Single K+ channels activated by D2 dopamine receptors in acutely dissociated neurons from rat corpus striatum.

Abstract

Corpus striatum neurons acutely dissociated from the brains of young adult rats had membrane surfaces suitable for Gi-seal recording. Whole-cell current-clamp and voltage-clamp recordings indicated that the cells remained electrically excitable after dissociation. Cell-attached recordings frequently revealed single-channel openings in the presence of dopamine or of the D2 dopamine agonist quinpirole. Channel openings were rarely or never observed in the absence of drugs or in the presence of quinpirole plus the dopamine antagonist haloperidol. The D2 antagonist spiperone was more potent at blocking the appearance of the channel than was the D1 antagonist SCH-23390. The channel reversal potential varied with the extracellular K+ concentration as predicted by the Nernst equation. The channel currentvoltage relationship was linear, with a conductance of m85 pS in the presence of 140 mM KCL. These results are consistent with the opening of single K+ channels following D2 dopamine receptor activation.The corpus striatum (caudate and putamen) is a major postsynaptic target of dopaminergic projections in mammalian brain (1, 2). Because of the role of dopamine in the actions of antipsychotic drugs (1, 2) and because of the potential usefulness of studying these actions with single-molecule resolution, we have studied the effects of dopamine at the singlechannel level.Patch-clamp recording in adult mammalian brain has been hampered by the need for dissociated cells. One way to obtain dissociated cells is to work with cultured embryonic tissue (3). However, rat striatal dopamine receptor radioligand binding sites are largely absent in the neonate and do not reach adult levels until =28 days after birth (4). A method has been described for enzymatically splitting the hippocampus along the pyramidal cell layer (5) but may not be useful for brain regions such as the striatum, which are not organized into cellular layers.Kay and Wong (6) have described a method for acutely dissociating adult guinea pig brain, based upon trypsin treatment in a slightly acidic Pipes buffer. Kay et al. (7) and Huguenard and Alger (8) have used this method to record from guinea pig hippocampal pyramidal neurons. We have made minor modifications in their procedure to dissociate striatal neurons of young adult rats. We report here that we have used these dissociated cells to obtain an initial description at the single-channel level of the actions of dopamine in mammalian brain. post partum, were the tissue source. The corpus striatum was rapidly and carefully dissected in a beeswax-coated Petri dish under ice-cold Pipes saline [120 mM NaCI, 5 mM KCl, 1 mM CaCl2, 1 mM MgCl2, 25 mM D-glucose, 20 mM Pipes-NaOH (pH 7.0 at 25°C, preequilibrated with 100% 02)1 and hand-minced with a scalpel blade into blocks of =2 mm per edge. The tissue blocks were transferred by using a wide-bore pipette to a 25-ml jacketed double-side-armr Wheaton Celstir stirring chamber, containing 130,000 benzoylarginine ethyl ester units of trypsin (Sigma type XI) in 12 m...

Modulation of secretion by dopamine involves decreases in calcium and nicotinic currents in bovine chromaffin cells.

“…A common dopamine-dependent action in different cell types has been described, where membrane hyperpolarization results from the activation of a K+ conductance (Ingram, Bicknell & Mason, 1986;Israel, Kirk & Vincent, 1987;Lacey, Mercuri & North, 1987;Sasaki & Sato, 1987;Freedman & Weight, 1988;Castelletti, Memo, Missale, Spano & Valerio, 1989;Gregerson, Einhorn, Smith & Oxford, 1989). This membrane hyperpolarization might then secondarily lead to diminished Ca2+ entry, and decreased secretion.…”

Molecular Mechanisms and Therapeutical Implications of Intramembrane Receptor/Receptor Interactions among Heptahelical Receptors with Examples from the Striatopallidal GABA Neurons

“…Also dependent on G i/o coupling, but independent of cAMP, D 2 receptors have been shown to modulate the activity of K ϩ channels. In many preparations, including acutely dissociated striatal neurons (Freedman and Weight, 1988), D 2 receptor stimulation has been shown to increase outward K ϩ currents, leading to cell hyperpolarization (Missale et al, 1998). Furthermore, other less well characterized cAMP-independent signaling pathways used by D 2 receptors, such as activation of PLC, inhibition of inward Ca 2ϩ currents, arachidonic acid release, inhibition of Na ϩ -K ϩ -ATPase and MAPK activation, have been reported (Missale et al, 1998;Yan et al, 1999).…”

Direct and Indirect Actions of Dopamine on the Membrane Potential in Medium Spiny Neurons of the Mouse Neostriatum

“…In the present study, however, the potential change by the activation of anomalous rectifier K ϩ currents during DA application could not be detected because the K ϩ equilibrium potential is close to the resting membrane potential. Similarly, it is possible that the positive shift of the reversal potential for the DA-induced slow depolarization is probably due to the contamination of the activation (Freedman and Weight 1988) or suppression (Uchimura and North 1990) of the inward rectifier K ϩ current via a D 2 -like receptor in the ventral striatal neurons because the equilibrium potential for the inward rectifying current is approximately Ϫ80 mV (Uchimura et al 1989a), which is a more positive value than the resting membrane potential.…”