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Accelerating effects of pentobarbitone on the inactivation process of the calcium current in Helix neurones
Author(s) -
Nishi K.,
Oyama Y.
Publication year - 1983
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1983.tb10001.x
Subject(s) - chemistry , egta , calcium , pipette , electrophysiology , biophysics , pentobarbital , phase (matter) , chromatography , anesthesia , medicine , biology , organic chemistry
1 The effect of pentobarbitone on Ca 2+ current (I Ca ), separated from other ionic currents was studied under voltage clamp using a suction pipette technique in Helix neurones. 2 Pentobarbitone depressed the maximal peak amplitude (MPA) of I Ca in a concentration‐dependent manner without shifting the current‐voltage (I‐V) relationships along the voltage axis. Increases in external Ca 2+ ‐concentration ([Ca 2+ ] ***o ) overcame the inhibitory action of the agent on MPA. 3 Pentobarbitone markedly accelerated the decay phase of I Ca which took a distinctly different time course from that of the control. The accelerating action of the agent on the decay phase of I Ca was not overcome by increases in [Ca 2+ ] o . In the presence of internal EGTA (20 m m ), pentobarbitone also accelerated the decay of I Ca . 4 Changes in pH of the external perfusing solution altered the potency of pentobarbitone in depressing MPA; in the presence of pentobarbitone (3 × 10 −4 m ) at pH of 7.0, 8.0 and 9.0, fractional inhibition was approx. 46%, 21% and 4%, respectively. 5 Internal application of pentobarbitone (10 −4 ‐10 −3 m ) inhibited MPA, but exerted no effect on the decay phase of I Ca . 6 Pentobarbitone (10 −4 m ) markedly accelerated the decrease of MPA of I Ca induced by repetitive stimuli applied at an interval of 150 ms, indicating a use‐dependent depression of MPA. 7 Results provide evidence that pentobarbitone has a dual action on I Ca , inhibiting MPA and accelerating the decay phase of I Ca .