Protein kinase-dependent phosphorylation and cannabinoid receptor modulation of potassium A current (I-A) in cultured rat hippocampal neurons

Mu, J Zhuang, SY Hampson, RE Deadwyler, SA

J. Mu et al., Protein kinase-dependent phosphorylation and cannabinoid receptor modulation of potassium A current (I-A) in cultured rat hippocampal neurons, PFLUG ARCH, 439(5), 2000, pp. 541-546

45

INGLESE

Article

Physiology

PFLUGERS ARCHIV-EUROPEAN JOURNAL OF PHYSIOLOGY

0031-6768 → ACNP

439

5

2000

541 - 546

ISI

0031-6768(200003)439:5<541:PKPACR>2.0.ZU;2-9

The potent cannabinoid receptor agonist WIN 55,212-2 produces positive shif ts in steady-state inactivation of the potassium A current (I-A) in rat hip pocampal neurons via an adenosine 3',5'-cyclic monophosphate (cAMP)-, prote in kinase A (PKA)-dependent process. This effect is probably mediated by ph osphorylation or dephosphorylation of the I-A channel protein. The role of protein phosphorylation in this cascade was tested by testing cannabinoid a ctions in cultured hippocampal neurons (pyramidal cells) that were exposed also to either the catalytic subunit of PKA (PKAc), a PKA-specific phosphor ylation inhibitor (IP-20, Walsh peptide), or a potent protein phosphatase i nhibitor (okadaic acid). Cannabinoids such as WIN 55,212-2 produce a positi ve (rightwards) shift in the steady-state inactivation of I-A, thus providi ng increased current at a given membrane voltage. Cells dialyzed with PKAc showed a negative shift in I-A inactivation, opposite to that produced by c annabinoids, and similar to that produced by increased levels of cAMP. In a ddition, PKAc completely blocked the positive shift produced by WIN 55,212- 2. In contrast, dialysis of cells with IP-20 produced a positive shift in s teady state inactivation of I-A, similar to that produced by WIN, but the e ffects were not additive with cannabinoid receptor activation. The phosphat ase inhibitor, okadaic acid produced a small negative shift in I-A steady-s tate inactivation when administered alone, and blocked the positive shift p roduced by WIN 55,212-2. Okadaic acid also enhanced the negative shift in I -A inactivation when co-administered with forskolin. The effects of okadaic acid and WIN 55,212-2 were not additive, suggesting a common pathway. Thes e results demonstrate that I-A is altered by direct manipulations of the ph osphorylation status of the channel protein, and that cannabinoid effects o n I-A are probably mediated by dephosphorylation of the I-A channel.