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ACh‐induced rebound stimulation of L‐type Ca 2+ current in guinea‐pig ventricular myocytes, mediated by Gβγ‐dependent activation of adenylyl cyclase
Author(s) -
Belevych Andriy E.,
Sims Carl,
Harvey Robert D.
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.00677.x
Subject(s) - adenylyl cyclase , muscarinic acetylcholine receptor , medicine , pertussis toxin , endocrinology , forskolin , cholera toxin , stimulation , chemistry , agonist , g protein , receptor , biology
1 The effects that muscarinic receptor stimulation have on the cAMP‐dependent regulation of L‐type Ca 2+ currents were studied in isolated guinea‐pig ventricular myocytes using the whole‐cell configuration of the patch‐clamp technique. 2 The muscarinic agonist ACh inhibited the Ca 2+ current stimulated by the β‐adrenergic agonist isoprenaline (Iso), and washout of ACh revealed a stimulatory response that appeared as a transient rebound increase in the amplitude of the Ca 2+ current. The ACh‐induced stimulatory effect was not observed in the absence of Iso. 3 ACh‐induced rebound stimulation was also observed in the presence of H 2 histamine receptor activation and cholera toxin treatment, which like β‐adrenergic receptor activation enhance adenylyl cyclase (AC) activity in a stimulatory G protein (G s )‐dependent manner. ACh‐induced rebound stimulation was not observed in the presence of forskolin, which enhances AC activity in a G s ‐independent manner. 4 Pertussis toxin (PTX) treatment blocked both the stimulatory and inhibitory effects of ACh. Intracellular dialysis with QEHA, a peptide that binds free G protein βγ subunits, selectively antagonized the stimulatory effect, leaving an enhanced inhibitory effect. 5 Evidence for the expression of AC4, an isoform of AC that can be stimulated by Gβγ but only in the presence of Gα s , was obtained by Western blot analysis of guinea‐pig ventricular myocyte membrane preparations. 6 These results suggest that muscarinic receptor stimulation facilitates as well as inhibits cAMP‐dependent regulation of the Ca 2+ current and that the net response is a balance between these two actions. We suggest that the stimulatory effect is due to a direct activation of AC4 by the βγ subunits of a PTX‐sensitive G protein.