Calcium antagonist effects on low-threshold (T-type) calcium current in rat isolated hippocampal CA1 pyramidal neurons.
In CA1 pyramidal cells freshly isolated from the rat hippocampus, the low-threshold (T-type) Ca++ current was induced by step depolarization to potentials more positive than about -60 mV from a holding potential of -100 mV, and reached a peak in the current-voltage relationship around -30 mV. The activation and inactivation processes of the current were highly potential-dependent, and the latter was fitted by a single exponential function. Organic and inorganic Ca++ antagonists dose dependently blocked T-type Ca++ channel in the order of flunarizine greater than nicardipine greater than D600 greater than diltiazem and La greater than Zn++ greater than Cd++ greater than Ni++ greater than Co++, respectively. The inhibitory effects of flunarizine, nicardipine and D600 were voltage- and use-dependent. It was concluded that rat hippocampal neurons possessed a definite class of T-type Ca++ channel characterized by the current kinetics and the high sensitivity to organic Ca++ antagonists. The pharmacologic nature differed from that in other tissues such as cardiac and smooth muscle cells, peripheral neurons and cultured cells.
Takahashi
K
K
Department of Neurophysiology, Tohoku University School of Medicine, Sendai, Japan.
Akaike
N
N
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects; D005110:Extracellular Space / Q000378:metabolism; D005444:Flunarizine / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D007424:Intracellular Fluid / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D011712:Pyramidal Tracts / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D051381:Rats
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D005444:Flunarizine; D002118:Calcium