akaike
N
N
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D001464:Barium / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D004594:Electrophysiology / Q000379:methods; D006624:Hippocampus / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009761:Nystatin / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D011343:Procaine / Q000494:pharmacology; D011712:Pyramidal Tracts / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012433:Ryanodine / Q000494:pharmacology; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D009761:Nystatin; D012433:Ryanodine; D001030:Apamin; D001464:Barium; D000001:Calcimycin; D002110:Caffeine; D011343:Procaine; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D002118:Calcium