Acetylcholine activation of K+ channels in cell-free membrane of atrial cells

Abstract

The activation mechanisms of K+ channels by muscarinic acetylcholine (m-ACh) receptors were examined in isolated atrial cells by use of patch-recording technique. In "cell-attached" patch recordings, ACh, present in the pipette, activated an inwardly rectifying K+ channel. In "inside-out" patches, activation of the K+ channel by ACh diminished with time following excision of the patch, but it resumed when GTP was present in the solution bathing the intracellular side of the membrane. The A protomer of pertussis toxin, together with NAD, inhibited the channel activation in the presence of GTP. Since pertussis toxin specifically ADP-ribosylates GTP-binding proteins Ni and No, which can interact with m-ACh receptors, and inhibits their functions, it was concluded that m-ACh receptors communicate with the K+ channel via GTP-binding proteins, probably Ni and/or No, in atrial cell membrane.

Cellular modelling: experiments and simulation to develop a physiological model of G-protein control of muscarinic K + channels in mammalian atrial cells

“…The K ACh currents evoked by various concentrations of ACh were recorded in the whole-cell configuration of the patch-clamp technique. Other experimental data, such as single channel current recording, were taken from published papers (Kurachi et al 1986;Ito et al 1991). …”

The role of members of the pertussis toxin-sensitive family of G proteins in coupling receptors to the activation of the G protein-gated inwardly rectifying potassium channel

“…Co-expression of Kir3.1 with Kir3.2, Kir3.3, or Kir3.4 results in currents that show many of the basic characteristics of the native channels in neurones and atria (6)(7)(8). Channel activation is abolished by pertussis toxin (PTx) treatment, implicating the G i/o family of G proteins (9)(10)(11). Although initially controversial, it is now well established that activation of these channels in native tissues and of the cloned counterparts in heterologous expression systems is via a membrane-delimited mechanism involving a direct interaction with the G ␤␥ dimer (12)(13)(14).…”

Membrane-delimited activation of muscarinic K current by an albumin-associated factor in guinea-pig atrial myocytes

“…One of the crucial findings that proved the membrane-delimited, G-protein-mediated control of IK(Ach) by the muscarinic receptor, was the sensitivity of the channel in inside-out, cell-free membrane patches to GTP applied to the internal face of the membrane [14]. In experiments using the inside-out configuration, massive channel activity was elicited upon changing from GTPfree to GTP-containing (5 J.1M) bathing solution.…”

“…These acute effects include activation of muscarinic K current [IK(Ach) ' [2]] and reduction of p-receptor stimulated Ltype Ca 2 + current (lc .. ) via inhibition of p-receptor-sensiCorrespondence to: L. Pott tive adenylyl cyclase [1]. Both actions can be identified at dilutions down to about 1: lOS (v/v), with half-maximal activity in the order of 1: 10 3 • In analogy to muscarlnic-receptor-mediated events [1,14,19,24] both actions of diluted sera are inhibited by pre-incubation of the myocytes with pertussis toxin, and thus are mediated by a defined class or type of G-protein.…”