Cannabinoid Receptors Differentially Modulate Potassium A and D Currents in Hippocampal Neurons in Culture

• Published in: The Journal of pharmacology and experimental therapeutics 1999-11, Vol.291 (2), p.893
• Main Authors: Mu, J, Zhuang, S Y, Kirby, M T, Hampson, R E, Deadwyler, S A
• Format: Article
• Language: English
• Subjects: 4-Aminopyridine - pharmacology; Analgesics - pharmacology; Animals; Benzoxazines; Cells, Cultured; Cyclic AMP - pharmacology; Dose-Response Relationship, Drug; Drug Interactions; Elapid Venoms - pharmacology; Fetus - physiology; Hippocampus - drug effects; Ligands; Membrane Potentials; Morpholines - pharmacology; Naphthalenes - pharmacology; Neurons - drug effects; Potassium - pharmacokinetics; Rats; Receptors, Cannabinoid; Receptors, Drug - antagonists & inhibitors; Receptors, Drug - physiology; Tetraethylammonium - pharmacology; Time Factors
• ISSN: 0022-3565; 1521-0103

Cannabinoid (CB 1 ) receptor activation produced differential effects on voltage-gated outward potassium currents in whole-cell recordings from cultured (7–15 days) rat hippocampal neurons. Voltage-dependent potassium currents A (I A ) and D (I D ) were isolated from a composite tetraethylammonium-insensitive current (I comp ) by blockade with either 4-aminopyridine (500 μM) or dendrotoxin (2 μM) and subtraction of the residual I A from I comp to reveal I D . The time constants of inactivation (τ) of I A and I D as determined in this manner were found to be quite different. The CB 1 agonist WIN 55,212-2 produced a 15- to 20-mV positive shift in voltage-dependent inactivation of I A and a simultaneous voltage-independent reduction in the amplitude of I D in the same neurons. The EC 50 value for the effect of WIN 55,212-2 on I D amplitude (13.9 nM) was slightly lower than the EC 50 value for its effect on I A voltage dependence (20.6 nM). Pretreatment with either the CB 1 antagonist SR141716A or pertussis toxin completely blocked the differential effects of WIN 55,212-2 on I A and I D , whereas cellular dialysis with guanosine-5′- O -(3-thio)triphosphate mimicked the action of cannabinoids but blocked the action of simultaneously administered cannabinoid receptor ligands. Finally, the differential effects of cannabinoids on I A and I D were both shown to be mediated via the well documented cannabinoid receptor inhibition of adenylyl cyclase and subsequent modulation of cAMP and protein kinase. These actions are considered in terms of cAMP-mediated phosphorylation of separate I A and I D channels and the contribution of each to composite voltage-gated potassium currents in these cells.